Installing modern replacements is an option to be considered. But you give up a lot when you replace historic windows. Few modern windows are built with the workmanship that went into your old windows, and the cost of those few can be astronomical.

Can This Window Be Saved?
It may look ‘way beyond fixing, but this old window can be restored and made as energy efficient as any standard thermal replace­ment window.We replace a lot of windows. We probably replace nine old windows for every old window we restore and save. The fact is that most windows made in the past 60 years are not good windows. The post-war push to build a lot of new housing quickly virtually eliminated the traditional wood window. It took too much time to build and install the window, and a high level of craftsmanship that just was not available. Builders opted for steel and aluminum windows, and factory made, self-contained wood window units that did not need a lot of site preparation and wall modification. Just put them in the opening and nail them up. It was faster, it was cheaper, and builders then, as now, were for anything faster and cheaper. (For more on the post-war housing boom, see Postwar Styles: Cape Cod, Colonial and Ranch.)

Photo: Andersen Windows. Nearly all window manufacturers market windows designed to look like heritage windows. This Andersen window looks like an original Craftsman window. But most replacement windows last at best 40 years while original windows were built to last generations with proper care. This window starts at about $600.00 — not including installation. Restoring the original window is about half that and since the window is already installed, no installation is required.But the sad consequence is that most of the windows installed since the World War are not worth saving even if they could be saved, and most cannot be. Manufacturers that are not out of business don’t make those windows any longer, so parts just are not available. The only option, then, to fixing your window problems is to replace the windows.

But most pre-War housing, and some better housing built since the World War have shop-crafted wood windows. These most often can be saved, and as for parts — if you have a glass company, hardware store and lumber yard in your town, then you have all the parts you are likely to need.

OK, so old windows can be saved, but can they be made as energy efficient as modern windows? The answer is “yes”.

Most heritage windows can be restored and upgraded to rival the performance of a standard replacement window, and usually at a fraction of the cost. And there are other, nearly as important, advantages of repairing rather than replacing. You not only save on your own heating a cooling costs, which reduces waste and your carbon footprint on the planet, you also save the resources and energy cost required to manufacture new windows — which considering what new windows are made out of, is not an inconsiderable savings.

You also preserve, not just wonderful old-time workmanship, but the superb old growth wood from which your windows were made. We can’t build windows like that any more. It’s not that our craftsmen do not have the skill and experience. Any of our master carpenters or cabinetmakers could build a traditional window. But we can’t get that dense, heavy old growth wood, and the new wood is … well, we’re pretty sure it’s wood, but it’s not very good window wood.

Are Replacement Windows a Good Investment?

Jonathan Poore’s classic “Anatomy of a Double Hung Window” published in Old House Journal in 1932. This is how windows were made for hundreds of years. Every one of these parts is a single piece of wood that can be removed and replaced without replacing the whole window.Before 1996, primarily as a consequence of the pervasive and unceasing marketing of replacement windows after the energy “crisis” of the 1970′s (when gasoline prices jumped to an astounding $.80/gal. — oh, for the good ol’ days), it was nearly universally thought that replacement windows were vastly superior energy performers. But then the State of Vermont and the U.S. Army joined together to actually test the performance of restored heritage wood windows, not by using computer models and a laboratory setting, but with an actual field test.

They repaired and restored 150 windows all over Vermont, then tested them against replacement windows in similar homes. What they discovered was completely unexpected. They found that

No one was looking for a result like this. The researchers had assumed, like everyone else, that thermal replacement window would be more efficient. The question they were really looking to answer was how much more efficient. The last thing they expected to find was that new thermal replacement windows were not necessarily more efficient.

After this, other researches were prompted to start examining the issue. Their findings amply support the conclusions of the Vermont study, which is still on-going, by the way. It has been extended several times, and is now due to end in 2016. The important thing to note about all of these field studies is not a single one has found that replacement thermal windows were much better than restored old windows.

How Long to Pay Back Your Window Investment? Haberern’s Findings in Brief

For example, Keith Haberern, a professional engineer, in an study of New Jersey homes published in 2007 found that the annual energy savings of a modern double-pane replacement thermal window over an old wood window was insignificant. In fact, an old wood window with a good storm window outperformed a typical new thermal window, and was a lot cheaper with a short 4.5 year payback period. What Others Say
“… [i]f your windows are single-paned, look into the cost of adding storm windows for a fraction of the cost of new windows.”

Tom Silva
General Contractor
This Old House

“…While the thermal perfor­mance of a refurbished single-glazed window fitted with a tight storm can never quite equal that of the best factory-made double-glazed windows, the difference is not so great as to merit the replacement of old windows solely for reasons of improved energy efficiency…”

John Leeke
Save America’s Windows

“…Homeowners tell me they know something is wrong with rippng out all their old windows and throwing them away, but they don’t quite know what the alternative might be. They cannot find tradespeople to do the work…. If you are not a do-it-yourselfer don’t worry. More and more savvy tradespeople are recognizing this new marked for traditional window maintenance and repair services.

John Leeke
Save America’s WindowsOn th other hand, if you already had a wood window/storm combination, replacing it with a thermal window resulted in very little energy savings. So little, in fact, that the payback period was 240 years.

Taking a slightly different approach, researcher and energy consultant Michael Blasnik looked at the energy bills of houses in upstate New York both before and after replacement windows were installed and found the actual average annual savings per household was just $40.00 — not per window — but per house. Based on these findings, he calculated that it would take 250 years for the cost of the replacement windows to be repaid from energy cost savings alone.

Obviously there are reasons other than economic reasons to buy replacement windows. New window sashes tilt out for easy cleaning, they have several lock positions so the window can be opened slightly and still be secure. Old windows often don’t have these features (although most can be added). Or your old windows may have deteriorated to the point where they really can’t be fixed — although this is very unlikely. But if it is your intent to reduce your cost of heating and cooling to pay for your windows out of energy cost savings, think again. Unless you have actually found the fountain of youth, it won’t happen in your lifetime.

How Heat Loss Happens
How is it then that replacement window manufacturers can advertise huge energy savings from replacement thermal windows? Are the manufacturers just lying?

Not really (well, maybe just a little). They don’t do actual field studies, but rely entirely on computer models to predict how much energy will be saved. The problem is that their computer models are incomplete and, therefore, inaccurate. Heat is not actually lost the way the computer models say it is.

Reader Comments
Finally, an article on replacement windows that makes sense…. I’ve known for years that modern replacement windows were not a good fit for period homes, but I could never find information about repairing old windows that I could share with customers. How do I get reprints?

Carlos L., Denver, Colorado Restoration Remodeler

There is so much GREAT information in this article!!! I would not change a thing, …. it is the BEST article I’ve seen on making the case for window restoration and what I’ve been preaching to clients for years!

Jack A., Albany, New York ArchitectAs we discussed in our article on house insulation (Insulating Your Old House), heat moves in three ways, radiation, conduction and convection.

Radiation is how the sun’s heat gets to Earth in the form of electromagnetic waves. In hot, sunny climates like Arizona, radiation is a prime source of heat gain in the summer. In colder climates, like Nebraska, it is not nearly as important since while a lot of heat can radiate into your house, especially in direct sunlight, very little heat radiates out of your house in winter. But some does, and window manufacturer’s combat this form of heat loss through low-e (for “low-emissivity”) coatings that block heat while allowing light to pass through.

Conduction is more important in a net heating climate, like Nebraska. It is the movement of heat on a microscopic level from molecule to molecule within a material. Heat one end of a steel bar with a propane torch and soon the other end is too hot to touch. Heat moved through the metal through conduction until it reached the other end of the bar. To combat heat loss Infrared photograph of heat loss. Yellow and red show places where heat is escaping. Even after replacing old windows with new thermal windows, most heat loss from the house is through the windows. But a significant amount is also being lost through the wood framing. Wood is a better conductor of heat than the surrounding insulation.through conduction, window manufacturers use low-conductivity materials in window construction where possible. The problem is, the essential part of any window is glass, and glass is not a low conductive material. If it were, then the simple solution to window insulation would be to install thicker glass to slow down heat movement. But, unfortunately, glass conducts heat very well. One solution would be to create a vacuum between two panes of glass. We know that vacuum is an excellent insulator. The problem with this approach is that so far no one has been able to create a reliable glazing system that works in an extreme climate like ours in Nebraska. The temperature differences between the two panes of glass causes the rigid glass welds along the edge of the unit to fail through stress.

So the more usual solution is to fill the gap between two panes of glass with a transparent gas. The gas most commonly used is plain, ordinary, dry air. The problem with air, however, is that it supports convection currents, and convection also transfers heat.

Understanding Room Air Convection
Let’s say you decide to follow our advice and insulate your outside walls with blow-in fiberglass or cellulose insulation (see Insulating Your Old House). You call in your insulation contractor and tell him to insulate the entire wall except a 3′ wide by 4′ high space right in the middle. After he stops sputtering, he will explain, hopefully in a nice way, that for insulation to work properly every nook a cranny in your wall must be filled with insulation. Otherwise all your heat will escape through the uninsulated gaps.

Ok, this makes sense. It’s pretty clear that a 12 square foot gap in your insulation is not a good idea. But now lets replace the 3′ wide by 4′ high gap with a dual-pane thermal window. The result is the same — a 12 square foot gap in your insulation. In fact, it’s worse. Your uninsulated wall had an R-value of about R-3.22. (the siding, sheathing, interior plaster and other components of your wall have some insulating value, see The Insulation Value of Common Construction Materials). Your new window has an R-value of about R-2.2.

As far as heat is concerned, your window is just a weak point in your wall insulation, and like water, heat seeks the path of least resistance out of any container. Very little heat actually escapes through the walls or roof of a well-insulated house. Most heat gets out through the windows. This is due to a natural physical process by which windows tend to draw heated room air to themselves. This process is room air convection.

Room Air ConvectionThis diagram shows a vastly simplified room air convection process. Actual room air convection may involve hundreds, even thousands, of air currents, big and small, all tending to move heated room air toward the windows.

Convection is a natural physical process that occurs in any room that contains air. Heated air rises, cold air falls. As heated air comes in contact with the room’s windows, the air gives up some of its heat to the glass. Now cooler and, therefore, denser, it starts to fall. As it falls, still pressed against the glass, it gives up yet more heat, getting ever colder and denser, and falling even faster. This creates a vacuum which other warm room air rushes to fill. This new air is in turn cooled and also falls, continuing the cycle. Until someone figures out how to repeal the physical laws of thermodynamics, it is completely unstoppable.

Room air convection would not have much conse­quence if just the little bit of air directly in front of the window was the only air affected. But the vacuum formed by the falling cooled air draws heated air not just from above, but from both sides of the window, forming convection currents that very quickly reach to every corner of the room, directing almost all the room’s air to the window through one convection current or another.

Unfortunately the computer models used to predict heat loss do not take into account room air convection. In all fairness, convection is very complex and very hard to model. Climate scientists have been trying for decades to develop an adequate model of atmospheric convection. It takes a long time and a super-computer to produce even a rudimentary model.

To simplify measurement, window engineers simply ignore room air convection. Room heat loss models assume that heat tries equally hard to escape in all directions. So if only 10% of your room walls are windows, then the assumption is that only 10% of the room heat is trying to work its way through the windows. This assumption ensures that any computer model woefully underestimates the rate of heat loss through windows, which may be as hight as 90% in the real world.

So, the next obvious question is, since all the heat will eventually get out through the windows no matter what you do, why bother to insulate at all? The answer is that we want heat to escape as slowly as possible. We cannot keep heat from escaping. Eventually it will get out. The object of insulation is not to keep it from getting out, but to slow it down. The more it is alowed, the less often you have to add heat to make up for the heat loss.

Let’s fill a box with water. Now take a hammer and knock down one of the sides. All of the water will immediately spill out. Fill another box with water and drill a hole near the bottom of one side. All the water will run out, but it will take a lot longer. Insulation works much the same way. If you don’t insulate your walls, the room will empty of heat very quickly — not just through the windows, but through all parts of the wall. By restricting heat to escaping only through the windows, the process is considerably slowed. That’s why we insulate walls despite the big holes in the insulation occupied by your windows.

For much more information on how insulation works, see Insulating Your Old House.Convection is the movement of molecules within fluids (i.e. liquids, gases). Convection does not take place in solids because solids (with the exception of some unusual materials called rheids) do not flow, nor in vacuum, because there are no molecules in a vacuum to move around. But in gases such as air, convection is one of the major modes of heat transfer.

Air, if it is dry and still, is a surprisingly good insulator. But, unfortunately, air between two glass panes is almost never still. It flows inside the glass. The air touching the warm inside pane picks up some heat and starts to rise — warm air, as you know, rises. It soon reaches the top of the window sash where it cannot rise any further. Eventually it is pushed against the colder outside pane and gives up some heat. Now colder, it starts to fall and as it falls it continues to give up heat until it reaches the bottom of the cavity. There it is soon pushed up against the warm inside pane again, draws in some heat and start to rise once more. This cycle repeats continuously and has the effect of efficiently conveying heat from inside to outside where it is lost. If the heat difference between the inside of the house and the outside is large, the convection current moves faster, conveying more heat. If the difference is slight, it moves slower, but it never completely stops moving.

Measuring Heat Transfer in Windows
Thermal resistance in windows is measured in U-value. The lower the U-value, the better the window unit resists heat transfer. U-Value sounds a little arcane and mysterious until you realize that it is just the reciprocal of the more common R-value rating. To translate U-value into R-value, just divide 1 by the U-value. A good triple pane window with a U-value of .16 has an R-Value of 1/.16 or R 6.25 — not very impressive when you consider the minimum acceptable for walls in this part of the country is R-13. Even less impressive is the average thermal window which has an R-value of abut 2.2.

U-Value is determined by testing the window using a process established by the National Fenestration Rating Council. The NFRC does not do any testing itself, but establishes the testing process and certifies the laboratories in which the actual testing is done. According to the NFRC “[t]he rating system employs computer simulation and physical testing by NFRC-accredited laboratories to establish performance ratings for fenestration products and product lines.”

To test for U-value, the window provided by the manufacturer is placed between a hot plate and a cold plate inside a tightly sealed, environmental controlled chamber, and heat flow between the two plates is measured with a heat flux sensor. The unit’s U-value is calculated from how long it takes to heat to transfer from the hot to cold plates. The NFRC procedure has at least one advantage over older testing processes, and those still used in Europe — the entire window, including frame, is tested, not just the glass.

The problem with this testing procedure is that the rigidly controlled, virtually airless, environment is not a very realistic simulation of the real world environment windows actually inhabit. It tests only two of the three heat transfer methods: conduction and, to a much lesser extent, radiation. It ignores convection. But convection is how most heat loss occurs. The consequence is that the tests results are meaningless in the real world — unless, of course your world has no air.

If your windows are installed in a room that has no convection currents and in an environment that had no air movement outside the house, then the U-value results would be a reasonably accurate predictor of how the windows would perform installed in your walls. But there is no such place. All rooms have convection currents — a window itself creates convection currents in an insulated room — and there is no such thing as completely still outside air. If there was such a thing, then a window itself, again, would create its own outside air currents.

So, while U-value comparisons between window units may help you decide which of two windows is the better thermal performer in the abstract, it does not tell you much about how either window will perform in your house. For the most part this necessary research has not been done. Window manufacturers are not the least bit interested in showing that their windows do not perform as well as advertised, and no government agency seems to have been aroused enough to do a comprehensive formal field study — even though going green is now officially the government’s policy.

From the limited field studies that have been done, however, we know that actual thermal window performance is well below that predicted by U-value ratings. There is plenty of evidence that properly restored old wood windows with storms perform at least as well as new thermal windows, and in the long run, as seals start to leak and the fills and coatings that temporarily boost new window thermal performance start to degrade, restored old windows may perform better.So, in trying to combat heat loss through conduction by using double- and triple-pane insulated glass units, manufacturers have introduced the third major source of heat loss, convection. Now the problem is to control the effects of convection, and that’s very difficult to do. In fact, as of now, there are no really good solutions.

The one most often adopted is to replace the air between the glass panes with a heavier gas such as Argon or Krypton. Heavy gases are more viscous and flow more slowly, thus slowing down heat transfer. These gases can temporarily raise a window’s resistance to heat movement considerably. Unfortunately they are not permanent. They leak out over time, and every manufacturer that uses them admits that they leak. No one warranties in-fill gases against leakage. After 10 years they are all but gone and have been replaced by, you got it, plain ol’ air. So that extra $5,000 you spent for

a house full of Krypton-filled windows just went adios; and the environment got a nice dose of Krypton that it did not really need. We think temporary measures such as films that degrade and gases that leak should not be allowed in determining a window’s thermal resistance. And we suggest that if you are contemplating buying a gas-filled window, you pay attention only to the U-value rating without the gas — eventually you will be gasless — and there is no way to get a gas refill.

But convection does not occur just between panes of glass in a window. It also occurs in the great outdoors, and is a major source of changes in our weather. There is always some air movement outside. It may be just a mild breeze, or it may be a tornado. Even if you can’t feel it on those hot, muggy summery days, it’s still there.

Inside your house, the story is the same. Air is moving constantly, and, unfortunately, the air convection inside your house is an efficient heat conveyor that constantly moves warm inside air to the weak spots in the room’s insulation where it loses its heat to the great outdoors. The weak spots in the insulation of most rooms are its windows.

We already know that warm air rises and cool air falls. The warm room air next to a cooler window glass gives up heat to the glass and falls. This creates a slight vacuum which other warm room air rushes to fill. This new air is in turn cooled and falls. This would not have much effect if just the little bit of air directly in front of the window was the only air affected. But the vacuum formed by the falling cooled air draws heated air not just from above, but from both sides of the window forming convection currents that very quickly reach to every corner of the room directing almost all the room’s air to the window through one convection current or another.

This is the process by which almost all of the heated air in the room is lost, not through the well-insulated walls, but through the relatively poorly insulated windows. The windows, in effect, draw heat to themselves through convection currents and dispatch it to the outside. It is an unstoppable physical process as long as the house contains air.

Testing Window Efficiency
Unfortunately the standardized tests used by window manufacturers to rate windows do not take into account room air convection. In fact, room air convection is eliminated as much as possible from the normal, static tests because it is too hard to standardize and no one can agree on a dynamic test that includes room air convection (See Sidebar: Where to Find Window Parts
AA Window Parts & Hardware
800-804-0147
http://www.aawindow.com/index.htm

All About Doors & Windows
816-221-8543
http://www.allaboutdoors.com/

Blaine Window Hardware
800-678-1919
http://www.blainewindow.com/

Phelps Company
802-257-4314
http://www.phelpscompany.com/

Pickens Window Parts
513-931-4432
http://www.pickenswindowparts.com

Strybuc Industries
800-352-0800
http://www.strybuc.com/

Swisco
856-283-0390
http://swisco.com/“Measuring Heat Transfer in Windows”). So in the tests that assign R-values to windows (actually U-values which are just the reciprocal of R-values. See the sidebar R-value, U-value… What Do They Mean? for more information), convection is ignored. This makes the tests wildly inaccurate because it is room convection more than any other heat transfer method, that produces the most heat loss. So, while it sounds impressive that a new, double pane, window has an R-value twice that of an older, single pane window, this does not translate into ”The unfortunate consequence of static testing is that window manufacturers tend to build windows that score high on tests, but do not necessarily perform best in the real-world environment.”a window that is twice as energy efficient. It may be somewhat more efficient, but we don’t know precisely how much since there are, as of today, no accurate tests of real world window heat loss.

The unfortunate consequence of static testing is that window manufacturers tend to build windows that score high on tests, but do not necessarily perform best in the real-world environment. Most potential window customers know little about windows, but do know that a high R-value is better than a lower R-value, so to sell windows, window makers strive for as high an R-value rating as possible in independent static R-value tests.

So, while many replacement window manufacturers claim reductions in household energy use of up to 35% and even 40% after installing their replacement windows, most admit that these projections are based on static testing in laboratories and hypothetical computer models, not actual field testing. When these claims have been field tested, little or no actual savings have been found. Where an old wood window is restored and equipped with a good storm window, the old window system has been repeatedly to perform about as well as a double-pane thermal replacement window. And it costs much a lot less to restore an old wood window than it does to replace it with even an average, run-of-the-mill, thermal window.

Modern Window Design and Materials
In former times windows were engineered for longevity. Now, they are engineered for energy efficiency, with longevity being a lesser consideration. This focus has drastically changed how windows are designed and manufactured, and how long they last. Most modern windows have a expected lifespan of less than 30 years — some of the best may reach 40 years — but 10-30 years is more likely. The problem is not that the windows are poorly made. Today’s windows are usually very well made. The problem is the engineering and the materials used. They just don’t last like old wood windows. Complex Spring Balances
One type of modern tension spring sash balance. Compare to a simple iron weight hanging from a cord, and it is easy to see how many more pieces there are to malfunction in this mechanism.

Mechanical BalancesA comparison of old and new sash balances, for example, illustrates the difference. If you raise the sash of an old double hung window, it stays in place at whatever position you leave it. This is possible because the weight of the window is counter-balanced by two iron weights attached to the sash by ropes that ride in pockets built into the wall alongside the window. The mechanism is simple, and works by gravity. There is nothing to break but the ropes, which can be easily replaced and once replaced last between 50 and 100 years, or even 200 years if bronze chain is used in place of rope.

Some window manufacturers still make windows the old way. This Heritage Series double hung window with traditional weight and pulley balance from Kolbe and Kolbe Millwork Company, Inc. is available in a number of wood species, including oak, pine and cherry. If we did not make our own windows, this is the one we would buy.Modern, self-contained, replacement windows cannot use sash weight pockets built into the wall, so other balancing mechanisms had to be developed. These are all some form of metal spring. The tension in a spring is what holds the sash in place when the window is open. Spring ballasts, however, unlike simple iron weights, are complex mechanical devices prone to breaking. Metal springs themselves are subject to metal fatigue which can cause the spring to lose tension over time or even fail completely. We have replaced some worn out spring balances less than four years old.

Deteriorating VinylVinyl is another culprit. Vinyl deteriorates when exposed to ultra violet (UV) rays. Those of us of a certain age remember well how vinyl dash boards in the ol’ Ford used to crack and split after only a few years exposure to sunlight. The vinyl is better these days. UV inhibitors retard deterioration, but nothing can stop it entirely. Vinyl window parts, especially the thin, flexible vinyl used in balance mechanisms, will deteriorate over time, especially with repeated use. After a few years they become brittle, break and need to be replaced.

Vinyl softens at 165°, and its not that uncommon to see such temperatures in the unventilated space between window panes on a bright, sunny day. Excess heat can also cause vinyl to warp and twist. While vinyl window manufacturers say they have that problem under control, no manufacturer we know of actually warrants its vinyl windows against warping, twisting or cracking, so how under control can it be? For more information in vinyl window problems, see vinyl-windows.org for a roundup of government and other third party studies of vinyl windows.

Leaking SpacersDouble- and triple-pane glass in thermal windows are manufactured in what are called Insulated Glass Units (IGUs). Spacers between the glass panes not only separate the panes, but seal in the gas between the panes. Air between panes of glass must be very dry. If the spacer holding that two panes of glass together springs a leak, moist room air will get between the panes and condensation will form, which may lead to mold, mildew and other nasties inside your IGU where you cannot get at it. There is no cure for this problem. It cannot be repaired. The entire unit has to be replaced. Seals are much better now than they were when first IGUs were first marketed in the 1930s as Thermopane®. Still, no one has yet invented a seal that does not leak. Some leak sooner, some later, but they will all leak someday. The environment that spacers have to survive is brutal. Temperatures can be as hot as 180° in summer, plummeting to -30° in winter, or even worse. It’s very hard to come up with an adhesive that works for a long time in that kind of environment. It is common to find spacer leaks in even very good windows within 10 years of installation and in some poorly made windows within one or two years.

Window Sashes that Cannot Be RepairedLike today’s Integrated Glass Units, modern window sashes are often single units that cannot be taken apart for repair. They can only be replaced using a component provided by the original manufacturer. You have to hope the window manufacturer (1) is still in business and (2) still makes the part. And you can expect the replacement parts to cost nearly as much as a new window. The manufacturers have a monopoly on replacement parts for their own windows and are not at all bashful about charging all the market will bear.

Old Windows: Built to be Re-Built
What Others Say
National Trust for Historic Preservation

Is this link broken? Please report broken links.

“…Given that an average house has between 24 and 30 windows, and the typical replacement window unit costs between $500-1,000 each, does an investment of $12,0000 or more make sense? On the flip side, the cost to restore an existing window and add storm windows (where appropriate) will generally be much less….

Many window replacement manufacturers claim greater savings than actually occur. Since windows account for at most 25% of heat loss, the payback and time to recoup your investment in terms of energy savings could take between 40 and as much as 200 years, based on various studies. A study from Vermont show the saving gained from replacement windows as opposed to a restored wooden window with a storm is only $.60. The added problem is most replacement windows will not last as long as 40 years, much less over a hundred years. And some are being replaced only after 10 year of service.”

National Park Service

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“[We recommend] the retention and repair of original windows whenever possible. We believe that the repair and weatherization of existing wooden windows is more practical than most people realize, and that many windows are unfortunately replaced because of a lack of awareness of techniques for evaluation, repair, and weatherization.Wooden windows which are repaired and properly maintained will have greatly extended service lives while contributing to the historic character of the building. Thus, an important element of a building’s significance will have been preserved for the future.” (Emphasis supplied).Photo: Phelps Company,
Restored sash weight pulleys with new weight chains in place of pulley ropes. This is a 200 year repair.Unlike modern windows, old wood windows were made to last for many generations, so they were built to be repaired, over and over again, if necessary. The old-time craftsmen knew that their windows would last a good long time, but not forever. So they built windows that could be easily fixed when something finally did give way. An old wood window is put together so it can be un-put together — it can be taken apart and any of the individual parts repaired or replaced using common hardware components available at your local hardware store and ordinary wood available at your local lumber yard. There is no chance the parts won’t be available even 200 years from now, unless we simply run out of trees — which, despite the the strident alarms of the more radical wings of the environmental movement, is not all that likely.

There are no exotic materials in an old window, just wood, glass, iron, rope and a little bronze or brass for the hardware. No vinyl, no unpronounceable chemical compounds, just basic stuff available almost anywhere that has a lumber yard and a hardware store. Anyone with some basic carpentry tools, a little understanding of how windows work, and decent eye-hand coordination can restore an old window.

Restoring Window FunctionUnlike modern windows, old windows rarely break. They may stop working, but the culprit is seldom the window itself. It is accumulated layers of paint that have glued the sashes to the frame, and broken pulley ropes. These are easy fixes that usually take just a few minutes. The sash ropes we use today are not the ropes of 100 years ago. The cotton ropes used then had a life expectancy of just 25 years. The new nylon/cotton ropes last up to 100 years. Freed from decades of paint, with new pulley ropes, and with a little scraping and sanding, most old windows work like new. If you want the repair to last nearly forever, use bronze sash chain instead of rope. Some people don’t like chain because it’s noisy, but considering that a properly installed sash chain never has to be replaced again, the trade-off is, in our humble opinion, a no-brainer.

Repairing DeteriorationThe next step is to check for rot and deterioration. Water is a window’s worst enemy. Although poor design, sloppy installation, wood-loving insects and baseball-loving kids can contribute to a window’s demise, the usual culprit is wood rot caused by standing water.

We find this primarily on the sashes and stool or sill of the window. It’s not hard to fix. If the problem is minor, and exterior (which is where it usually is), then a little outdoor spackling and some new paint solve it. Photo: Gorell Windows & Doors.Adding a good storm window to a restored wood window increases its energy performance to the same or better than a standard replacement window.Otherwise there are special two-part epoxy fillers that are — or so their manufacturers’ say — even stronger that the wood being replaced. If the problem is even more serious we may splice in some wood or even remove and replace the deteriorated part with a new, matching, part made in our cabinet shop. If necessary, we can build and entirely new sash that duplicates the old one exactly. In 40 years we have had to do this exactly twice.

Photo: SpencerWorks Wood combination storm windows from SpencerWorks combine traditional appearance with up-to-date functionality and very efficient thermal performance.WeatherproofingNow we need to look at weatherproofing. Over the years the wood in your window has dried out and shrunk a little. This is the reason your sashes may be loose in their frames and sometimes rattle in the wind. Since the sash is now smaller, air can creep around the sash. The weatherstripping may also need attention. A lot of old window makers used bronze for weatherstripping, and it may be intact, but often it has come loose because the nails used in those days to attach the weatherstripping have worked themselves out — or the bronze may have been removed by some old painter too lazy to mask it off when painting. We use new spring bronze slipped around the sides of the sashes to eliminate air leaks, tighten them up in frame and provide a nice slick surface to ride on. Horsehair felt made specifically for windows, or silicon bulb weatherstripping (but not rubber or plastic which do not last) can be used where the sashes meet the frame at top and bottom and at the meeting rail to bar air infiltration.

Spring bronze in the sash channel not only seals air leaks but provides a slick surface for the sash to slide up and down on.Insulating Around WindowsOnce the weatherstripping is done, we look at the insulation where the window meets the wall and in the sash weight pockets. Even if you have had your old house insulated, the insulators usually miss that small 1/2 inch or smaller gap between the window frame and the wall stud. We seal this area with low-expansion foam.

The pocket on each side of the window that holds the sash weights is also likely to be empty of any kind of insulation. Obviously we can’t fill it with foam because the sash weights need to move freely so the window will work properly. But the sash weights do not take up all of the space in the pocket, and the space they don’t take up can be insulated using a high R-value rigid board like polyisocyanurate (we don’t try to pronounce it either — its “poly-EYE-so” to us) which has a rating of R-7.2 per inch. We use 2-1/2 to 3″ of it in total together with expanding foam to arrive at a total R-value of R-18 to R-22 in the sash pocket — which is probably more than the R-13 to R-19 you have in your walls.

Replacing Single-Pane GlassWhat we never do, and don’t recommend, is replace single pane glass with dual pane glass. We used to try this, but it never worked very well. Old sashes are just not milled for the extra thickness of dual pane glass, and the sash pulley/weigh system is not designed for the increased poundage of dual pane glass. And, in the end, the gain in energy performance, if any, is negligible. A much better choice is to install a good storm window over restored sashes. Unless its cracked or broken, leave the glass alone.

How to Restore an Old Wood Window
Learn the basics of restoring old wood windows from this video by Preservation North Carolina. It won’t make you a window preservation expert, but it will get you started safely. If you have never restored a window before, you might check out our article Can I Do It Myself before you begin.

Adding Storm WindowsIf this seems like a lot of work, it is. But restoring your old window is about half the price of replacing it with a new thermal window, and wastes nothing. Old growth hardwood is saved from the landfill, and a lot of good old-time craftsmanship is preserved. A typical window can be restored for between $200 and $300. Of course it is not yet as energy efficient as a new window. For that we are going to have to add a storm window. ”High-quality equivalent replacement [window] units have been shown in practice to cost as much as three times that of restoration.”

A good quality white aluminum storm window installed will run about $80. An upscale wood combination storm window from a company like SpencerWorks will cost a bit more. If you already have storm widows, then you are just that much ahead. But assuming you don’t, your cost to repair your old wood windows and add a good storm window is about $325.00 vs. $500 and more to replace them. This is a savings of $5,500.00 in a 20-window house. For your investment you get a window that should be good for another 100 years, while a replacement window is doing very well to last 30 years. Your window performance is just as good if not slightly better and you saved 45% of the cost of installing replacement windows.

If you really want to save energy costs, assuming your attic and walls are already insulated at least to code, your heating and cooling system is already very high efficiency and all your doors are weather-stripped, go buy a high efficiency water heater ($1,000), put $4,400 in the bank against a rainy day, and treat yourself to a really lavish steak and lobster dinner ($100.00), for being “energy smart”. Just the water heater alone will save many times more energy dollars than a whole houseful of replacement windows.

Do New Windows Save Energy?
Electricity from Coal
The average thermal energy content of a ton of coal is 6,150 kilowatt hours (usually written as 6,150 kWh/ton). But not all of that energy is turned into electricity in the power plant. Most goes out as heat. Only 40% on average becomes electricity in a very efficient coal-fired plant — or about 2,460 kWh/ton.

A 500 megawatt coal fired power plant produces 3.5 billion kWh per year, burning 1.43 million tons of coal to do so. It also produces a lot of pollution, including…

• 10,000 tons of sulfur dioxide, the main cause of acid rain,
• 10,200 tons of nitrogen oxides which is one of the principal ingredients in smog, and also contributes to acid rain,
• 3,7 million tons of carbon dioxide, the primary greenhouse gas associated with global warming.

And it produces small amounts of just about every other element in the periodic table, including radioactive elements. In fact, a typical coal-fired generating plant emits more radiation into the atmosphere than a nuclear power plant.”Replacement windows cannot possibly save enough energy during their lifespan to pay back even the energy invested in their manufacture.”One of the fastest ways to get tossed out of our decidedly un-pretty, over-the-warehouse offices is to start talking about how environmentally friendly your company’s replacement windows are. (Its not the fastest way. The fastest way is if Abby, our old warehouse dog, decides she doesn’t like you. She is a remarkable judge of character.)

Replacing a window means that the old window is discarded, usually in the landfill. What is thrown away with an old window? A lot of irreplaceable old growth lumber, hours of careful craftsmanship, and a little American history. It took work and energy to build the window in the first place — to fell the tree, mill the lumber, build the window and install it. That is all now in the trash.

And it takes a lot more energy to build the replacement window. Energy expert Keith Haberern estimates that building a new replacement window requires 4.3 million BTUs. of energy. If this sounds like a lot, keep in mind that it’s not just window manufacturing that uses energy. It’s producing all the components and materials that are go into the manufacturing process. Making the glass, felling the trees and sawing the lumber, producing the paint, plastics, metal fasteners, even the paper labels all involve energy expenditure. Not to mention all the shipping involved — some of it from half-way around the world. By the time the window leaves the factory the total energy investment in the window is very substantial.

How much energy is 4.3 million BTUs? It takes about 13,000 kilowatt hours of electricity to produce 4.3 million BTUs. And it takes 13.65 tons of coal to generate that much electricity (according to Department of Energy estimates). In an entire year, an average home in Nebraska uses 18,000 kilowatt hours. So one replacement window embodies almost 9 months of household power usage. That’s for just the one window. If you have the average 20 windows in your house, just building your windows will use nearly 15 years worth of household energy. So even if your replacement windows saved 25% of your electric bill (and there are no replacement windows that come even close to that), it would take 60 years to pay back just the energy used to build your new windows. The math just does not work out. The life expectancy of the windows is less than the payback period.

Which is why, if you are a window salesperson and start talking about your green replacement windows, you are going to get the bum’s rush. We hate to be impolite, but there are absolute limits to civility.

Source: www.StarCraftCustomBuilders.com

1. Testing the Energy Performance of Wood Windows in Cold Climates. James, Brad and Andrew Shapiro, Steve Flanders and Dr. David Hemenway. 1996 p. i- iv, 1-3. 64-70 (part of 102-page document)

• Study measured energy efficiency and cost of range of renovation and replacement options.
• Replacing a historic window does not necessarily result in greater energy savings than upgrading the window.
• The decision to replace or renovate a window generally should be made on the basis of considerations other than energy cost savings.
• These include life-cycle costs, historical and architectural significance of window, comfort, maintenance and operability. However, energy savings should not be ignored.
• Air leakage at the rough opening can contribute greatly to window heat loss. Sealing this leakage can significantly reduce heat loss and be cost-effective.
• Exterior storm windows can reduce air leakage by 45%-75%.
• Interior storm windows can reduce air leakage by 80%-95%.
• Weather-stripping also can significantly reduce air leakage.
• Storm windows or double-glazing can significantly reduce thermal heat loss.
• Quality of installation or renovation affects performance of all options.
• Energy loss attributable to windows is about 20% of whole house loss.

2. Creating Windows of Energy-Saving Opportunity . Shapiro, Andrew and Brad James. Home Energy Magazine. Sept.-Oct. 1997

• Window heat loss due to thermal conduction/convection/radiation is much greater than heat loss due to air leakage. Air leakage accounts for a relatively small part of the total heat loss cost of a window.
• The air leakage rates of old windows vary widely depending on their condition.
• In comparing various types of renovations and replacements, the largest energy cost savings was projected for replacing a loose single-pane window with a double-glazed low-e window ($20/year/window). Replacing a tight, weather-stripped single-pane window with a double-glazed low-e window reduced energy cost about $5.30/year/window.
• The second largest energy cost savings came from installing a storm window over a loose window ($16-$19/window).
• Weather-stripping a loose window saved $14-$15 per window per year.
• Installing an interior low-e storm window over an average single-pane window offers energy cost savings similar to replacing the window with a double-glazed low-e window ($6.20 vs. $6.80/year), but at a much lower cost.
• Replacing just the sash of a window offers little energy cost savings over retaining and renovating the sash ($14-$15/year vs. $15/year).

3. Windows and Window Treatments. Sept. 2004. Kinney, Larry. Prepared by Southwest Energy Efficiency Project for U.S. Department of Energy’s Building America Program.

• Provides overview of current window technology
• Low-e coating on the outside surface of the inner pane of a double-paned window reflects interior radiant heat back into house.
• Windows that allow more solar heat gain can be used on the south-facing facades to provide passive solar performance in the winter, although this increases cooling load in summer. Overhangs and shades can counter-act the latter.
• In cold weather better insulated windows not only lower heating needs, but also reduce or eliminate moisture condensation, increase comfort, and may allow for a downsized heating system.
• Study shows energy loss or gain for single and double-pane windows at different orientations in winter and summer at Denver’s latitude. Overall, double-pane windows lose 10 times less heat in winter than single-pane (btu/sq ft/day), and have 40% less summer cooling load.
• Study shows results of computer simulation (“RESFEN” program) of energy costs and peak demand associated with 6 different new window types in Southwest cities, including Denver. Effects of prototype automated exterior shutter system, interior shades and overhangs were included in simulation. Single-pane windows were not included.
  • Clear-glass, insulated, double-pane, aluminum-frame windows were calculated to account for 46% of total heating and cooling costs for a 2,000-square-foot, single-story house in Denver ($307/year for all windows). Low-e coated, insulated, triple-pane windows and double-pane windows with automated exterior shutters yielded the lowest energy cost: 13% and -8% of total house heating and cooling costs, respectively.
• Calculates payback time for upgrading when purchasing new windows from less expensive, lower quality windows to more expensive, better quality windows (but not for purchase itself).

4. Window Selection Tool for Denver , energy use and costs for different types of windows, Efficient Windows Collaborative website

• Heating and cooling costs for typical Denver house with clear single-pane windows estimated at $1464/year; for house with low-e coated, argon/krypton gas-filled, double-glazed windows, $1254/year, about $200/year difference.
  Articles on windows and energy efficiency

5. Windows: Understanding Energy-Efficient Performance. Fisette, Paul. 2003. Online at University of Massachusetts , Building Materials and Wood Technology website. With graphics from his “Understanding Energy-Efficiency Windows” on Fine Homebuilding magazine website (based on his article in Fine Homebuilding magazine, Feb.-March 1998).

• Overview of how windows lose and gain energy and how window energy efficiency is measured
  • 30% of house’s heating and cooling energy may be lost through windows
  • 50% of house’s heating and cooling energy maybe lost due to air leakage
  • Energy savings, heating/cooling system size, maintenance costs, replacement costs should be factored into selecting windows.
• Overview of energy-efficiency features currently available in new windows
• Graph of heating and cooling costs for St. Louis , MO (4,948 heating degree days vs. Boulder – 5,554 heating degree days) for different windows:
  • house with single-pane windows: 80 million btu’s/$525 per year; house with low-e, argon-filled, double-pane windows: 50 million btu’s/$350 per year (about $200/year difference)

6. What Should I Do About My Windows? Mattinson, Bill, Ross DePaola, and Dariush Arasteh. Home Energy magazine. July-August 2002.

• Reviews decisions-making process for window retrofits, considering energy savings, comfort from drafts, aesthetics, convenience, condensation, installation cost
• Provides energy performance values for different types of window, including single-pane (u-value, solar heat gain, draftiness indicator)
• Describes RESFEN, software that calculates home energy costs for various window types
• Describes range of retrofit options, from re-conditioning to replacing windows
• Shows sample annual window energy costs for different window types and different levels of air leakage (Table 2), including: $437 for loose, leaky single-pane; $356 for tight single-pane; $138 for tight single-pane with low-e exterior storm; $100 for low-e double-pane with exterior storm

7. Replacing Windows. Energy Star, Remodeling Guide. Online.

• Replacing windows is rarely cost-effective based solely on energy-savings.

Storm window articles

8. Storm Windows Save Energy. Turrell, Colleen. Home Energy magazine. July 2000

• Overview of results of 1998 study of two windows with and without storm windows
• Storm windows make a substantial difference in reducing heat loss and air leakage: Total energy loss was reduced by 55-68% at low wind speed to 62%-80% at higher wind speed.
• Storm windows make the biggest difference on the lowest quality windows and at higher wind speeds.
• Weatherization is somewhat less successful at reducing air leakage than adding storm window.
• Storm windows take extra effort and time.

9. Storm Windows. US. Dept. of Energy, A Consumer’s Guide to Energy Efficiency and Renewable Energy. Online.

• Storm windows add little insulation to single-pane windows, but do reduce air leakage.
• Overview of types of storm windows

Historic window restoration articles

10. Preserve Those Old Windows. Leeke, John. Traditional Building magazine, date n/a

• Construction and remodeling industry is oriented toward selling new products. It takes less labor and technical knowledge to replace a window than restore it. There are few tradespeople who are experienced in maintaining and repairing old windows.
• Question of replacing versus restoring old windows should be addressed on a case by case basis.
• If replacing windows, custom reproductions are available.

11. Wood Window: Still Vital. Boorstein, James. Traditional Building magazine, date n/a

• Longevity of new window materials is unknown, whereas historic windows have been in service for over 75 years and can be restored to last another 50 or more years.
• Energy, resource use, pollution and waste associated with producing new windows and disposing of discarded ones should be considered in energy efficiency of new windows: energy used to manufacture and transport raw materials; energy cost and environmental impact of replacing less durable materials more often; adding more waste to landfills, of which largest component is construction debris.
• Labor to maintain and restore old windows also contributes to local economy.
• Architects need more education on evaluating options for older windows; information is less readily available than information on replacing windows.
• Many historic windows are discarded simply due to a broken sash cord.

12. To Replace or Not to Replace. The Office of Allen Charles Hill. Observations 23. Online.

• Asserts that double-glazed divided-light sashes do not look historic because muntins must be wider to hold greater glass weight and hide spacers and sealers.
• Seals in double-glazed windows start failing in 30 to 40 years or less.
• Repair of double-glazed windows is expensive.
• Windows are only one part of building’s thermal envelope; for example, wall insulation and old heating system could be improved as well or instead.

13. The Repair of Historic Wooden Windows. Myers, John. Preservation Brief 9. 1981. National Park Service Preservation Assistance Division.

• Methodology for evaluating and repairing historic windows
• How to first evaluate architectural and historical significance of windows and then evaluate physical condition of each window
• Describes levels of and techniques for repair, ranging from routine maintenance (simplest, least expensive) through structural stabilization to parts replacement (most difficult and expensive)
• Overview of weatherization, and replacement considerations when repair not possible
• Energy efficiency should be one of several factors considered, especially because renovated window with storm window can have .44-.49 U-value

14. Restoring Window Sashes. Gibney, David. Fine Homebuilding magazine. Feb.-March 2004.

• Outlines restoration techniques for old windows, as well as storm window options.
• Repairing old windows and adding storm windows offers a better return on investment than replacing them.
• Old windows are usually made of high-quality wood that is stronger, more durable and more reparable than new materials.
• Original glass is an important feature to preserve.

Energy and old homes

15. How to Save Energy When You Fix Up the Outside of Your Not-So-New House. Retrofit Best Practices Guide. January 2004. Oak Ridge National Laboratory website

• Storm windows cost much less than replacement windows but can potentially save nearly as much energy, especially those with low-e coating.
• Replacing single-paned wood frame window with double-paned vinyl window reduces window heat loss by 48%; installing low-e interior storm window instead reduces heat loss by 46%; installing low-e exterior storm window, 35%.
• Sealing air gaps between walls and windows saves 3-7% of whole house energy.
• Insulating uninsulated wall cavity saves 18-24% in heating and cooling costs; adding exterior insulation (beneath siding) saves 4-12% in energy costs.

16. Home Energy Checklist. American Council for Energy-Efficient Economy, Consumer Guide to Home Energy Savings. Online.

• Worst air leak culprits are usually not windows and doors, but utility cut-throughs for pipes, gaps around chimneys and recessed lights in insulated ceilings, and unfinished spaces behind cupboards and closets.

Online energy and climate change data

17. Household air leakage pie chart, U.S. Dept. of Energy, Energy Savers page

• Air leakage from house:
  • 31% at floors, walls, ceilings;
  • 15% at ducts;14% at fireplaces;
  • 13% plumbing penetrations;
  • 11% at doors;
  • 10% is at windows.
• Household energy usage pie chart, Boulder Office of Environmental Affairs, Residential Energy page
  • Space heating comprises 57% of household energy use.
• Household energy usage pie chart, U.S. Dept. of Energy, Energy Savers page
  • Space heating comprises 49% of household energy use.
  • Windows account for 10-25% of heating bill.
  • Storm windows can reduce heat loss through windows by 25-50%.
• Personal Greenhouse Gas Calculator, EPA Global Warming Resource Center page (tools>calculators)
  • Average household could reduce greenhouse gas emissions by 5% or 3,320 lbs. per year by replacing single-pane windows with Energy Saver windows.
• Greenhouse Gas Savings Actions savings table , Boulder Office of Environmental Affairs, Personal Actions Checklist
  • Average household greenhouse gas savings by improving building shell:
    • 4% by adding attic insulation;
    • 3.5% by sealing large air leaks;
    • 2.3% by upgrading to high-efficiency low-e windows;
    • 1.8% adding basement insulation;
    • 1.1% by adding wall insulation;
    • 1% by reducing leaks from windows and doors (EAO website, ghg action checklist)
  • Upgrading to energy-efficient windows ranks “medium” on a scale of “no cost” to “high cost” relative to amount of gas reduced.
• No printout available:

RESFEN, software for calculating heating and cooling energy use and costs of windows in residential buildings (downloadable for free at Lawrence Berkeley National Laboratory website (www.windows.lbl.gov )

• Program calculates energy use and costs for whole house and for windows only, based on house and window information input by user (construction type, geographic location, window type, electricity and gas costs).
• Annual heating cost for 2000 s.f., two-story, wood frame house with crawlspace, gas heat and moderatelysealed single-pane windows in Denver at January 2006 rates: $1340; heating energy use: 129.8 MBtu
• If windows for above house are double-glazed, low-e, annual heat: $1021; heating energy use: 99MBtu

Source: www.BoulderColorado.gov

Our study of old windows showed that the energy savings are similar for a variety of retrofit and replacement strategies. Rates of return on investment for energy improvements are quite low when starting with typical or tight windows with storms in place, but are significantly higher when renovating loose windows with no storm.

The difference in annual energy savings between renovating an old sash and replacing it with a new one was very small–retrofits saved only a few dollars.

Source: www.ci.albany.or.us

Read Full Study Here [PDF]

To put that in perspective – the amount of energy lost through doors and windows in the U.S. every year is roughly equivalent to all the energy we get from the oil carried by the Alaska pipeline!

Any opening in a building’s envelope – in its outer shell – is technically called fenestration, a term that includes windows, skylights and doors. Obviously, fenestration is important if you’re concerned about energy efficiency.

Since windows outnumber doors in most buildings, they deserve the most attention. You can either fix them to make them as efficient as possible, or you can replace them with some of the new technology that has been introduced in the last several decades.

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Today’s Windows – How They Work

Early windows were little more than holes cut in walls to let light and air into rooms. With the addition of glass in movable frames, a major improvement in building comfort was achieved, allowing closed windows to let in light and block the winter chill.

Over the past 20 years, windows have become increasingly more sophisticated, using new materials with more energy-efficient properties. Single-pane glass has been replaced by double, triple and even quadruple panes, with insulating materials separating the layers. Inert gasses have been pumped between the panes, adding to the window’s insulating properties. Even the glass itself has been coated to reflect heat.

These innovations mean that windows can significantly contribute to a home’s comfort and energy efficiency. By letting in sunlight, they provide warmth in winter, which will save energy and lower monthly heating bills. Proper design and the use of exterior shading can also lower cooling costs in the summer.

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How Energy Flows

To appreciate the improvement in today’s windows, it is helpful to understand three ways that energy can flow through them.

• Air can carry heat in or out of a window. Intentional air flow is called ventilation. Unintentional air flow – leakage – is called infiltration.
• Heat – or cold – can flow through the frame and the glass.
• Solar radiation – sunlight – can pass through the glass and can heat whatever is inside the building.

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Ventilation and Infiltration

Well-placed windows allow for natural ventilation, which can significantly reduce cooling costs in the summer. But infiltration – unplanned air leakage through a window’s joints, cracks, frames and sashes – can account for as much as 15 percent of a home’s heating and cooling losses. It can make a home much less comfortable and more costly to operate.

Different types of windows can allow more infiltration. For example, a horizontal sliding window may not be as airtight as a window with a swinging sash. In addition, the overall quality of the window can affect infiltration – some windows are built better than others.

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Modern Windows – Think of Them as Thermos® Bottles

When there is a difference between inside and outside temperatures, heat transfers through a window. It’s lost to the outside during the heating season and is gained from the outside during the cooling season.

A window’s thermal performance – which can be measured at the center of glass, the edge of glass and the frame – is rated with a U-factor, its overall ability to resist heat flow.

Have you ever tried to drink hot coffee from a drinking glass? If so, you know that glass is a very good heat conductor. The outside of the container can quickly become too hot to hold. Using two layers of glass with an air space between – the idea behind the Thermos bottle, incidentally – dramatically cuts the heat flow.

Single-pane windows can act like that drinking glass, conducting heat to the outside. Dual-pane windows, with a 1/2 inch to 3/4 inch air space between sheets of glass, work like a Thermos bottle to cut down the flow of heat. If you replace the air between the panes with an inert gas like carbon dioxide, argon or krypton, the window will transfer even less heat and be even more efficient.

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The Frames

Before dual-pane windows, the material used for window frames was not of great concern, since a single pane of glass conducts heat about the same as a solid aluminum frame. With more efficient glazing, however, new materials and new designs were used to make window frames themselves less conductive. Today, wood, fiberglass, vinyl or vinyl-clad wood window frames will generally perform better and provide more comfort than metal frame windows that do not have a thermal break – a piece of non-conductive material sandwiched between the metal parts to cut down the flow of heat.

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The Glass

Even in dual-pane windows with less conductive frames, the type of glass and type of spacers used to create the air space can improve energy performance. Low emissivity (low-E) coatings can help to decrease the U-factor; the lower the U-factor, the more efficient the window becomes. A low-E coating is a microscopically thin layer of metal or metal oxide deposited on window glass. The coating reflects warmth back into the home in the winter and prevents unwanted heat from entering the home in the summer.

When shopping for windows, look for the overall U-factor rating. The lower the U-factor, the better the window’s energy performance will be.

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Windows that Help Block the Sun

Sunlight passing through a window adds heat to a room – desirable in winter, but generally unwanted in the summer. Solar heat gain through windows may account for 30 percent or more of a home’s summer cooling requirements.

The amount of heat from direct sunlight through a window is measured as Solar Heat Gain Coefficient (SHGC). The lower the coefficient, the less solar heat comes through the window.

Window tints such as bronze and green keep out more of the sun’s heat than clear glass does. Low-E coatings used to lower window U-factors may also reduce a window’s Solar Heat Gain Coefficient. Keep in mind, however, that by tinting your windows to keep out heat, you may make it harder to see through them.

Consider a window’s orientation to the sun before selecting window tints. South facing windows gain the most beneficial heat in winter, so their Solar Heat Gain Coefficients could be higher and therefore allow more heat gain. If these windows are properly shaded – say, by deciduous trees – they will allow little heat gain in summer. Note: careful consideration should be made to what climate zone in California you are in and orientation of the window before selecting fenestration.

Solar Heat Gain Coefficients for north windows can also be higher, since they get little direct sun and do not contribute much heat any time of the year. East and west facing windows should have low SHGCs, since they get direct morning , mid-day and late afternoon sun and are responsible for most of the solar heat gain during summer.

Often the best strategy to reduce heat gain in the summer is to provide exterior shading through overhangs, awnings, shade screens and trees.

Source: www.ConsumerEnergyCenter.org

The general differentiation of windows beyond style (double-hung, casement, sliding, etc.) is the glass or glazing and the framing material. There are three main types of frame materials, each addressing several lifespan aspects of the windows.

Wood
A natural product, it is said that the industry grows thousands of windows a year. A moderate insulator (R1 per inch), it requires some maintenance (stain or paint) to prevent rot from moisture build-up. It is warm to the touch in the coldest winters and room temperature in the summer.

• Wood Window Association

Vinyl
A product of the plastics industry, it uses a nonrenewable petroleum source for extrusion. The final product is usually non-paintable, but does offer a lifetime free maintenance. Some radical climatic changes over time may stress the material to failure at the joints allowing water penetration, though it is rare with quality manufacturers.

Aluminum
A metal commonly used in cookware for its thermal conductivity and in airplanes for its strength to weight properties, it features lifetime free maintenance, but usually cannot be painted. Over the course of many years aluminum will oxidize leaving a dull pitted appearance. If not well insulated with a thermal break, it is very cold to the touch in winter and hot in summer.

Beyond the framing material one has a wide selection of glazing or glass combinations to fill the sash or window panels. Once the standard, single pane glass is usually available only as an option, whereas double pain insulated glass is the norm. But this will not last long with the triple pane windows on the market combined with high energy bills.

With Rising Utility Bills, triple glaze glass has become available. What material or substance placed between the panels differentiates dual glazed window systems. With the injection of a noble gas like argon, xenon, or krypton between the panels, the conductive resistance of the window improves. Suspending a polyester film covered with a highly reflective material like silver further improves window performance. Sometimes the second glass panel (interior facing) is spayed with a special coating, called low-e*, which acts as a reflective interface.

When ordering windows it is best to get the low-e coated windows or the suspended film type for greater seasonal comfort and energy savings.

Source: www.GreenConcepts.com

Triple paned (also known as triple glazed) windows are of course heavier and more expensive than double paned windows, as you might expect. But a window with three panes is an investment rather than a purchase.

This is the choice for the homeowner who wants to make excellent long term savings to energy costs. And so can accept that the initial price of the window will not be made up in heating bill reductions for quite a few years.

The Lowest Of U-factors

Remember that three panes of glass, means six surfaces of windowpane. This in turn means more surfaces for low-e coatings that can keep the thermal energy produced indoors where it belongs – and not heating up the air outside your home!

There are also insulation benefits to triple glass windows because of the two internal fill spaces rather than just one as in double paned. These spaces are filled with air, argon or sometimes krypton and work to stop heat transfer, as well as cutting down on noise.

A window is only as effective as its frame allows it to be however. So be sure to check yours is being made by a quality manufacturer who provides full information about U values and other NFRC (National Fenestration Rating Council) label standards.

Source: www.Replacement-Windows-n-Shutters.com

Why are Standards important?

Standards ensure products and construction processes meet certain quality and structural integrity requirements. Globalisation also means that materials can now originate from many parts of the world. Mandating minimum safety requirements for materials and construction methods ensures they are of a certain quality and will withstand Australian conditions.

Window and glass standards

All windows and glass used in Australian homes must comply with the following Standards:

• AS2047 Windows in buildings – Selection and installation
• AS1288 Glass in buildings – Selection and installation

Windows made from timber, aluminium, uPVC or other materials undergo the following performance tests to verify product performance claims.

• AS4420.2 Deflection Test – positive and negative wind pressures are applied to the face of the window to test the maximum deflection under wind load.
• AS4420.3 Operating Force Test – verifies that an opening sash is capable of opening and closing without undue effort.
• AS4220.4 Air Infiltration Test – air leakage of a window is tested to ensure energy and acoustic efficiency.
• AS4420.5 Water Penetration Resistance Test – ensures no water leaks through the window into the building.
• AS4420.6 Ultimate Strength Test – negative and positive wind pressures of at least 1.5 times the specified wind pressure are applied to the window to ensure it does not fail in unusual wind conditions.

Question: How do I know that the builder has installed windows and doors in my home that comply with the Building Code of Australia?

Answer: All windows and doors for homes must have a performance label which confirms they are certified to comply with Australian Standard AS2047.

Energy Efficiency Legislation

Across Australia, the energy efficiency bar is being lifted with the rise from a 5 to 6-star energy rating mandatory for all new residential buildings. The requirements of the 2010 Building Code of Australia are designed to improve the performance of Australia’s greenhouse gas emissions. While the commencement date of this legislation differs from state to state (Victoria, Queensland and the ACT have already introduced the code), at some point in the near future all Australian homes will need to meet this minimum level of energy efficiency. Energy ratings apply to the whole building – not just individual elements or materials.

Star Ratings

An energy efficiency star is a measure of how much energy ‘leaks’ through the skin of a building over the course of a year within a given climate. It is an expression of how much artificial heating and cooling energy will be required to keep the inside temperature within a standard ‘comfortable range.’

• 0 stars means the home offers no barrier to the external temperatures
• 10 stars means that the home requires no additional heating or cooling energy

The achievability of star ratings is largely dependent on the climate experienced by the home. For example, the amount of energy lost from a 6-star rated home in Brisbane will be different to (less than) that for a home in Canberra. Generally speaking, compared to other materials used in the building, windows are poor heat insulators and let a lot of radiant heat from the sun into a home. Therefore windows have a big impact on the star rating that can be achieved by a home.

Requirements for existing homes

New energy efficient requirements are also set to affect the sale or lease of existing homes across Australia. Mandatory disclosure requires homeowners to disclose a home’s energy, water and greenhouse performance to prospective buyers and tenants so they can better judge the property’s value. It is expected the measure will be phased in by May 2011, starting with disclosure of energy efficiency. Refer to the government’s National Strategy on Energy Efficiency for more information.

Source: www.Windows.Build.com

The first step in choosing energy efficient windows based on climate, is to understand how the heating and cooling performance of different windows is measured.

U-value

The U-value of a window measures its thermal performance. The lower the U-value of a window the less heat and cold it will conduct, indicating better energy efficiency.

When identifying the U-value of a frame, check this is for the whole window U-value and not just the separate components. A whole window U-value is indicated by Uw whereas the frame on its own is Uf and the glass Ug.

Solar Heat Gain Coefficient (SHGC)

SHGC is a measure of how well a window blocks heat caused by sunlight. SHGC is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits.

Climate zones

The next step in choosing energy efficient windows is to consider your climate and how you can use this to your advantage. Australia can be roughly divided into three climate zones – hot, mixed and cold. Basing your window selection on your specific climate conditions will provide the best energy efficient performance for your home.

Hot climates – Zones 1, 2 & 3

(e.g. Brisbane, Darwin, Northern Australia)

Hot climates require more energy to cool the home. Windows should be designed to keep the heat outside. The best results are achieved by installing windows that limit heat from the sun on all orientations (lowSHGC). Although climate zones one and two are frequently humid while zone three is not, they can all subject the home to the risk of overheating at any time of the year. Good insulation (a low U-value) is also beneficial, especially if the home is air-conditioned.

Hot climate window tips

• Use light coloured frames
• Choose windows with low U-Values and low SHGC
• Choose window styles that provide maximum openable area such as louvres and casement windows
• Locate windows on opposite sides of the building to promote cross ventilation
• Consider high openable windows to maximise air movement
• Make use of shading to reduce solar heat entering the home through clear windows

Mixed climates – Zones 4 & 5

(e.g. Sydney, Adelaide, Perth)

Mixed climates use a relatively even amount of energy throughout the year for heating and cooling. With heat gain required in winter and to be avoided in summer, mixed climates present more design challenges and require some compromises.

West and east facing windows will receive more solar radiation in summer than in winter – the opposite to what is desirable. Choosing windows with a low SHGC and operable shading that can be drawn in summer and opened in winter, will improve performance and comfort year round.

North facing windows receive valuable solar radiation in winter that can heat the home naturally. Choosing windows with mid to high range SHCG will help to harness this free energy.

Mixed climate window tips

• Choose windows with low U-Values
• Choose mid to high range SHGC for north facing windows and low SHGC for east and west facing walls
• Make use of operable shading that can be extended in summer and retracted in winter

Cold climates – Zones 6, 7 & 8

(e.g. Melbourne, Hobart, Canberra)

Cold climates use more energy to heat the home. The objective here is to maximise solar exposure and minimise heat loss for most of the year. Solar heat can be harnessed by locating the majority of windows to the north. Windows with a high SHGC will generally work best as more solar heat is admitted.

U-values are most important in cold climates. There is a greater difference between the indoor and outdoor temperature and choosing windows with low U-values will minimise heat loss.

• Choose windows with low U-values
• Choose windows with high SHGC except for windows that allow unwanted heat gains
• Locate majority of windows to the north – especially in living areas
• Avoid shading windows or use adjustable shading to provide shading only in mid-summer

What U-value and SHGC should I use?

Use the table below as a guide to the preferred U-values and SHGC suitable for your climate. It’s important to remember that U-values and SHGC are just two of the elements to consider in improving your home’s energy efficiency. Other important elements to take into account include elevation, shading and orientation.

Preferred window U-value & SHGC by climate

Choosing the right window

The Window Energy Rating Scheme (WERS) provides comparative energy information on many residential windows available. Windows are rated for their energy performance and illustrated in terms ofcooling and heating stars. No stars show the window is a very poor performer while 10 stars means the best possible performance. WERS-rated windows carry a sticker and certificate specifying their energy performance.

Online search

The WERS website provides an online tool to search for windows by U-value, SHGC and additional criteria if desired. An extensive list of the window systems matching these criteria is provided along with the manufacturers who can supply them.

Snapshot of WERS window information

% – The cooling and heating percentages, indicated by the percentage symbols in blue and red boxes, allow you to compare the products performance compared to a clear, single-glazed, aluminium-frame window.
Uw = The U-value indicates how well the window prevents heat from escaping. The lower the U-value, the better its insulating value.
SHGCw = The Solar Heat Gain Coefficient (SHGC) is a measure of how well a window blocks heat caused by sunlight. SHGC is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits.
Tvw = Visible transmittance indicates how much visible light is transmitted. Tvw is expressed as a number between 0 and 1. The higher the number, the more light is transmitted.
Air Inf = Air infiltration measures how much air will leak through the window. The lower the value, the less air is likely to leak through.

Source: www.Windows.Build.com

Window size has a major impact on the energy efficiency of a building. Large expanses of standard, clear-glazed windows can make a house uncomfortably hot in summer and hard to keep warm on cloudy winter days and nights. The most appropriate size of windows for smart energy design can be guided by building orientation and the amount of thermal mass in the internal building materials.

 

Summer sun is easily shaded.

 

Winter sun admitted.

Orientation

In Australia the sun is orientated towards the north for the most part of the year. To capture the heating benefits of the winter sun place larger windows to the north. In summer, the sun is at a higher angle in the sky so north-facing windows are easily shaded with eaves and awnings.

South facing windows receive no direct sunlight in winter and only early morning and late afternoon sunlight in summer. Keep south facing windows small to reduce heat from escaping during cooler months and reduce heat gain in summer.

East and west facing windows receive little winter, autumn and spring sunlight, but excessive summer sunlight. East and west facing windows should be kept small and well shaded to minimise uncomfortably hot room temperatures in summer and to reduce useful heat escaping in winter.

See window orientation and placement for more information on where to place your windows.

Thermal mass and window size

Thermal mass is the ability of a material to absorb heat energy. A lot of heat energy is required to change the temperature of high density materials like concrete, bricks and tiles. They are therefore said to have high thermal mass. Lightweight materials such as timber have low thermal mass. Appropriate use of thermal mass throughout your home can make a big difference to comfort and heating and cooling bills.

Larger areas of glass are better suited to homes with higher levels of thermal mass and larger north-facing windows. A home with less thermal mass, such as timber flooring, should aim to minimise large areas of ordinary glass. Use the table below to determine the ideal window sizes for your home when using ordinary glass. High performance glazing options increase the size of glass areas possible without reducing energy efficient performance.

Ideal window size based on floor area for standard clear glazing

Acceptable limits

Building regulations will also govern the minimum glass area for rooms. For example in Victoria a minimum glass area of 10% is required for each habitable room. Refer to your local building authority for clarification.

Source: www.Windows.Build.com

Choosing the right Window is a clear way to make your home more energy efficient.
If you are an owner of an older home and are wondering why your electric bills are sky high take a good look at your windows. Older windows were not designed with efficiency in mind.  Swapping out your windows may seem like an expensive daunting task but well worth it in the long run. Air loves to escape through the cracks of old windows. Swapping out your windows for new windows will benefit your monthly electric bill enormously. New windows will help lock the air tight into the comfort of your home, that is what this is all about. So what kind of window should you look for.

You will want to look for triple pane windows! This is one of the best investments you can make on your home. Preferably, gas filled triple pane windows. Be sure to read the label and look for a low U value. Also look for windows which qualify for federal tax credits while they last.

There is some great news for home owners looking to make their home more energy efficient.

Federal Tax Credits are available for homes equipped for efficiency. Although not all Energy Star products will qualify it should be of great concern to check if the product you are considering buying will qualify.

ENERGY STAR distinguishes some aspects of energy efficient products.

Although they may cost more to purchase than standard models, will pay you back in lower energy bills within a reasonable amount of time. (for more information on ENERGY STAR products that are TAX deductible, visit this website: Federal Tax Credit )

On a related note, you will do well to look into Skylight covers if your home has them. Skylight covers are a great way to deflect direct sunlight from heating your home while you are trying to keep it cool.

Making your home energy efficient is worth the effort. A great place to start is by taking a closer look at your household items that can be replaced and your windows make a great place to start.

Source: www.EnergyEfficientHomeTips.com