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