Heating Windows

In recent years, window technology has improved dramatically, resulting in lowered energy bills. Some of the most important energy saving features of windows include:

  • multiple layers of glazing,
  • thickness of air space between in double-glazed windows,
  • low conductivity gas fill in sealed insulated glass windows,
  • tinted glass coatings, and
  • low-emissivity (low-e) coatings.

Purchasing Tips

  • When shopping for new windows, look for the National Fenestration Rating Council label; it means the window’s performance has been certified.
  • The lower the U-value, the better the insulation. In colder climates, a U-value of 0.35 or below is recommended. These windows have at least double glazing and low-e coating.
  • In warm climates, where summertime heat gain is the main concern, look for windows with double glazing and spectrally selective coatings that reduce gain.
  • Select windows with air leakage ratings of 0.3 cubic feet per minute or less.
  • In temperate climates with both heating and cooling seasons, select windows with both low U-values and low solar heat gain coefficiency to maximize energy benefits.


  • National Fenestration Rating Council, (301) 589-6374, www.nfrc.org
  • National Wood Window and Door Association, (800) 223-2301, www.nwwda.org
  • American Architectural Manufacturers Association, (847) 303-5664, www.aamanet.org


U.S. Department of the Interior

Greening of the Interior