Keep Energy From Going Out The Window

February 22, 2011


Windows, and the hot and cold air lost through them, can make up 10 to 20 percent of the average homeowner’s energy bill.  However, there are some things you can do to cut down on the loss of conditioned air in your home, short of replacing all the windows.

The loss of heat in the winter and the gaining of it in summer can be attributed to three main causes: the conduction of heat through the glass or frame of the window, radiation of heat into or out of the house, and air leakage.  These problems can be fixed or mitigated by weatherization and/or repair of the window system, and the use of shading devices.


  • Use heavy-duty, clear plastic on a frame or tape clear plastic film inside window frames during winter months.  The plastic must be sealed tightly to the frame.
  • Install interior or exterior storm windows – they can reduce heat loss through windows by 25-50%.  Low-e storm windows can save even more energy.
  • Repair and weatherize current storm windows.  Make sure they have weatherstripping at all movable joints, are not broken, and that all windows fit properly.

Shading Devices

  • Install tight-fitting, insulating window shades on windows that feel drafty after weatherization.
  • Close curtains and shades at night and open them during the day.
  • Clean windows on south side of house to let in winter sun.
  • Install white shades, drapes, or blinds to reflect heat away from your house.
  • Close curtains on south and west side windows during the day to reduce heat gain.
  • Install awnings on south and west side windows.
  • Apply low-e or other reflective films on south windows to reduce solar heat gain.

Of course, it may just be time to invest in some new windows.  If this is the case, here are some key items to look for:

  • Look for National Fenestration Rating Council labels.  This means the performance of the window has been certified.
  • Lower U-value windows provide better insulation.  In cold climates, look for values below 0.35.  Windows should be at least double glazed and have a low-e coating.
  • The air leakage rating should be below 0.3 cubic feet per minute.
  • Use reputable, qualified installers.  Proper installation is required to avoid air leaks around the frame.
  • Look for Energy Star and EnergyGuide labels.

For more information on saving money through windows, check out

Photo courtesy of Liz West through a Creative Commons License.



Dawn Killough

has over 15 years experience in the construction industry and is the author of Green Building Design 101, an e-book available from Amazon. She is a LEED AP and Certified Green Building Advisor, and has worked on the LEED Certification of three projects in Salem, Oregon.