Careful selection of windows balances heat loss and solar heat gain. Both type and construction of windows needs to be considered. Not all windows need to open. Fixed windows allow no air leakage. For situations where windows need to open, casement and awning windows provide the best long-term air tightness.

Passive Solar Windows InteriorDouble pane "Low-E" glass, which provides an insulation value of around R-3, is the minimum window glazing choice recommended for cold climates. By blocking radiant heat loss, low-e glass also inhibits passive solar gain. In passive solar homes, the glazing should be selected for each side of the building in order to optimize internal heat loss and solar heat gain. 

Because of superior insulation and air tightness in the roof and walls, it is not uncommon for more than 50 percent of the heat loss in a SunTerra home to occur through the windows. Choosing window coverings with a high insulating value to reduce heating cost and further improve comfort. If you choose a window covering that has an R-3 insulation value, you could reduce the heat loss of your home by 25 percent when window coverings are drawn.


Window Type


Double Pane

Double Pane
Air Low-E

Double Pane
Argon Low-E

Triple Pane
Argon Low-E

Picture Unit  .50 .33 .29 .20
Casement and Awning .46 .33 .30 .23
Single Hung * .50 .35 .31 .24
Horizontal Slider * .50 .35 .31 .24
Patio Door * .50 .36 .33 .29

 The smaller the U-Value number, the more efficient the window.

 * Not recommended for Energy-Efficient Homes


Exterior of green SunTerra home