What makes a door or window energy efficient? Doors and windows can be a significant source of heat gain and heat loss in a building. This can greatly affect the amount of heating or air conditioning you need to maintain a comfortable living environment. Efficient doors and windows can cut down on your heating and cooling bills.
U-Factor is a measure of the amount of non-solar heat that flows through a window or door unit. Think of it like a measure of the insulating value of the unit itself. A lower U-Factor equates to a better insulating unit.
SHGC (Solar Heat Gain Coefficient) is a measure of the amount of solar radiation that passes through a window or door. The lower the SHGC the lower the amount of radiation and heat transmitted through the unit. In our climate, this generally equates to greater shading and lower air conditioning loads.
Air leakage is the amount of air that can slip past the unit while it is closed. A lower air leakage rating equates to less air leaking past the unit.
When evaluating replacement windows and doors look for the NFRC (National Fenestration Rating Council) label. This will list the U-Factor, Solar Heat Gain coefficient and measure of air-tightness of the unit. These criteria can help you compare one product to another. Energy efficient windows are likely to be double or tripled paned, with insulating gas between the panes of glass. They may also have energy efficient films applied to one side of the glass. Windows and doors that are thermally broken do not allow heat to pass into the home through the window mullions or frames. Doors without glass may have an insulated core.
The energy performance of existing windows and doors can be improved as well. Films may be applied to the glass to reduce solar radiation, and sealing the frames and weather stripping the openings can reduce air leakage. Awnings that shade window openings from the direct sun can also cut down on solar radiation.
Tax credits may still be available to offset the cost of qualified energy efficient doors and windows. Check with the IRS or your tax advisor.