Considerations for Selecting Energy Efficient Windows for Homes in Different Climates

Reviewed and Revised on 11/13/2013

It is very important that you consider your climate when selecting energy efficient windows to reduce home energy use. One size or type does not fit all homes and climate zones.

Window energy efficiency criteria for different climates

• In temperate climates with both heating and cooling seasons, select windows with both a low solar heat gain coefficient (SHGC) and a low U-factor to maximize energy benefits and savings.

• For cold or very cold climates where home heating is the major energy use the focus should be on finding a window with a low U-factor. U-factors of 0.35 are recommended and often required in building codes, but U-factors may be as low as 0.15. In addition, select windows with spectrally selective coatings to reduce heat gain and windows that are gas filled with low emissivity (low-e) coatings on the glass to reduce heat loss. According to the U.S. Department of Energy (DOE), moderate solar gain low-e coatings of 40 to 55 typically are selected for northern and mixed climates where winters are cold and summers moderately hot. In cold climates, the low-e coatings are applied in the window space to the glass surface facing the living area.

• For south-facing windows, US DOE suggests a solar heat gain coefficient (SHGC) of 0.60 or higher to maximize solar heat gain during the winter. East and west facing windows should have a lower SHGC and be shaded.

• In cooling-dominated or warm to hot climates, look for a low SHGC at or below 40%. Buy products with low SHGCs to reduce unwanted heat gain. The U.S. DOE recommends windows with low-e coatings on the glass to reflect some of the sunlight, keeping your rooms cooler.

Windows with low-e coatings, especially spectrally selective coatings, reduce summer heat gain and air conditioning costs without reducing visible light. For hot climates, the low-e coating is applied to the interior of the outside glass (glass facing outdoors) and are used especially on east and west facing windows and unshaded south facing windows. Apply sun-control or other reflective films on south-facing windows to reduce solar gain when there are no extended awnings or exterior shading.

Select quality energy efficient windows in any climate Windows should have weatherstripping at all movable joints, be made of strong, durable materials, have interlocking or overlapping joints and warm-edge spacers between the window glazing. Low-e storm windows save even more energy. Select windows with air leakage ratings of 0.3 cubic feet per minute or less. Look for the ENERGY STAR® label and the National Fenestration Rating Council’s label to help you chose the window for the climate, the house structure and the household’s needs.

U.S. DOE Building America Recommended U-Factors and Solar Heat Gain Coefficient as Best Practices for Various U.S. Climates

U.S. Climate Region	U-Factor	Solar Heat Gain Coefficient
Marine Climate	0.35 or lower	0.35 or lower
Hot Humid	0.35	0.35
Mixed Humid	0.40	0.40
Hot Dry and Mixed Dry	0.30 or lower	0.30 or lower
Cold & Very Cold	0.35	0.35

Source: Building America’s Best Practices Series available at Building America Publications.