Windows can be one of your home’s most attractive features. Windows provide views, daylighting, ventilation, and heat from the sun in the winter.
Unfortunately, heat moving in and out of your home through windows can increase your heating and air conditioning bills. Energy efficient windows and measures to reduce heat gain and loss can help save energy and reduce energy bills.
Buying Energy Efficient Windows
Look for the ENERGY STAR® label when buying new windows. Also review ratings from the National Fenestration Rating Council (NFRC). NFRC ratings are included on all ENERGY STAR certified windows and provide a reliable way to determine a window’s energy properties and compare products.
Replacing single-pane windows with double-pane windows that have high-performance glass may be cost effective, but you could also consider installing exterior storm windows. You can obtain energy efficiency ratings for storm windows and other window attachments from the Attachments Energy Rating Council (AERC).
In colder climates consider selecting gas-filled windows with low-e coatings to reduce heat loss. In warmer climates select windows with coatings to reduce heat gain.
U-Factor & Solar Heat Gain
Choose a low U-factor for better thermal resistance in colder climates; the U-factor is the rate at which a window conducts non-solar heat flow.
Look for a low solar heat gain coefficient (SHGC). SHGC is a measure of solar radiation admitted through a window. Low SHGCs reduce heat gain in warm climates.
Select windows with both low U-factors and low SHGCs to maximize energy savings in temperate climates with both cold and hot seasons.
Look for whole-unit U-factors and SHGCs, rather than center-of-glass U-factors and SHGCs. Whole-unit numbers more accurately reflect the energy performance of the entire product.
Have your windows installed by trained professionals according to manufacturer’s instructions; otherwise, your warranty may be void.
Cold Weather Window Tips
- Install tight-fitting, insulating window shades on windows that feel drafty after weatherizing.
- Consider insulated cellular shades, which are “honeycombed” and can be raised or lowered. Obtain energy efficiency ratings for window attachments from the AERC (aercnet.org).
- Close your curtains and shades at night to protect against cold drafts; open them during the day to let in warming sunlight.
- Apply low-e lm on the inside of your windows to keep heat from radiating out. Films are rated by the NFRC and will be rated by the AERC.
- Alternatively, install low-e exterior or interior storm windows, which can save you 12%–33% on heating and cooling costs, depending on the type of window already installed in the home. They should have weatherstripping at all movable joints; be made of strong, durable materials; and have interlocking or overlapping joints.
- Repair and weatherize your current storm windows, if necessary.
Warm Weather Window Tips
- Install white window shades, drapes, or blinds to reflect heat away from the house. It is always best to install exterior shades whenever possible.
- Close curtains on south- and west-facing windows during the day.
- Install awnings on south- and west-facing windows to create shade.
- Apply sun-control or other reflective films on south-facing windows to reduce solar heat gain.