If your windows are drafty, leaking, difficult to open and close or showing other signs of age, it may be time to invest in new, energy-efficient windows to boost both your energy savings and your home’s curb appeal. According to the Department of Energy, The transfer of heat through windows is responsible for up to 25-30% of our home heating and cooling energy use. You can reduce that gain or loss by choosing windows designed to maximize energy-efficiency . But with so many options out there, how do you choose which ones are best for your home?
What Makes Windows Energy-Efficient?
Windows gain or lose heat through air leakage, heat radiation into a home (from the sun) or out of the home (from people and objects inside the home) or conduction of heat, through either the glass panes or window frames. Energy-efficient windows are constructed with materials that minimize heat gain/loss.
- Frame. Vinyl, wood and aluminum are the most common frame materials and provide good insulation. Consider your home’s specific needs and your design preferences and budget. For example, wood may provide the best insulation and can be attractive, particularly in a historic home, but wood may also require more maintenance and may not be the best choice for a humid or rainy climate.
- Panes. The most energy-efficient windows have multiple panes of glass. A double-pane window will insulate much better than a single-pane one. There are also windows available with three or even four panes, although these are more expensive than more common double-pane varieties. Talk to your home improvement contractor to determine if the climate where you live makes the cost for additional panes worthwhile.
- Gas Fill. The area between each window pane is often filled with an odorless, colorless, non-toxic gas, usually argon. This provides better insulation than plain air and increases the window’s energy efficiency.
- Low-E Coatings. Also known as low-emissivity coatings, their application to window glass is used to reflect infrared and ultraviolet light, which keeps heat from escaping in the winter and from entering in the summer. The reflection of UV light also keeps interior furniture and flooring from fading when exposed to sunlight.
- Spacers. These keep a window’s glass panes an appropriate distance apart and help insulate pane edges, reducing the transfer of heat through the window.
Window Efficiency Ratings
How do you know if those fancy-sounding windows will actually save you energy and money? The National Fenestration Rating Council (NFRC) has developed a testing and ratings system to measure and compare the energy efficiency of windows according to the following metrics:
- U-factor: the rate at which a window (or door or skylight) conducts non-solar heat flow. The measure considers all aspects of the window’s construction, including glass and frame material. The lower the U-factor, the more energy-efficient the window.
- Solar heat-gain coefficient (SHGC): the amount of solar radiation coming through the window. The lower the SHGC, the more heat the window will block from coming into your home. The higher the SHGC, the more heat he window will collect and transmit into your home. Depending on the climate where you live, you may prefer a window with a higher or lower SHGC.
- Air leakage: measured in cubic feet per minute per square foot. The lower the rating, the more airtight, assuming proper installation.
- Visible transmittance (VT): the amount of visible sunlight transmitted through the window, measured in a range from 0 to 1. The higher the VT, the more visible light. Your preferred VT amount depends on your home’s daylighting needs. To reduce sun glare, you would want a lower VT.
- Condensation resistance: a measure of how much the window resists condensation on its interior surface. The higher the number, the better the resistance and the less condensation you will see.
When shopping for windows, look for those with the NFRC label, which can only be found on Energy Star qualified windows. The label lists each window’s ratings in the areas above. You may also want to check out the state-specific recommendations provided by the Efficient Windows Collaborative to determine what ratings are ideal for your home.
BGE HOME sells replacement windows with a variety of options to improve your home’s energy efficiency and keep you and your family comfortable year-round. Watch our demonstration of how energy-efficient windows work and contact our Energy & Comfort Consultants to discuss the best options for your home.