According to the U.S. Department of Energy, the amount of heat gained and lost through windows accounts for up to 30% of home energy use related to heating and cooling. Estimates on the money you can save vary. But one thing’s for sure—window replacement lowers your utility bills.
Older windows waste energy due to potential air leaks, lack of insulation, and worn caulking and weather stripping. Adding window treatments/coverings, storm windows, or panels can mitigate the problem somewhat. Exterior awnings, blinds, and overhangs can work to some degree, but the most effective way to save energy is replacing existing windows.
More About Energy Efficiency
Modern windows can help lower utility costs due to the following factors:
- Energy Star rating: Each rating pertains to individual climate zones, of which there are four in the contiguous United States. Your climate zone determines the level of insulation needed to maximize energy efficiency. This differs between colder, more variable climate zones in the north and warmer southern zones.
- Low-E glass: Glass coated to prevent penetration of ultraviolet and infrared light, which can fade furniture and other fabrics, wallpaper, and carpeting. While blocking these types of light, it lets in plentiful visible light, which can help warm the interior without adding demand to your heating system, which further reduces costs.
Energy efficiency measures: When it comes to replacement windows, there are two measures to look at. A window’s U-factor indicates a window’s rate of heat loss, while the Solar Heat Gain Coefficient (SHGC) measures a window’s ability to block heat from sunlight; SHGC is more important if your home receives more direct sunlight than shade.
Older windows get colder on the inside surface. You can feel the chill when you touch the glass. On the other hand, the inside glass of an Energy Star certified replacement window stays warm. You can comfortably sit by a window even if it’s freezing outside, without raising the thermostat.
If your rooms are steaming hot in the summer, it may be time for new windows. An Energy Star window that reduces heat gain while allowing in light keeps your home comfortable. You don’t need to turn up the air conditioning, use more energy than necessary, and pay for it.
How Much Can I Save?
It depends on where you live, how you use your utilities, and what you are upgrading. If you’re replacing double-paned windows, you may save somewhat. But if you’re upgrading from single-pane windows, the level of savings will likely be more substantial.
In addition to savings on utility bills, replacement windows can contribute to reducing demand on your heating and cooling system. This saves money because components are less likely to wear out prematurely. You could spend less on maintenance and replacing parts of the system sooner. New windows can help extend the life of your HVAC system.
Selecting Windows for Maximum Energy Savings
For the greatest benefits in cold climates, use gas-filled windows with low-E coatings and a low U-factor; in warm climates, heat-gain-reducing coatings are best, along with windows with a higher U-factor and low SHGC. In general, whole unit U-factors and SHGCs are best. In regions with hot/cold seasons, both should be low to maximize energy savings.