With summer heat on the way, homeowners are thinking about replacing their older windows with new energy efficient windows. Many are also concerned the expense outweighs the benefit. While energy efficient windows don’t save your home as much energy as proper insulation and air sealing, they are important in sealing your home’s envelope, reducing its energy waste, and reducing your energy costs. That’s especially true in the summer because newer Energy Star approved windows are made to lower the amount of heat that gets into your home.
So, knowing how these windows work can help you decide just what kind of energy efficient window you need for your home.
The Right Window in The Right Place
Energy efficient Energy Star windows are designed to reduce heat conduction from the outside into the home (in summer) and the reverse in winter. Heat conduction occurs throughout the window’s surfaces: the frame, glass, and glazing (how the glass is held in place). Windows will perform better than others just because of how they’re built. For example, wooden frames tend to be best at resisting heat conduction, double glazing perform much better than single pane windows, and windows using weatherstripping seal out drafts better than those without.
Energy Star windows are rated in terms of “U-factor” to describe overall heat conduction. The lower U-factor, the better performance. The bulk of the conduction improvement is in the glass. Low-U-rated windows are double glazed with an inert gas (such as argon) between the panes that acts as an insulator. Low-emissivity coatings (Low-e) are applied to the window glass to further reduce heat conduction by up to 50%, making them the most efficent.
Sunshine streaming into your home might be delightful, but not always in summer. Energy efficient windows are also rated on solar heat gain coefficients (SHGC). A high rated SHGC window will reduce transmitting solar heat while a low rated SHGC will allow more solar heat to pass through. That’s a key feature when you are planning window replacements. High rated SHGC windows should be used where there’s a lot of solar heat such as the south and west walls of your home, while low SHGC windows should be used on the eastern and northern walls where there’s less or little solar heat. High SHGC ratings also raise the cost of the window, so it’s better to use them only where you need them.
How Much Can I Save?
Depending where you live and whether you are replacing an old double pane or single pane window, you can expect to save about 7-15% on your energy bills. According to Energy Star, that’s several hundred dollars yearly — but it assumes you replace ALL the old windows in your home. Needless to say, at a minimum price of $100/window alone (a basic vinyl clad 24″ x 36″ Energy Star low-U replacement window ), the price can add up. However, federal tax credits as well as incentives and rebates may be available to reduce the cost.
Ultimately, even if you have just one old window in bad shape, replacing it with a new efficient window will go a long way to improving your home’s comfort and lowering your monthly bill.