Look again. Your windows aren’t the energy suck you might think they are.
You feel cold air coming in through your windows in the winter. That must mean cold air is escaping during the hotter months, too. And that investing in double- or triple-pane windows is your best way to correct the issue and save on energy.
Nope! (And with the cost of replacing your windows, this is surely good news.)
“Don’t blame your windows,” said Laura Matney, Energy Efficiency Programs Manager for Wabash Valley Power Association. “Replacing your windows doesn’t save as much energy as you might think.”
This is true for a few reasons, first of which is basic physics. Windows, even the very best, are never going to prevent as much heat transfer as a wall.
“Even the best windows get only an R-3 rating,” Matney said. (The greater the R-value, the greater the power to keep heat where you want it.) “Even an average insulated wall has an R-11 rating. And a Touchstone Energy Home requires an R-19.”
Compare that to a single-pane, wood-frame window, which has an R-1 rating. An aluminum-framed window comes in with an R-rating of .86. Not great, on either count when compared to walls (which, on the downside, are terrible at providing views), but not much lower than even a triple-pane window.
You can improve the heat retention of your window significantly just by adding storm windows. Doing so bumps up your single-pane windows nearly to triple-pane efficiency.
Even simpler? Add curtains, especially those that are fairly thick. Keep them closed when the sun is down and open when it’s up to get the greatest benefit during the cooler months. And keep them closed during the hottest part of the day if you’re trying to keep heat out in the summertime. Window films also help reduce heat transfer; blinds and shades do the same but are most effective when it comes to blocking sun during hotter months.
Given that the gap between best and worst windows is so small, justifying the cost of new windows is tough. Depending on the kind of home heating system you use and the number of windows you have, expect it to take between 10-30 years to recoup your investment in energy savings.
But there’s even more to the story: Your windows might not even be your problem.
“People often tell me they have leaky windows,” Matney said. “But in all the years I’ve gone into homes for energy assessments, only one or two were actually found with a blower door test to have leaky windows.”
The confusion arises because of how air moves within a house. Heat moves to areas of lesser heat. (”What?” you say. “Heat doesn’t rise?” Nope, warm air rises. Heat moves to cold, even if that cold is down instead of up.) So the natural air movement in a house gives you the impression that the windows are leaking simply because they do pull the warmed air their way. Even a triple-pane window doesn’t have the insulation value to completely stop that movement. (But, again, curtains will help reduce it.)
“New windows are rarely the answer that gives you the most energy savings,” Matney said. “If you’re building a new house, then by all means buy the best windows you can afford. But if you’re thinking of replacing the windows you have, you can get more bang for your buck by investing in insulation and sealing. Your local Energy Advisor can give you more information about finding ways to save.”