At ProActive Energy Systems we offer a free energy audit to home owners in the Raleigh Durham area. During this audit we look for the areas where a home owner can get the greatest result in energy efficiency for the least amount of investment.
Frequently we are asked about the cost effectiveness of replacing old windows. In spite of all of the hype and wild claims about replacement windows saving energy, new windows are frequently very low on my priority list for home owners who wish to reduce their energy consumption. Often our customers are surprised to learn that their windows are really not that leaky (as proven by the blower door test). I contend that replacing windows in your house before you air seal and insulate the attic is kind of like replacing the washer on a garden hose that you just ran over with your lawn mower. The washer will do nothing to stop water loss from the cut up hose. Your best plan would, of course, be to splice the damaged hose first, then replace the washer if you saw water leaking from the connection.
Most building performance studies have shown that the first step in energy efficiency begins in the attic. As a general rule about 60% of a homes energy is lost through the attic while only 30 percent is lost through the walls, windows and doors. A leaky attic will allow rising warm air to escape. As warm air escapes through the attic, colder outside “make up” air will be drawn into the building below the attic. This is the so called “stack effect.” Since much of the leakage attributed to a window is from the area around the window rather than the window itself once the top plates of the wall are sealed in the attic, the window is often no longer a problem area.
Other building science organizations have also found that windows are not the energy robbers they were once thought to be. Consider what Arnie Katz of Advanced Energy out of Raleigh, NC has to say about windows. Advanced Energy is a non-profit organization with connections to North Carolina State University. They have no reason to overstate or understate the effectiveness of any energy efficiency interventions since they are dedicated to research and consultations.
“So first, let’s get rid of one of the big myths out there: In most existing homes, replacing the windows is not a high priority for saving energy.”
Consider also that a single pane window has an R value of “1.” R values are a measure of the ability of a material to block the flow of heat. A new high efficiency window may have an R value of 2 or 3. This is a very small increase compared to what can be done in the attic where a typical inefficient home may have only enough insulation to create an R value of 19 but we can easily raise that R value to 40 or 50. Doesn’t it make more sense to spend your hard earned money raising your attic more than 20 R value points compared to spending money raising your windows only 1 or 2 R value points?
Why then do so many homeowners believe that the windows are the culprit causing high energy bills? In my personal opinion I believe the window industry itself has propagated a lot of misleading information. A quick internet search will reveal many window companies claiming energy use reductions of 30%. Consider again what Advanced Energy has found in their research of energy efficient buildings.
” If your total utility bill (gas and electric) is $2,000 a year, approximately $1,000 of that will be for heating and cooling. Approximately $200 of that is caused by heat loss or gain through the windows. Good, new energy efficient windows can save you 50 percent of that, or $100 a year.”
So a typical new array of windows will save a homeowner about $100 per year while adding insulation, attic air sealing and duct sealing will save about 3-5 times that amount at a fraction of the cost of replacing the windows.
To be very clear, windows are indeed an important part of a homes building envelope and for a house to be as energy efficient as possible, the windows must also be efficient. The point here is that windows are rarely the “biggest bang for the buck” when it comes to home energy efficiency and comfort. Instead, ask a professional energy auditor in your area for a consultation. If you live in the central North Carolina area we would be happy to provide this service for free. Otherwise you can consult the Building Performance Institute for a professional in your area.
