Should I Replace My Old Windows?
When people think of insulating their home, often the first thing that comes to mind is replacing windows. However, home energy auditors often say wait.
The reason is that new windows tend to be expensive compared to taking simpler steps, like sealing air leaks. A set of old single-pane windows might be the most visible energy wasters in your house, but that hidden leak in your attic or basement could be losing a lot more heat.
There is also embedded energy to consider. Windows are made of glass, which requires a lot of heat to manufacture, which in turn releases a lot of carbon into the atmosphere. In other words, it might take quite some time to recoup the energy used in making a new set of windows in the form of lower heating and cooling bills.
What We Chose
For people who have already taken care of all the relatively inexpensive retrofits, or for those building a new house, as we did, upgrading windows can make a tremendous difference.
As with the rest of the systems in our house, we had three objectives when we chose our windows: performance, durability, and low cost.
Our window package was manufactured by a company called Vinyltek, located about 20 minutes north of the border in British Columbia. Although the company is relatively new to the Washington market, they have been making windows for more than 25 years.
We knew we needed triple-glazed windows to achieve our net-zero-energy goal, but our budget limited our choice of materials. Triple-pane windows with fiberglass or wood frames were clearly out of our price range. Vinyl is much lower cost, but often doesn’t perform as well. The triple-pane windows we chose, however, had a lot of extruded internal chambers that provide outstanding insulation, allowing them to outperform all but the most expensive windows on the market.
Another important consideration was the coating on the glass, which helps reflect the heat back into the house, while allowing solar energy to pass through and passively heat the house.
What to Look for in a Window
The main factor to look for when shopping for windows is U-value, which tells you how good a window is at reducing heat loss. The lower the number, the better the window is at insulating. Here in cool-to-mild Seattle, you’ll also want to consider a window’s Solar Heat Gain Coefficient (SHGC), which tells you how much solar energy a window allows to pass through to help heat your house during the day.
Our windows are rated at .15 – .21 U-value, which is very low, especially considering their moderate cost. Our Solar Heat Gain Coefficient (SHGC) is .50, meaning they let in a ton of solar energy, despite their low U-value. (It can be hard to have both low U-value and high SHGC, but improvements in glass coatings and the argon gas they use to fill the spaces between the glass make it possible.)
Here’s a great guide from the Efficient Windows Collaborative.
You can also check out vinyltek.com.