One of the ways to make your home more eco-friendly is to replace old windows. When I moved into my house, we found that our living rooms windows were the original windows that were put in in 1938. Needless to say, these windows were quickly replaced. However, picking out new eco-friendly windows is a tad harder than it looks on the surface. Besides the personal choices you make with a window (type and style), you need to understand the ratings each window has. The ratings help you to evaluate the insulating properties. The majority of window makers (Andersen, Hurd, Jeld-Wen, Pella, etc) use this system. The NFRC (National Fenestration Rating Council) website lists over 100,000 windows in their Certified Products Directory. They rate the entire package too – glass and frame. Now, all windows may not have the rating label on them. It does not mean that they aren’t eco-friendly. However, you just have no way to compare it to those who are.
Now, deciphering the labels is not as scary as it seems. The first thing you will see on the label is the manufacturer and model and the type of operation (double-hung, casement, etc). There should also be a description of the frame and the glazing. If it says something about cladding, that just means that there is a covering on the exterior frame that provides more protection. It requires less maintenance than paint. If it says your window is double glazed, that just means that there are two panes of glass filled with a gas like argon that provides an insulating barrier.
Next, there is the U-Factor. This is an important rating. It measures the energy efficiency for the glass and the frame. The lower the number, the better. You are wanting a window rated between 1.2 and 0.2.
The SHGC (solar heat gain coefficient) is how much solar heat is absorbed by a window and transferred into the house. The lower the better.
The VT rating (visible transmittance) is how much light that comes through the glass. It will between 0 and 1, and the higher the number the better. It is actually one of the least important numbers, because to the majority of the people, you can’t tell the difference.
You also want a low number in the air leakage category. This rates the cubic feet of air passing through a square foot of window area bu the way of cracks in the window assembly. However, this does not take into account any gaps between the frame and the siding.
Lastly, there is the condensation resistance. Not all manufacturers include this number. It is a number between 0 and 100 and rates the ability of the interior surface to resist the formation of condensation. The higher this number, the better.
All windows are not created equal. Hopefully, this will help you find the perfect windows for your eco-friendly home.