Windows are one of my favorite topics. I love windows. I have lots of them. I like to feel like I am outside. If I had 100 acres, I’d build a glass house right in the middle.
Windows today are much more efficient than they were ten years ago. If you have the inclination and the means to replace your old ones, do! When I remodeled two years ago, I replaced about 2/3 of my windows, and it made a huge difference in my heating bill.
Today’s windows are made for the different orientations in your home. Some keep heat out, some let it in. Also take into consideration views you want to take in or block, natural lighting and furniture placement.
When you are shopping for windows, this information will tell you about window performance:
• U-factor rating of the National Fenestration Rating Council (NFRC) – the lower the number, the more efficient the window, based on the glass, frame and spacer material.
• Solar Heat Gain Coefficient (SHGC) – This figure lets you know how much heat a window transmits. For passive solar gain, this number should be higher than .6. For windows on the north side that let sun in during the summer, this number should be lower to block the heat.
• Visible Transmittance (VT) – This number, between 0-1, states how much light comes through a window. For passive solar, this number should be high.
• Low-e – low-emissivity. A thin, invisible coating on the glass controls the amount of heat moving through it in both directions, in and out. This affects the U-factor and the SHGC. Low-e windows can save you 30-50% on your energy bills.
For passive solar applications, you want:
• A high SHGC
• A low U-factor
• A high VT
• Low-e windows
For northern orientation, you want:
• A low SHGC
• A low U-factor
• A low VT
• Low-e windows
Talk to a reputable window distributor, read the labels on the windows, and check out these websites for more information – www.energysavers.gov and the website of the NFRC, www.nfrc.org.
{ 2 comments… read them below or add one }
Nan–this is good information, and sorry I didn’t see this post sooner, but amidst the current barrage of window manufacturer advertising, it is also important to note a few things:
1. Windows, even the most energy efficient on the market today like those from Serious Materials, are still typically the weakest link in the overall building envelope.
2. Windows are in a state of rapid innovation right now, and many experts agree that their energy efficiency properties will improve dramatically in the next several years.
3. Quality windows are expensive, often at more than $1000 each.
4. For bang for the buck, there are almost always more cost effective ways to permanently reduce energy use–like air sealing and insulation.
Thanks, Peter! Great info! :)