Every window dealer says they have the best windows on the market. They can’t all be right.
So how do you know what to buy? Here are the basics.
Start with your mission
Before buying windows, or any home improvement, decide your mission. For your dream home, you want the best of the best. For a rental unit, you may not care as much.
Ask for the data sheet
Most manufacturers have an Architectural Data Sheet. It isn’t always handed to consumers, so ask.
My opinion: if you can’t get the data, don’t buy the window, or at least don’t buy it because of what a salesperson said. Base your decision on just two things: the data and how it looks. If you don’t like the look, you’ll never be happy.
What to look for
Glass. Whatever brand you buy, the glass will most likely come from Cardinal, Guardian or Vitro (formerly PPG). They’re the best. If it doesn’t, make sure it’s close in quality.
Panes and glass thickness. Standard window glass is “single strength” (about 3/32″) or “double strength” (about 1/8″). Thicker glass, like 1/4″, is stronger and quieter, and multiple panes help even more.
Laminated glass. Two or more layers of glass bonded to a plastic interlayer. If it breaks, it holds together instead of shattering. That means better security, better storm protection and less noise.
IGU (Insulated Glass Unit). How the panes are “sandwiched,” usually called double or triple glazed. Between the layers is air or an insulating gas, sealed at the edges, all to cut heat transfer.
The NFRC label. Look for the National Fenestration Rating Council sticker. It gives you independently tested numbers for the whole window, frame included. These are the ones that matter:
U-factor. How much heat escapes. Lower is better. ENERGY STAR windows typically run about 0.20 to 0.30, and in a cold climate like Colorado you want roughly 0.22 or lower. A window rated 0.22 beats one rated 0.30.
R-value. The flip side of U-factor (R = 1 ÷ U). Higher is better. Don’t expect wall-insulation numbers: a typical double-pane window is roughly R-2 to R-4, and a good triple-pane can do better.
- Low-E is a microscopically thin coating that reflects heat: out in summer, in during winter.
- Gas fill (usually argon or krypton) insulates better than air, but some can slowly leak out over the years.
SHGC (Solar Heat Gain Coefficient). How much solar heat gets through, on a scale of 0 to 1. Lower means less heat. A high SHGC can give you free heat in winter but overheat you in summer. Balance it with your climate, window direction and shade.
VT (Visible Transmittance). How much daylight gets through, from 0 to 1. Higher means more light.
Air leakage. Also on many NFRC labels. Lower is better: it means fewer drafts.
Frames. I recommend vinyl above all else, with fiberglass a close second. I don’t like wood because of the maintenance. If you must go wood, get exterior aluminum-clad windows to cut down on weather wear and painting.
Vinyl. It comes recycled (ground up and reconstituted) or pure virgin vinyl. Pure is best.
Construction. You can see and feel it. Corners should be neat and smooth, and fusion welded (heated and pressed together). Test their strength. Rails should be extruded or die-cast, with plenty of air chambers for strength, durability and insulation.
Performance grade (PG). Windows are tested under the North American standard AAMA/WDMA/CSA 101/I.S.2/A440 (AAMA is now part of FGIA). The rating shows a performance class (R, LC, CW or AW, from residential up to architectural) and a performance grade (PG) in pounds per square foot. That’s the wind pressure the window can take while still keeping out water and air. Higher PG = stronger window. Most homes do fine around PG 30 to 50. Higher-wind areas need more.
STC (Sound Transmission Class). Higher means a quieter window. Ordinary double-pane windows land around the high 20s to low 30s. Laminated glass and mismatched pane thicknesses push it higher.
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