Do Your Dallas/Ft. Worth Replacement Windows Pass The “Miles-Per-Gallon” Test?
If They’re 10 Years Old Or Older, Probably Not!
If you’ve been interested in replacement window installation in Dallas or Fort Worth, you may have been told U-Factor or Solar Heat Gain Coefficient (SHGC) is the most important thing to look for when shopping for windows.
Northern areas like to focus on U-Factor and Southern areas like to focus on SHGC. The truth is BOTH are important.
U-Factor is an insulative measurement which is why with a simple mathematical formula you can convert U-Factor to an R-Value (1/U- Factor = R-Value). Solar Heat Gain Coefficient (SHGC) is a reflective measurement, measuring how much solar heat is reflected. The decimal percentage measures how much heat passes through.
An easy way to relate these measurements is compare it to your attic. SHGC working like radiant barrier and U-Factor working like attic insulation. They both work in different ways and they are both important.
SHGC is the rate at which radiant heat, the heat that accompanies light from the sun, penetrates through a window. This rate is expressed as a number between 0 and 1. The lower the SHGC, the better the window is at blocking heat.
According to Efficient Windows Collaborative, which is sponsored by the Department of Energy, the ideal window for Dallas and Fort Worth should have a SHGC of less than or equal to 0.27.
You may be thinking, “But won’t blocking out heat also keep out sunlight?”
The answer to this question used to be Yes. (Shade screens, for example, cut down heat by reducing a corresponding amount of light.) But Low-E technology has changed that.
Low-E consists of one or more microscopic coatings of silver applied to glass (in Texas it should be applied to the inside of the outer pane of insulated glass). The great thing about Low E is that it’s “spectrally selective” — it can differentiate between longer wavelengths (the heat portion) and shorter wavelengths (the light portion). This technology REFLECTS the former while letting the latter pass through. This, in turn, gives you the best of both worlds: maximum light with minimal warming effect.
When you want to determine how much light a window will let in, you need to look at its Visible Transmittance (VT) rating. This rating is express as a number between 0 and 1, with most windows falling between 0.3 and 0.7. But unlike SHGC, the higher a window’s VT rating, the better.
Remember: You want a low SHGC and a high VT.
What About The Other Factors?
Though most people tell you this is not as important SHGC, this would be like saying that better insulation isn’t that important.
The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly, expressed between 0 and 1. The lower the number, the better. The lower the U-factor, the greater a window's RESISTANCE to heat flow and the better its INSULATING properties.
Air Leakage (AL)
AL is the rate at which cubic feet of air passes through square foot of window area, expressed between 0 and 1. The lower the AL, the less air will pass through cracks in the assembly. AL is just as important as U-Factor and SHGC but is an optional measurement on the NFRC label. Generally, though, a rating of 0.3 or lower is considered acceptable. Even though NFRC does not list lower than a 0.1 on the label and most windows don’t list their numbers, our Quantum 2 window has an AL of 0.02.
Condensation Resistance (CR)
CR measures how well a window resists condensation on the inside surface. CR is expressed as a number between 1 and 100. The higher the number, the better. Fifty to 60 is considered average, while anything above 60 is considered good. (CR is also an optional rating, and does not appear on some NFRC labels.)
Clarity Windows, Bring Clarity to your home!
The home improvement experts at Clarity Windows are ready to help you reduce energy costs and make your home more beautiful and comfortable. Contact us for a free estimate today by calling (888) 458-3630, or completing our on-line quote request form.