ATTENTION RESIDENTS OF SOUTHERN ARIZONA:

You May Be Losing Up To $346 On Your Energy Bills Per Year Because Of Bad Windows!

You Need to Read These Facts about Solar Heat Gain Coefficient
Right Now, So You Can Prevent Your Windows From
Hemorrhaging More Of Your Money.

You may have heard that U-factor is the most important thing to look for when shopping for windows.

While this is true for colder parts of the country, U-factor is not what’s most important in hotter states like ours.

This is because U-factor measures the rate of heat loss (in BTU’s per hour) through glass or other materials in wintertime. And while it’s true we want to keep our homes warm during the few months when it’s cold outside, the much bigger problem is keeping them cool during the long, sweltering summer months.

Since we live in a warm climate, Solar Heat Gain Coefficient (SHGC) is the number one thing you must look for when window shopping.

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 southern Arizona
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 southern Arizona 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 wave lengths (the heat portion) and shorter wavelengths (the light portion). This technology blocks 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.