Do Your Windows Pass The “Miles-Per-Gallon” Test?

(If They’re 10 Years Old Or Older, Probably Not!)


Windows MPG

A car’s fuel efficiency is measure on how many miles per gallon it gets. A window’s energy efficiency is measured in the same vein. A number of factors are used to determine the energy efficiency of a window. These include the following: U-Factor, Solar Heat Gain Coefficient, Visible Transmittance, Air Leakage, and Condensation Resistance.

The good news is that it’s extremely easy to determine how energy efficient a window is: Everything you need to know is on Energy Star’s NFRC label found on a window. This label shows exactly what kind of energy performance you can expect from the window and is the only measurement accepted by the U.S. Department of Energy’s Energy Star program.

One of the most important ratings on the NFRC label is the U-Factor. U-Factor measures the rate of heat loss between 0 and 1. The lower the U-Factor number, the better the window keeps heat in your home. A well-insulated window with a low U-Factor is going to keep your home a comfortable temperature year round, while cutting your energy costs. In Colorado even though we have 350 days of sunshine we still have more days where the temperature is 60 degrees or less then we do 90 Degrees or higher on average. So the U-factor is a very important benchmark to keep in mind.

According to Efficient Windows CollaborativeColorado homeowners want a window with a U-Factor of 0.30 or less.

Consider windows eight years and older have an average U-Factor of 0.45, and you’ll see just how much more energy efficient new windows are. Since you can save approximately $30 per year in energy costs for every .01 you lower the U-Factor of your windows, you’d be keeping at least $390 in your bank account every year and with our TRIPLE pane windows you can save even more, maybe enough for a well-deserved vacation!

What About The Other Factors?

You should also consider the following features on the NFRC label when you’re shopping for new windows.

Visible Transmittance (VT)

VT measures the amount of light that can enter a window on a scale of 0 to 1. In the case of VT, the higher the rating, the better. Most windows are between 0.3 and 0.7.

Solar Heat Gain Coefficient (SHCG)

SHGC measures how well a window blocks out heat on a scale of 0 to 1. The lower the number, the more heat the window blocks. SHGC is more important in hot climates like Arizona, where the temperatures reach well over 100 degrees. Just know a good SHGC is 0.4 or less.

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 isn’t as important as U-Factor and SHGC and is an optional measurement on the NFRC label. Generally, though, a rating of 0.3 or lower is considered good.

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.)

If you’d like more information on window energy efficiency, contact us today.