Do Your Replacement Windows Meet Energy Star’s Southern Zone Guidelines?

Do Your Replacement Windows Meet Energy Star’s Southern Zone Guidelines?

The Department of Energy and Environmental Protection Agency teamed up to develop guidelines for optimum window performance in different climate zones of the United States. Down here in the Houston area, we are located in the southern zone. Do your current windows or the replacement windows you plan on buying meet the southern zone recommendations? Find out below.

1. Low U-factor

The U-factor for a window in the southern should be less than or equal to.40. Remember that the U-factor is the rate at which a window conducts non-solar heat. The lower the U-factor, the more energy efficient a window is. A window that meets this recommendation will be able to sufficiently keep heating in on cold days and heat out on hot days. The U-factor of a window is affected by window frame material, glazing (double, triple pane), and Low-E coating.

2. Low Solar-heat Gain Co-efficient

SHGC, for short, is the most important window property in warm climates. The SHGC of a window is the fraction of solar radiation that is admitted through a window and then released into the home. In the southern zone, windows should have an SHGC of .25 or less. The lower the SHGC, the more heat gain is blocked from the sun. A low SHGC can be achieved through a combination of tints, coatings, and glazing.

3. Low Air Leakage

Air leakage (AL) refers to the rate of air movement around a window in the presence of a specific pressure difference across it. Basically, it’s a measure of how much air can get past your window. Windows in the southern zone should have an AL of .30 or less. Air leakage depends on two factors; operation type and installation. For example, windows that slide tend to have a higher AL than windows that are hinged at the top or bottom. If your windows are not properly air sealed during installation, the AL will suffer no matter what type it is.

4. Higher Visible Transmittance

VT is the amount of sunlight that is allowed to pass through the window. A higher VT rating means more sunlight will pass through. In the southern zone, a higher VT is recommended so that you can use the daylight as a natural source of light. The sunlight that comes into your home does not necessarily raise the temperature. Windows with a low SHGC (see above) and a high VT allow sunlight to pass through, but not the heat that comes from solar radiation.

If your current windows do not meet the standards, you can find replacement windows approved for the southern zone at Superior Window Company. Call us today at 281-747-5999 or schedule a free in-home estimate.


We understand the need for reliable and high-quality products when it comes to buying replacement windows for your home, which is exactly why we only offer the very best windows, made by Texans for the Texas climate.

Offering our customers exceptionally high-grade windows they can count on is our number one priority. From our thorough consultation process to custom manufacturing and expert installation, you can count on Superior!

If you are ready to invest in replacement windows that are designed specifically for your Texas home, request your consultation or give us a call today at (281) 747-5999.