Arizona Home Inspection Window Label

Window labels are full of valuable information but the trick is to know what each of those numbers mean. Is a high number good as in football or basketball, or is a high number bad as in golf? Hopefully by the time you finish reading this short article you will have a little better understanding of what each of those numbers mean. If you are having a home built or thinking about having your windows replaced, it would be a good idea to maybe print this page and take it with you to your window provider. It is alarming at how many people sell windows and do not actually know how to read a window label such as the one below. We are going to break each one of those numbers down to get a better understanding of them.

U-Factor

The U-Factor is the rate of heat loss in terms of the U-factor (U-Value). The lower the U-factor, the greater a window’s resistance to heat flow meaning it has a better insulating value. For Example: during the winter months when it is 50 degrees outside and it is 70-75 degrees indoors and you have a window with a low U-factor it is easier for the heated air on the inside to escape to the outside through the glass. If you raise the U-factor on the glass it gets harder and harder for the heated air to escape keeping your house nice and warm and being more energy efficient.

In Maricopa County located in Arizona where we are mostly cooling, the recommended U-factor number should be Less than or equal to 0.60. A low U-factor is useful during cold days when heating is needed. A low U-factor is also helpful during hot days when it is important to keep the heat out, but it is less important than the SHGC in warm climates such as in Maricopa County in Arizona.

Solar Heat Gain Coefficient (SHGC)

The SHGC is the fraction of incident solar radiation admitted through a window.SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits. Whether a higher or lower SHGC is desirable depends on the climate,orientation, shading conditions, and other factors. For us that do not know alot about windows, solar heat is heat that is generated from the sun and the SHGC number explains how much of that heat from the sun actually penetrates to the inside of the house through the window.

In Maricopa County located in Arizona where we are mostly cooling, the recommended SHGC number should be Less than or equal to 0.27. A low SHGC is the most important window property in Hot climates such as in Maricopa County Arizona.

Visible Transmittance (VT)

The VT is an optical property that indicates the amount of visible light transmitted. VT is a whole window rating and includes the impact of the frame which does not transmit any visible light. While VT theoretically varies between 0 and 1, most values are between 0.3 and 0.7. The higher the VT, the more light is transmitted.

Air Leakage (AL)

AL is expressed in cubic feet of air passing through a square foot of window area (cfm/sf). The lower the AL, the less air will pass through cracks in the assembly. AL is very important, but not as important as U-factor and SHGC. AL is an optional rating on the NFRC label.

Condensation Resisitance (CR)

CR measures how well a window resists the formation of condensation on the inside surface. CR is expressed as a number between 1 and 100. The higher the number, the better a product is able to resist condensation. CR is meant to compare products and their potential for condensation formation. CR is an optional rating on the NFRC label.”