When selecting new windows for your home, I bet you haven’t considered the window condensation rating of the product. You’re not alone, most home owners are unaware that the National Fenestration Rating Council (NFRC) even has a window condensation rating system. You may be familiar with the more common elements of the NFRC rating system such as the U-Factor, the Solar Head Gain Coefficient rating, the Air Leakage rating, and even the Visible Transmittance rating. But the average Joe (no offence if your name is Joe) hasn’t even thought about window condensation, while making the assumption that all windows are created equal in this department. Wrong!
Why do we Care About Window Condensation Ratings
If you ignore the condensation rating of your new windows, you may regret it down the road. For all homes constructed in a climate zone that has a heating season, condensation is a major concern. The formation of excessive condensation on the inside of your home windows can lead to damage throughout your home. The extreme moisture can harm curtains, drywall, window moldings, adjacent carpets, and even the window itself. If nothing else, you don’t want to deal with the restricted visibility should condensation occur.
What is Condensation
Without getting too technical, condensation is simply the formation of water or frost on the surface of the window. Condensation occurs when the temperature of the window is below the dew point. For instance, if the interior temperature of your windows is 45 degrees Fahrenheit while the dewpoint is 55 degrees, water droplets will begin to form on the inside of your windows.
Reducing Window Condensation
To combat window condensation, you need to keep the interior temperature of your windows above the dewpoint. This may be easier said than done, but manufacturers of high-quality windows have accomplished this feat by reducing the amount of heat transfer through their windows. This is called the U-Factor, also known as the thermal transmittance rating of the window. The U-Factor range for most residential windows is from 0.20 to 1.20. The lower the number the better the window is at keeping the heat inside your home, and therefore reducing the amount of condensation on the glass.
NFRC Window Condensation Ratings
The window condensation resistance rating is an optional notation on the NFRC Window Rating label. For those products that feature this information, the condensation resistance is the measurement of how well the window assembly combats the formation of condensation on the inside of the glass. The scale ranges from 1 to 100. The higher the number, the better the window will resist the formation of condensation.