A home’s doors are responsible for a significant portion of its heat gains and losses, so it is important to know how to identify a door’s efficiency rating and how it applies to your own home. There are many different metrics that can be used to determine a door’s efficiency rating and several different organizations that assign ratings based on those values. We will take a look at each particular value in turn and analyze what it means for homeowners.
U-factor and R-value
U-factor and R-value are two values that measure how well the door conducts heat in two different ways. A low U-factor and a high R-value mean a door is well insulated and allows little heat through, while a high U-factor and a low R-value mean that the door is poorly insulated. You can convert between the two by dividing one by either one of the values to get the other. U-factors range from as low as 0.1 to over one, while R-values usually fall between one and 10. Keep in mind that a door with a window in it would have a separate U-factor for the window itself and an R-value for the door.
Solar Heat Gain Coefficient
Solar Heat Gain Coefficient – SHGC – measures how much of the sun’s heat a door or window lets through. It ranges from zero to one, with no solar heat being allowed in at 0 and no difference from being outside at one. In warmer climates, a lower SHGC is preferred to save on air conditioning costs. However in colder climates where heating is required more often than cooling, a high SHGC is more helpful.
Air Leakage
Air leakage measures how much air flows between the interior and exterior sides of the door when it is tightly shut. The lower the value, the less air is let through. While the effect of this airflow is already included in the door’s R-value, it could be an important measurement when considering allergies or inclement weather.
Condensation Resistance
Condensation resistance measures exactly that – how much condensation forms on the door when its interior and exterior are at different temperatures. This is an important measurement in hot and humid climates. It is measured from 0 (worst) to 100 (best), with most modern doors closer to 100 in value.
Visible Transmittance
Visible transmittance measures how much light the door or window lets through and how much is absorbed by the glass. Fully opaque glass has a value of zero, while perfectly transparent glass has a value of one. The higher this value, the more sunlight the room behind the door will get.
Energy Star Rating
There are many values that measure a door’s efficiency, so it can be difficult to decide on the right one. The US Department of Energy’s Energy Star rating looks at the U-factor and the Solar Heat Gain Coefficient of a door or window and, should they meet its criteria, assigns it a recommended climate zone. There are four different Energy Star climate zones in the United States based on the amount of heating and cooling necessary, so be sure to pick the door that is recommended for your climate.
Many Choices
Even with Energy Star recommendations, it can be difficult to find the best door for all circumstances. The importance of each of the different efficiency ratings to your home depends on the local climate as well as your specific efficiency needs. By understanding the meaning of these efficiency statistics, you can make an informed choice on which door is right for you.
Related Resource: Weather Stripping for Windows
