Infiltration. Conduction. Radiation. If you are at all considering switching to or installing energy-efficient windows you need to know the meaning of these three terms and how they effect you and your wallet. Just because a window manufacturer claims their windows to be energy-efficient doesn’t make them so as windows have ratings as to just how efficient they really are. To know if the windows you are considering adding to your home are truly efficient, you’ll need to know how the Department of Energy rates them in each of these categories:
- Infiltration: This term is used when referring to the amount of air leakage through and around unsealed joints in the structure of the window. Its Air Filtration Value is indicated by the cubic feet of air per minute/sq. footage of the window. The lower the air infiltration, the less air leakage.
- Conduction: The definition of conduction is the passage of heat through a solid material from molecule to molecule. With windows, heat is able to pass through the glass and the frame of the window. A window’s ability to resist this transfer of heat is referred to as it U-factor. The U-factor represents the heat flow per hour; measured in Btus per hour or watts.
- Radiation: Defined as the movement of energy through space. The two types of radiation heat transfer are longwave and shortwave radiation. Long wave is the heat transfer between objects at room or environmental temperatures. Short wave refers to the radiation from the sun. A window’s efficiency in controlling this transfer of heat from the sun is referred to in the industry as its Solar Heat Gain Coefficient.
By paying attention to the ratings of an energy-efficient window, you’ll be able to enjoy the benefits of lower energy waste, lower energy bills and higher savings over the lifetime of the windows.