What you should know about energy safe.
U-FACTOR / U-VALUE
U-factor, sometimes called U-value, is a measurement of a product’s resistance to heat loss. Windows with a lower U-factor provide better insulation, meaning they don’t let as much heat escape as windows with a higher U-factor. Choosing windows with a low U-factor, since you won’t have to compensate for heat loss by running your heating system as high or as often.
SOLAR HEAT GAIN COEFFICIENT (SHGC)
Solar heat gain coefficient (SHGC) refers to the amount of solar radiation transmitted through a window and into a home or building. SHGC will appear as a number between 0 and 1, with a lower number indicating that the window transmits less solar heat.
Low-E glass typically reduces solar heat gain with its protective coating, which can help control air conditioning use during the summer.
VISIBLE TRANSMITTANCE (VT)
Expressed as a percentage, visible transmittance refers to the amount of visible light allowed to pass through a window. A lower number means less light will enter the home or building. This is typically the result with Low-E glass windows, which use a special coating to reduce solar heat gain.
Air leakage is a measurement of the amount of air that passes through cracks in a window. A higher rate of air leakage indicates the window is more susceptible to heat loss and gain, which reduces energy efficiency and interior comfort.
ENERGY RATING (ER)
This figure captures the overall energy-efficiency score of a window. It encompasses all factors for a more convenient way to compare products. The standards for energy ratings vary, a window must have a minimum energy rating of 25 in zone 1, 29 in zone 2 and 34 in zone 3.