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U-Factor and R-Value Ratings

The best ways to measure the effect of windows on energy use are known as the U-factor and R-Value ratings.

U-factor = measures the rate of heat transfer (or loss) – the lower the number the better

R-Value = measures the resistance to heat loss – the higher the number the better

According to the National Federation Rating Council, one of the best ways to measure the effect of windows on building energy use is to look at the U-factor rating. This is because windows interact with the environment and are acceptable to changes in outside temperatures, wind, and sunlight. The R-factor while it is a great measurement of resistance only accounts for the conductivity while the U-factor takes into all the factors in to account including the type of glass. Therefore the U-factor explains the energy loss for the entire window unit.

Important to remember is the lower the U-factor the great energy efficiency and the higher the R-Value the greater the energy efficiency!

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