U-factor is an energy performance rating that measures how well fenestration products trap heat. If you’re serious about increasing thermal insulation (which you should be), it’s an important thing to check before making a purchase.
Today, Renewal by Andersen® of San Francisco talks about everything you need to know about U-factor to buy the right windows:
It Is Not the Same as R-Value
Speaking of insulation, you may have heard of R-value, which is often used when measuring the ability of the product to resist heat transfer. It’s not the same as U-factor, and their differences can be complicated.
In simple terms, what sets U-factor apart is that it aims to determine the rate of thermal transmittance. When the R-value goes up, the U-factor goes down. Expressed in a range between 0.20 and 1.20, the lower the number, the better.
Location Dictates the Maximum
ENERGY STAR® has set unique U-factor maximums in place across America to help separate extremely efficient and less promising products. In California, your zip code (instead of county) determines the climate zone to which your home belongs. For instance, the ideal U-factor value in the North-Central Climate Zone is 0.30 (or less). Any window having a rating higher than that wouldn’t receive the ENERGY STAR seal.
Furthermore, the U-factor of the product should match the recommended Solar Heat Gain Coefficient (SHGC) value in the climate zone. SHGC is also an energy performance rating, which measures the amount of sun’s heat that can pass through the unit. Based on the previous example, a product with a 0.30 U-factor (or less) must also have a 0.40 SHGC value (or less). An incorrect combination wouldn’t generate excellent results.
Other Ratings Matter as Well
U-factor and SHGC are the two most relevant energy performance ratings, but don’t forget about Visible Transmittance (VT) and Air Leakage (AL). The former measures how the product fares in daylighting, while the latter demonstrates its ability to keep unwanted drafts at bay. Anywhere you live, you should always choose windows with a high VT (ranging from 0 to 1) and a low AL (ranging from 0.1 to 0.3).
Turn to Renewal by Andersen of San Francisco to buy ENERGY STAR-certified products with exceptional energy performance ratings. Call us at (866) 609-5033 now to schedule your no-obligation consultation, learn more about our windows and receive a free estimate. We serve San Francisco and other neighboring communities.
