What Does U-Factor and R-Value Mean in Replacement Windows?

replacement window u factorOnce you’ve started the process of looking into purchasing a new set of replacement windows for your home, it won’t be too long before you come across some terms that may not be familiar to you. It’s likely that one of those foreign terms will be a numerical rating known simply as the U-Factor, so in today’s post from Renewal by Andersen of Central New Jersey, that’s going to be our main focus. However, we’ll also take some time to discuss the other ratings systems that occasionally come into play when shopping for replacement windows.

Replacement Window U-Factor vs. Insulation R-Value

Not to be confused with R-Value, which you may have come across if you’ve ever had occasion to deal with home insulation, the U-Factor system for windows was put in place by the National Fenestration Rating Council (NFRC) as a means to measure the amount of heat that is lost through a window. R-Value is essentially the U-Factor’s evil twin— similar but opposite. You want a lower U-Factor rating, as that signifies less heat lost through your windows, as opposed to a higher R-Value rating, as that signifies more heat resisted by the insulation.

How to Use the Replacement Window U-Factor

For you as a buyer, the U-Factor rating is a tool of paramount importance that will make a big difference in your happiness with your windows later down the road. The U-Factor rating allows you to find out, before you purchase your windows, which ones will be the most energy efficient — saving you money on your utility bills and keeping your home at a comfortable temperature. The U-Factor rating scale is from .10 (least heat loss) to 1.20 (most heat loss). Remember, the lower the rating, the more efficient the window.

Other Rating Systems

The U-Factor is not alone on the list of rating systems developed by the NFRC. Two of the more common ones are the Solar Heat Gain Coefficient (which measures how much outside heat a window prevents) and the Visible Transmittance (which measures how much light comes through a window). Both are measured on a 0 to 1 scale. A superior window will have a low Solar Heat Gain Coefficient and a high Visible Transmittance rating.

Still noteworthy, though less commonly known, are Air Leakage and Condensation resistance factors. Air Leakage, measured from .1 to .3 will tell you how much outside air will leak through your window, so a lower number is preferable. Condensation Resistance, unsurprisingly, lets you know how well your window will resist condensation. Condensation Resistance is measured from 1 to 100, and unlike Air Leakage, you’ll be looking for a higher rating.

Contact Renewal by Andersen of New Jersey for More Information

Need any more information about U-Factor or other window ratings? Renewal by Andersen of Central New Jersey can help. As a subsidiary of Andersen Windows, we are your one-stop shop for all of your replacement window needs. Contact one of our experienced design consultants with any questions you may have. Call us today at 1-888-826-2451 or fill out the short form on this page for a free design consultation.

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