Article:

U and R Values for Home Replacement Windows

     There's' all kinds of information, wrong or right, about building material--including windows-- insulation thickness, quality, and various types and ratings.

     Of course, as a homeowner, I want the BEST insulation--whatever that means--to me the best means the insulation does it's job--it keeps a house warmer in winter and cooler in summer and doesn't let mold grow someplace I can't see it...

     Best also means it does the "most" insulating that's possible--it keeps the house the warmest or the coolest it's going to get.

     Well, there definitely are different types of insulation, and there are different types of insulating functions and how it's all rated for sure.

     The NFRC (National Fenestration ("window") Rating Council), a non-profit independent windows-regulating body, came up with some of the insulating functions and ways a window could be rated for its insulating qualities.

     These figures have become home building materials standards now and the standards keep changing and getting more strict.

     In fact, many windows companies DO NOT want to readily disclose their ratings because their ratings are BAD.

     Simply, insulation factors can be very complex ratios measuring various physics components that create the the meanings for "best" or "worst" or something in the middle.

     U and R values are some of those factors used to judge a window or siding for its energy efficiency--its ability to save heat in the winter and save cool in the summer. Many homeowners and sales people get these mixed up. Most homeowners are more familiar with "R" value.

     However, U-Factor is far more meaningful for a window because the U-Factor applies mostly to the GLASS and SPACER and LOW-E coating of the window assembly. Depending on the evaluator, the frame also can be calculated in the U-Factor.

     The U-Factor can also change slightly with window SIZE and WHERE in the actual window pane the measurement is taken (dead center, overall, etc). Obviously, a big picture window is going to be less energy efficient than a little bathroom window.

     The U-Factor should be LOW in any case. Cheap windows average about .35 to .41. BEST windows average about .28 to .31 or lower. Plain clear single pane glass is about 1.11.

     R-value applies to the frame. The R-value should be HIGH. R-value usually applies to the insulation in house walls. A 2x6 wall with "good" insulation has an R-value of about R-19. A good window frame R-value is about R-3 or R-4 and is rarely brought up in the window brochures because even though a 3 or 4 is really good for windows, it certainly is not insulated like a wall and sounds bad!

     Therefore, an "r-value" for example measures thermal "r"esistance( and more in the complexity of it) of a building material.

     A "u-factor" measures a "u"nit of thermal conductance.

     Fancy words and explanations--but what makes an insulation product the best?

     Again, the only rating that matters for windows is the U-Factor. R-Value is used mostly for siding insulation, though the R-Value can apply to a window frame rating and should be HIGH.

     And the lower the U-Factor= the lower your heating and cooling costs.

     Recently (2007), window manufacturers and ratings councils have been combining the U, R and other values to get a more accurate total window rating. For an excellent updated discussion on all the ratings, visit the Amerimax website at www.amerimaxwindows.com.

     Michael Dennis

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About the author

IPS Group, Inc. Board Member and Director of their Home Improvement Division, Michael Dennis is an avid real estate fix and flip investor, a former long-time replacement window salesman, and the author of several books and websites on home replacement windows including How to Save Thousands on Replacement Windows: The Homeowner's Insider Secrets Manual, and the tell-all report on the big-brand home improvement centers, The 7 Myths The Big-Brand Home Improvement Centers Want You to Believe About Replacement Windows.  Visit their website at www.vinylwindowmanufacturer.com to get your copy TODAY.

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