We recently had (expensive) custom windows made and installed and during an unrelated inspection the inspector mentioned that these windows need temporary stickers indicating energy values (R ratings etc) that meet minimum ratings specified in our California Title 24 reprt. Despite these windows being expensive they didn’t even come with weatherstripping! Can you believe it. Does anyone know how to go about obtaining ratings for windows after they have been installed? Is it the job of an outside agency? The window maker says he has never run into this question before. I can’t believe that no inspector has ever queried the ratings on any of his windows.
1. Is it the window makers responsibility to provide these ratings?
2. If some of the windows don’t meet the required ratings how can we work around that, for example can we add extra insulation somewhere else (like in the walls or ceilings) to compensate.
Replies
Is your custom window maker from CA?
Yes
There are no specific regulations for a window manufacturer to know the energy ratings of their windows.
If you buy windows from a major manufacturer, you will have information on energy performance, sound performance, light transmission, air and water infiltration...more.
But, to get those numbers the window company spends literally millions of dollars a year in testing and certification.
There are well over 1000 window manufacturers in North America, ranging from Andersen at number one to a couple of guys in a garage producing 27 windows a year.
Andersen's annual sales are in excess of two and a half billion dollars. By the time you get to the 100th largest window manufacturer that annual sales total has dropped to about 20 million or so...by the time you get to a good many of the smaller "custom" manufacturers, their total sales are less than a company like Andersen spends on corprate lunch...basically, these small companies cannot afford to have their windows rated...they don't have enough money to afford the certifications.
As a consumer, that leaves you in an awkward position. If you buy from one of the larger manufacturers, you have the information - if you ever need it. If you choose to support a local (and possibly very good) shop, then you may not have that information if you need it.
And finally, if the inspector wanted to know the window's "R-value" specifically, then I would suggest he may be conscientious, but he may not actually understand how windows are performance rated. Window energy ratings should be expressed in U-value numbers and not R-value...
Thanks, thats very helpful. Do you know our next step? How would we go about getting the U value to show to the inspector? Unfortunately the owners asked for and were supplied with single pane windows (to match existing) which I can't understand. So we have a dilemna, can we even get them rated & if so surely they wouldn't be up to much. Could we bring in insulation values in walls & ceilings and even such things as the 3' overhang which would provide some shade. Could the whole envelope be taken into consideration instead of just the windows. Thanks again.
R value is simply the inverse of the u value. That is, u/1=r.
I would think that there is an implied warranty of merchantability with any window made in California for use in California. That is, if a product is sold, it's implied that the product is suitable for its intended purpose. If it doesn't comply with the laws governing its intended use, then it's not merchantable and the manufacturer should make good. You need to talk to the inspector and the manufacturer more.
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Edited 2/2/2006 3:43 pm ET by Andy_Engel
While it is absolutely true that R-value and U-value numbers are inverse of one another (R = 1/U and U = 1/R), they are not really the same.
R-value is resistance to heat transfer thru an object while U-value measures heat transference thru an object...looks like a very subtle difference, but there are reasons to use one or the other in specific situations.
And, BTW, I should not have suggested that the inspector might not be knowledgeable. I deal with inspectors occasionally that are less than 100% competent and I have a certain skepticism at times...but it was still inappropriate.
Sales folks like to brag that their window has a great R-value compared with their competitor's window...but, almost always that "great R-value" is based on a center-of-glass reading which is the warmest spot on any window. A real number, but if used inappropriately, it is very misleading.
U-factor (actually more "correctly" used than U-value for windows), on the other hand, takes the entire window unit performance, not just one specific part, into consideration for the value given.
Windows pass heat at different rates at various parts of the unit. Center-of-glass is not the same as edge of glass. Heat loss thru the glass isn't the same as heat loss thru the jamb or meeting rail. R-value, by definition, cannot account for these variations. Also, R-value, again by definition, only takes into account heat transfer via conduction. Heat is transfered in three ways - conduction, radiation, and convection. As anyone who has ever stood in front of a window on a sunny day can attest, radiation is a significant part of the heat transfer thru a window.
Anyway, off topic for the original question, so back to the topic -
I agree that a window company that manufactures and sells in California should be aware of the appropriate California codes. I also believe that the window company has a responsibility to know that what they are selling meets minimum requirements...not necessarily from testing the units to NFRC specifications, but there are computer programs available that can give a very close approximation of a window's (or door, or wall system) performance values based on the materials and techniques used in the construction, the specific style or type, etc.
I also would discuss this issue (at length if necessary) with the company that made the "expensive" replacements...and ask them to calculate the energy performance numbers of their windows.
On the negative side, single pane units will have very poor performance numbers and while that can be "overcome" by adding insulation elsewhere in order to acheive an overall performance, but that is certainly not an ideal situation.
Agreed on most issues. However, I'm not certain you've got this exactly right:
U-factor (actually more "correctly" used than U-value for windows), on the other hand, takes the entire window unit performance, not just one specific part, into consideration for the value given.
It should do those things, and perhaps the NFRC regs require it now. In the past, U could be from any part of the glass. Of course, you get better performance in the center of the glass than at the edges, where the spacers conduct heat quite well compared to say, argon. Some manufacturers would not differentiate in their ads, making their products look better than they in fact were. I think the term to look for is "whole unit U-factor."Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Yep, one could use the U-value for just the glass of course, and I should have been more specific...NFRC U-value numbers are based on the entire window assembly, and knowing that number one could certainly convert it to R-value for comparison.
But, when a window salesman is preaching R-value, 99 times out of 100 that salesman is pushing a center-of-glass reading and not the overall window performance, and that is why I caution people to ask about U-values rather than R-values..
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