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 Post subject: double low-e
PostPosted: Wed Feb 08, 2006 7:43 pm 

Joined: Wed Feb 08, 2006 7:37 pm
Posts: 1
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a question...

I am presently in the midst of getting quotes for windows. One company is offering, at no extra charge, a double low-e coating on a double-paned window as opposed to the usual, one. (i assume one coating on each pane)

does another low-e coating make any real difference, or are we just splitting hairs here?

unfortunately, this company has no test results for a Canadian ER rating so it is hard for me to do an apples-to-apples comparison.


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 Post subject: double low-e
PostPosted: Wed Feb 08, 2006 11:01 pm 

Joined: Wed Feb 08, 2006 10:46 pm
Posts: 2
Location: N. Virginia
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Double low-e is slightly better than than singular. Example:

the u-value at Center-of-Glass (COG) for a regular double-paned window with an aluminum spacer is about 0.5.
the u-value at COG for standard low-e glass with argon and an aluminum spacer is about 0.33
the u-value at COG for double low-e glass with argon and an aluminum spacer is about 0.25

Remember, the lower the u-value the better the insulating value

Also, you can approximate a window's r-value by dividing 1 by the u-value

thus, the last example above would have an r-value of 4, as oppossed to 3 or 2, respectively.

This data is based on the vinyl windows I deal with on a daily basis at work.


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 Post subject:
PostPosted: Thu Feb 09, 2006 8:33 am 

Joined: Tue Dec 13, 2005 8:57 pm
Posts: 113
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Depends on what they mean by a "double LowE coating". If they mean a LowE2 (squared) versus a standard LowE, then yes, there is a significant improvement.

If they mean placing the lowE coating on both lites and not just one, then that is something of a gimmick and it isn't worth the trouble.

I have seen a good many cases where the salesfolks simply don't understand the mechanics of the LowE coating and they think that a "dual" LowE means placing the coating on two lites of glass when in reality they are looking at a LowE2 coating on one lite. Or, they think that a LowE2 means coating one pane twice - also not correct.

Canadian ER rating also includes solar heat gain in the calculations. A standard LowE coating has a good bit of direct solar gain. A LowE2 has virtually no solar gain. This difference can get technical, but for the moment I would (if I were you) clarify exactly what the window company means by their "double LowE" before going further with them.


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