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Window Spacer Performance: How does Window Spacing affect U-Value?

Source Post:

I was researching the internet this morning, hoping to find a graphic presentation of spacer performance. Unfortunately, I couldn't find one anywhere. Oh well.

Thanks for the clarification FenEx about IGU width and airspace width -- I hope that I wasn't confusing when I was discussing gap spacing versus overall IGU spacing.

Anyway, one really interesting fact about using inert gasses and Low-E coatings in an IGU is the performance of the gasses at various "thicknesses" of the airspace(s) within the IGU....which I think was something of the original question.

The current very best, most energy efficient, spacing/gas combination is Xenon in a triple glazed IGU with "airspaces" of about 7/32" each....we are looking at a U value of .09 in that construction.

There was a question posted a few days ago about whether or not triple glazing is an advantage over double glazing. A triple glazed unit with Krypton fill and Low-E on two different surfaces cannot quite match the performance of Xenon fill, but it is available and it is pretty darn hard to beat....U values of .10 are achievable. Dual-pane Argon will theoretically peak at about .13...none of which are particularly bad numbers, but remember that these are also optimum numbers that depend on other factors as well.

At the "thin" space-widths, Argon isn't nearly as effective as the other gasees but by the time you approach a 7/16" width airspace the advantages of Xenon and Krypton are a bit less.

Xenon fill peaks at about 7/32" and begins to decline in perfomance almost immediately, and Krypton peaks at about 5/16" and is pretty consistent up to about 1/2" where its performance begins to decline, but that is also where Argon peaks - but even there Argon does not "quite" match Krypton performance.

Also, when I say perfomance declines, I am not saying that suddenly it doesn't work fact, both of those gasses continue to work very well... just that they are past their peak performance area.

Typical Argon performance peaks at about 7/16" to 9/16"...but even at its peak performance, Argon cannot quite match either Xenon or Krypton even when those two gasses are no longer performaing at their optimum.

Hope this makes some sense?

Source Post: What difference, if any, does Gap Width make?

Posted: Thu Oct 14, 2004 10:10 am