Heat is transferred by conduction and convection (in this case). Perhaps
argon is better on both counts, but it would be nice if the whole mechanism
was translated into R values, so you'd know what it costs for an additional
R unit.

Rich


Rich, the "whole mechanism" *is* translated into R values. The U factor (and
other data) is marked on a sticker placed on every window sold today. U factor
is the inverse of R value. If you buy a plain window where U = .55, that is an
R value of 1/.55 = 1.8. A good LowE, argon filled window is about U = .32, so
the R value is 3.125. Those stated values are for the entire window assembly
tested as a unit, so it already includes convection effects of the fill gas, as
well as conduction of the gases, frames, air leakage, etc.

Occasionally you used to see a manufacturer trying to sneak by with an
advertised "CoG" U factor. That means Center of Glass, and the U factor will be
deceptively good, since it does not include the heat losses through the frames.
I haven't seen a CoG claim in awhile, however, and at any rate, that is not the
value that must be printed on the sticker.

Dennis