In article ,
Jon Rouse wrote:
In article , Nick Maclaren
writes

The glass is 1/2" cavity K glass. Definitely worth it. Condensation
is minimal and little heating is needed. It won't save money, but you
shouldn't lose money over its lifetime.

I'm curious about this one. When double glazing first came out, I was
told that the thinner the gap the better the thermal insulation, as
convection would not be so rapid in a narrower gap. A wider gap was
required for noise insulation, ideally with a tapering section so there
were no resonances. Now DG firms seem to be plugging wide gaps. Is this
because profit margins are higher on chunkier frames, or have the laws
of physics changed in the last twenty years?

No, but they never did lead to the conclusion that you were told
originally! There is a conduction effect as well, and therefore
there will be a point below which the insulation is proportional
to the gap thickness.

Looking at the figures, there is little gain above 1/2", and the
way to get better insulation is to go for triple glazing. Rarely
worth it in the UK. My guess is that the convection effect is what
stops wider gaps from being better, and my summary is that the near
optimum is 1/2".


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:
Tel.: +44 1223 334761 Fax: +44 1223 334679