On Thu, 19 Apr 2007 10:36:09 +0100 The Natural Philosopher wrote :
And the airgap? Now add that.. If the unit is sealed reasonably well, a
4-6" airgap is going to be a LOT better than a double glazed unit.

No, because once the gap gets beyond a certain figure (around 16-20mm)
convection currents within the gap cancel out the effect of the extra
space.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk