Tony Bryer wrote:
On 17 Jan 2007 15:54:34 GMT Ian Stirling wrote :
You can't simply multiply the thermal resistance of a 50mm cavity by
three to get the value for 150mm, otherwise the middle of a room
would be warmest.

For a standard double glazed window the U-values in SAP2005 a
6mm gap: 3.1; 12mm gap: 2.8; 16mm or more 2.7

My understanding has always been that beyond this you get next to no
improvement since the extra space allows for convection currents up
the warmer face and down the colder one.

My guess is that the biggest effect of curtains is to kill the heat
loss from radiation.

I don't think so.

I have been watching the digital stat this winter..a sunny clear day as
opposed to a dull one nets only about 1-2C rise in the room. And thats
from the solar systems best 'radiator'

I guess the reason why we put on anoraks is to stop our bodies losing
heat by radiation eh?

multi layer things like coats and jackets that trap air in spaces are
known to be better than one thick layer..curtains when lined are simply
an example of the same.

When hanging naturally our curtains are about 1cm thick. I can't begin
to consider that is worse than a 12mm gap between two pieces of glass.

Incidentally, my figure of 14C average annual temperature is
optimistic..here's the reality.

http://www.metoffice.gov.uk/climate/...00/mapped.html

But it only makes insulation even more important.