On Wed, 20 Oct 2010 11:36:53 -0700 (PDT), wrote:
Harry is mostly correct on this one. The rate of heat loss from a
closed system is proportional to the temperature difference.

Sorry, yes, you're right -- for conduction.

For radiation, the transfer rate is proportional to the difference
between the fourth powers of the temperatures:

http://hyperphysics.phy-astr.gsu.edu...stefan.html#c2

So with good insulation in the case under discussion, with most of the
heat interchange being conductive, the total interchange is close to
directly proportional.

However, most wall systems do involve some radiative transfer too, and
walls with no insulation will have quite significant radiative
transfer. However, I don't know just how much.

Edward