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In uk.d-i-y, David wrote:

the pot is in a hole in the insualtion but the top is not covered with
insulation.

Then you'll get radiation losses from the top of the pot, but not much
in the way of convection, since there's not much chance of air getting
to the bottom of the pot to start an updraught. An old lath-n-plaster
ceiling will provide more in the way of airgaps for convection than a
nice new plasterboarded one - to get convection going there you'd want
to stand the pot on some spacers, or nibble some gaps into the rim (as
if the little bleeders won't crack if you try ;-)

Stefek

Exactly, as long as you have some exposed surfaces you will have losses.

I'm not too sure about your radiative/convective loss assessment though.

Given that the top of the pot is pretty much sealed it doesn't matter if you
get any air down at the bottom of the pot, by whatever means

As the loft space is going to be considerably colder than the pot, (it is
well insulated after all), and there should be decnt ventilation, then there
will be a reasonable air flow above the pot. So most of the heat may well
be removed from the top of the pot by convection.

cheers

David