There is no air purge. If you have a confirmed source of fire on the flight deck and are carrying out the smoke removal checklist there is instruction to open the first officers window.....that's about the closest to an air purge I can think of.
As far as the primary source of heat goes, I imagine it is a combo of both. One checklist tells you to pull window shades and turn Galley power off so that is covering both elements you mention. I would have thought the pax themselves would be a major source of heat. The MEL for unpressurized flight limits the number of pax to 45 presumably for that reason?