I know this mod is no longer maintained but i did some tests at very cold temperatures, like -150C. And i think i understand what matters for maximum heating.

_More vents more heat.
_Flow should always be at 100% because if not vent don't heat as much.
_Thermal efficiency does not matter, at least as low as 10% ish, if lower than that heating slightly suffers.

Also Thermal efficiency does not seem to affect the speed of heating, hell, more of it possibly hiders it by a few degrees.

If anyone has any insights or wants to correct me please do so, they weren't very extensive tests but, i would like to know what's going on lol.