The message from Andy Wade contains these words:
I may be venturing into the unknown (or at least somewhere I haven't been for the best part of 40 years) but the difference between say 290 K and 287.6 K is just about significant at the 4th power but it pales into insignificance when the temperature difference is say 15 K.
No. The warm body in question is the human body that dIMM maintains loses heat very much faster when the ambient temperature is raised to compensate for the discomfort caused by having a poorly insulated house.
Well for a start a poorly heated room needs much more heat to keep it up to temperature than a well insulated room and if that heat is supplied by a radiator some 40% is probably radient heat. If supplied by a fire it will of course be a much higher percentage.
Secondly the radiator (if that is the heat source) being considerably hotter is a much better radiator than the cool walls. If the walls are say at 16 C, the warm body at 39 C and the radiator at say 60 C I will leave you to work out what those proportions would mean in degrees K at the 4th power.