We have a constant circulation hot water system. The tank doesn't feature much and feels relatively cool. The cupboard, and in fact the small room it's in, was designed for drying. The hot water and the radiator pipes to the rest of the house all run through the cupboard unlagged, so I suppose it's no surprise it's - wait for it - 36degC! (In the middle of the house so heat doesn't go to waste). OH has banned propagators from the room itself which would be ideal - not enough space she says, and I expect the seeds are ruined but just in case have moved them to GH heated propagator where there's room because the first chillies have now come out.