underfloor heating in bathroom = smaller btu radiator?

suered

Dear all - that's about it in a nutshell. Have decided to go with underfloor heating as don't want cold tootsies in winter.

Given that I was looking at a roughly 2500BTU combined towel rail/rad without the underfloor heating, can I knock off any BTUs from the requirement with it? I realise that much of the answer will depend on how much I intend using the underfloor stuff, but if anyone has a rule of thumb they could offer up, would be most grateful.

The floor currently has exotherm (I think that's the name) insulation board (the thinner one) then chipboard on top and will be tiled.

There seems to be a much wider range of combined rails/rads (trying to save on wall space, hence the combination) to choose from if you don't have to have such a high BTU (room is roughly 3m x 3m with large single glazed sash window with horrible secondary glazing). Even dropping down to 2000 would open up the choice, but I don't want to do that and then find that you're always chilly.

Thanks