The answer depends on whether it is a wet (part of central heating) or dry (pure electric) heater.
My plumber is about to supply a wet Myson Kickspace. These have a small fan which draws in cold air and pushesz out warm air. It is low powered as it is not doing the heating, just blowing air across the heater space. This will be fitted with a 3-pin plug (3 Amp fuse - so there's the clue about consumption requirements) into an unswitched socket (isolated by Grid Switch).
The power requirement will be totally different for an all electric heater of course.
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