It is to me, criminal that the advertisers of such products are allowed to
get away with their claims for the plug-in socket sized heaters. A
kilowatt heater running for 1 hour is not going to produce more than a
kilowatt hour of heat on its’ own (unlike a heat pump which extracts heat
by using electricity to run a compressor enabling it to extract heat from
the air and use this to heat a space which may well allow the pump to
produce 3 kilowatts of heat for every kilowatt of electricity consumed to
power the system.
Those small electric heaters usually have a ceramic mass in them which the
electrical element heats up - and it is then blown out of the front grill.
One might argue that not all the energy is given off as heat anyway so they
are probably less efficient than a conventional convector or oil-filled
radiator type heater. I can’t recall the power rating of these devices but
if for arguments sake, I say they are 500 watt/h, it will certainly not
warm up anything much larger than a rabbit hutch in minutes as they seem to
claim!