It wouldn’t be very effective:
You have to keep the temperature of the radiator above the dew point else you will get condensation which will collect in a puddle on the floor ruining your fancy solid wood flooring. So at 21 degrees and 50% RH that is 10 degrees.
With a temperature difference (Delta t[/url]) between the radiator and the room of 11 degrees the radiator will only absorb 10% of it’s rated heat output. And thats ignoring the fact that it should be mounted at the top of the wall else you will end up with cool feet and a warm head as the cold air falls.
So a radiator that keeps the inside 25 degrees warmer than the outside would be only be able to drop the room temperature a few degrees. And you still have to get dump the heat somewhere.
TL;DR Won’t work because physics