I am sure I am not the first person who has wondered where to put radiators and why on earth they always seem to be put under windows?! It seems like such an idiotic place to put them, for a start the heat from the radiator escapes to the outside, or is cooled by drafts and this is only made worse in the evening if the curtains are drawn, just when you need that valuable heat the most!
One of the biggest misunderstandings about radiators is that they actually radiate very little of the heat that they emit, on average a central heating radiator will radiate about 20% of the heat and the remaining 80% is convected via a plume of warm air emitted from the top of the radiator. Sadly, this means that all of this heat is then convected up to the ceiling and in many homes the temperature difference between sofa height and the ceiling can be over 2oC, ie the ceiling is 2oC warmer than you sitting on your sofa.
And remember, you are paying for that heat!
So why place the radiators under windows? Put simply, the cool air coming from the window falls on to the rising warm air from the radiator and pushes the warm air out into the room.
The problem nowadays is that since most houses have had their windows replaced with double glazing, there is no longer that same cool air coming from the window to help mix up the heat in the room and therefore the heat from your radiator is convected straight up to the ceiling, where it stays.
So while double glazing is definitely a good thing, perhaps it’s time we moved our radiators...or you could just buy a Radfan ;)