Our radiators heat using a combination of radiated and convected heat. Radiation works by heating the people in the room directly; as the surface of the radiator heats up, it pushes out heat into the room. Radiated heat is effective no matter what the size of the room – however, radiated heat only makes up about two thirds of the radiator’s heat output.
Convected heat, meanwhile, works by filling rooms with warm air. As cool air circulates around the room it is warmed by the hot elements inside the radiator. Because hot air rises, the warmer air will rise to the ceiling, allowing the remaining cooler air to circulate through the radiator and warm up in turn. The problem with heating by convection is that the warmed air can easily be lost through draughts and opened doors. The poorer your insulation, the faster your room will lose heat and the more powerful your radiators will need to be to keep the warm air topped up. In larger rooms and rooms with high ceilings you are effectively trying to heat a larger volume of air than in standard sized rooms, so you will need more powerful radiators to keep the entire space filled with warm air.