A cast-iron radiator works by pushing hot water or steam through the pipes or fins, heating the surrounding air. Because warmer air is less dense, it rises away from the radiator. The colder air in the room then moves into the radiator, and the process begins again.
The main heat transfer process in a radiator is called convection. The convection process, the rising of the warmer air and the sinking of cooler air, creates currents that move out into the room to spread the heat. The movement prevents the need for electric blowers. Contrary to the product's name, radiation plays only a small role in heating a room. Radiation cannot happen effectively if the radiator is covered in a layer of dust or debris, so it is crucial to clean the external surfaces regularly.
When radiators are working smoothly, they can heat a room efficiently. Because cast-iron radiators are commonly found in homes built before the 1950s, however, they are prone to age-related problems, including rusting, sloping pipes and sagging floor boards. Excessive air buildup prevents effective circulation of steam or water through the pipes. For the convection heating process to work at optimal levels, the radiator must not be blocked by furniture, curtains or enclosures.