A radiator is a heat-emitting device, typically a metal panel or series of connected sections, through which hot water or steam circulates to transfer heat into a room via radiation and convection. Despite its name, a modern radiator actually delivers most of its heat output through convection rather than radiation.
Applications
Radiators are the most common type of heat emitter in central heating systems across Europe and much of the world. They are connected to a central heating boiler or heat pump via a network of pipes. Hot water from the boiler flows through the radiator, which heats up and transfers thermal energy to the surrounding room. Cooled water then returns to the boiler to be reheated, completing the circuit.
Several types of radiators are in common use. Panel radiators, consisting of one, two, or three pressed steel panels with optional convector fins, are the standard in most modern installations. They are lightweight, relatively inexpensive, and available in a wide range of sizes. Column radiators, with their characteristic vertical or horizontal tubes, are a traditional design that remains popular for aesthetic reasons, particularly in period properties. Towel radiators, designed for bathrooms, double as heated towel rails.
Cast iron radiators were the original standard from the 19th century through much of the 20th century. While heavy and slow to respond to temperature changes, they retain heat for longer periods and are valued in restoration projects for their historical character.
The heat output of a radiator depends on its size, surface area, water temperature, and the temperature difference between the radiator and the room. Radiators are sized based on a room’s calculated heat loss, taking into account factors such as wall insulation, window area, room volume, and desired indoor temperature.
Thermostatic radiator valves (TRVs) allow individual control of each radiator, enabling room-by-room temperature regulation and improving energy efficiency. Proper balancing of the heating system ensures that all radiators receive adequate flow and heat the building evenly.
Related terms
- Central heating boiler
- Convector
- Underfloor heating
- Thermostatic radiator valve
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