BTU (British Thermal Units) measures the heat output a radiator needs to warm a room. This estimates it from the room volume and type, since living rooms and bathrooms are usually kept warmer than bedrooms. It is a starting point: for an accurate specification, a proper heat-loss calculation also factors in insulation, windows, external walls and floor type.
Heat your home
Stay cosy.
Radiator thermostatic valves
Control each room.
Radiator reflector foil
Keep heat in the room.
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Frequently asked questions
What happens if a radiator is too small?
It will struggle to reach a comfortable temperature on cold days and run constantly. It is usually better to size up slightly, especially in poorly insulated rooms.
Is this a full heat-loss survey?
No — it is a quick estimate from room size and type. For new heating systems, use a detailed heat-loss calculation that accounts for insulation, glazing and external walls.