Radiator size for a 5 × 5 m room, by type of room
A 5 × 5 m room is a large living room or a kitchen-diner. The floor area is 25 m² and, with a 2.4 m ceiling, the volume is 60.0 m³. These figures assume double glazing, one external wall and filled cavity walls. The last column is the ΔT50 rating to look for if a heat pump supplies the radiators.
| Room | Heat needed | BTU | Rating for a heat pump (ΔT50) |
|---|---|---|---|
| Living room (21°C) | 3,300 W | 11,260 BTU/h | 6,411 W |
| Bedroom (18°C) | 2,888 W | 9,852 BTU/h | 5,610 W |
| Kitchen (18°C) | 2,888 W | 9,852 BTU/h | 5,610 W |
| Hall or landing (16°C) | 2,613 W | 8,914 BTU/h | 5,075 W |
External walls and insulation
Every outside wall loses heat, and solid walls lose more than insulated ones. Living room at 21°C, double glazing, 2.4 m ceiling.
| External walls | Solid walls, not insulated | Cavity walls, filled | Well insulated |
|---|---|---|---|
| None (an inside room) | 3,366 W | 2,805 W | 2,384 W |
| One | 3,960 W | 3,300 W | 2,805 W |
| Two (a corner room) | 4,554 W | 3,795 W | 3,226 W |
| Three or more | 4,950 W | 4,125 W | 3,506 W |
Taller ceilings
A taller room holds more air to heat. Living room, double glazing, one external wall.
| Ceiling height | Room volume | Heat needed | BTU |
|---|---|---|---|
| 2.4 m | 60.0 m³ | 3,300 W | 11,260 BTU/h |
| 2.7 m | 67.5 m³ | 3,713 W | 12,667 BTU/h |
| 3.0 m | 75.0 m³ | 4,125 W | 14,075 BTU/h |
One radiator or two?
At 3,300 W, a room this size is often better with two radiators, one under each window or on facing walls, which spreads the heat and keeps each radiator a sensible size. Add up the ΔT50 outputs printed on the radiators so the total meets the figure.
These are quick estimates from the room volume. For a heat pump, or a room with large windows, ask an installer for a room-by-room heat loss calculation. The radiator size guide explains ΔT ratings, and the boiler size calculator sizes the whole system.
Want to change anything else? The calculator above is the full Radiator Size Calculator (UK, Watts and BTU): edit any number and the results update instantly.
Tools & materials for this project
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Frequently asked questions
What size radiator do I need for a 5 × 5 m room?
About 3,300 W (11,260 BTU/h) for a living room with double glazing, one external wall, cavity wall insulation and a 2.4 m ceiling. The same room as a bedroom, heated to 18°C, needs 2,888 W.
How many BTU to heat a 5 × 5 m room?
11,260 BTU/h for a living room, or 9,852 BTU/h for a bedroom. A cold corner room with solid walls and single glazing needs 18,646 BTU/h.
What radiator size for a 5 × 5 m room with a heat pump?
A heat pump runs at a lower flow temperature, so the radiators give less heat. Choose a radiator rated about 6,411 W at ΔT50 for a living room this size (it gives about 3,300 W at ΔT30), or 5,610 W for a bedroom.
Related sizes and guides
Related sizes
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.