- 7,200BTU for a 4 × 4m lounge
- 3.41BTU per watt
- ΔT50normal gas boiler rating
- ×2radiator size on a heat pump
Radiator size by room
Average insulation, 2.4m ceilings, gas boiler (ΔT50). Radiator sizes are 600mm high.
| Room | Size | External walls | Heat needed | Type 22 radiator |
|---|---|---|---|---|
| Bathroom (22°C) | 2.5 × 2 m | 1 | 2,293 BTU (672 W) | 600 × 400mm |
| Bedroom (18°C) | 3 × 3 m | 1 | 2,948 BTU (864 W) | 600 × 500mm |
| Kitchen (18°C) | 4 × 3 m | 1 | 3,931 BTU (1,152 W) | 600 × 700mm |
| Bedroom (18°C) | 4 × 3.5 m | 2 | 5,044 BTU (1,478 W) | 600 × 800mm |
| Living room (21°C) | 4 × 4 m | 2 | 7,206 BTU (2,112 W) | 600 × 1200mm |
| Living room (21°C) | 5 × 4 m | 2 | 9,008 BTU (2,640 W) | 600 × 1600mm |
Solid walls, single glazing, a north-facing room or big patio doors all push the figure up. A well-insulated modern house needs about 20% less.
The radiator BTU calculator adjusts for all of these, and for low-temperature boilers and heat pumps, and suggests Type 11, 21 and 22 sizes.
