What Size Wood Burner Do I Need? Room Size to kW Chart (UK)
The rule for a wood burner is to divide the volume of the room in cubic metres by 14. A living room of 5 × 4 m with a 2.4 m ceiling is 48 m³, which needs about 3.4 kW, so a 4 kW stove. A well-insulated room needs less (divide by 25), and a draughty, poorly insulated room more (divide by 10). The wood burner size calculator does it for your own room, and tells you the air vent the stove needs.
Stove size by room
The kW needed for common rooms, with a 2.4 m ceiling, for three levels of insulation:
| Room | Volume | Very well insulated (÷ 25) | Average (÷ 14) | Poorly insulated (÷ 10) |
|---|---|---|---|---|
| Small snug (3 × 3 m) | 22 m³ | 0.9 kW | 1.5 kW | 2.2 kW |
| Small living room (4 × 3.5 m) | 34 m³ | 1.3 kW | 2.4 kW | 3.4 kW |
| Living room (5 × 4 m) | 48 m³ | 1.9 kW | 3.4 kW | 4.8 kW |
| Large living room (6 × 4.5 m) | 65 m³ | 2.6 kW | 4.6 kW | 6.5 kW |
| Open-plan kitchen and living space (8 × 4 m) | 77 m³ | 3.1 kW | 5.5 kW | 7.7 kW |
| Large open-plan space (10 × 5 m) | 120 m³ | 4.8 kW | 8.6 kW | 12.0 kW |
The nearest common stove sizes are 4, 5, 6, 7, 8 and 9 kW. Choose the one just above the figure for your room. A stove in an open-plan space heats the whole connected volume, so use the volume of the whole space: an 8 × 4 m room with a 2.8 m ceiling is 89.6 m³ and needs 6.4 kW.
What changes the answer
- Insulation. The same room needs 1.9 kW when it is very well insulated and 4.8 kW when it is poorly insulated. Loft insulation, cavity wall insulation and double glazing do more for the room than a bigger stove. Use the loft insulation calculator.
- Open doorways and stairs let the heat flow into the next room, so the volume of the connected space counts.
- High ceilings and big windows raise the volume and the heat loss.
- Use. A stove that is on every evening in a living room needs a different size from one that is for the odd cold night.
Air vents and Building Regulations
A stove burns the air in the room, so Approved Document J (England) asks for a permanent air vent above a certain size of stove. The free area of the vent, for a stove in an older house and in a very airtight house (a design air permeability of 5.0 or less):
| Stove output | Older or leaky house | Very airtight house |
|---|---|---|
| 4 kW | 0 mm² | 2,200 mm² |
| 5 kW | 0 mm² | 2,750 mm² |
| 6 kW | 550 mm² | 3,300 mm² |
| 7 kW | 1,100 mm² | 3,850 mm² |
| 8 kW | 1,650 mm² | 4,400 mm² |
| 9 kW | 2,200 mm² | 4,950 mm² |
| 10 kW | 2,750 mm² | 5,500 mm² |
Other rules apply in Scotland, Wales and Northern Ireland. Ask your installer.
Before you buy a stove
- Installation. Use a HETAS-registered installer, or get building control approval. You will need a certificate when you sell.
- Flue and hearth. The chimney must be lined and swept, and the stove needs a non-combustible hearth and safe distances to walls and furniture.
- Smoke control areas. In a smoke control area you must burn authorised fuel or use a DEFRA-exempt stove.
- Fuel. Burn dry, seasoned wood (below 20% moisture) or approved smokeless fuel. Wet wood makes smoke and tar.
- Alarms. Fit a carbon monoxide alarm in the room, and a smoke alarm.
If you also want a radiator-based system, see the radiator size calculator. These sizes follow a common rule of thumb; ask a HETAS installer to confirm the output for your home.
Frequently asked questions
What size wood burner do I need for my room?
Divide the volume of the room in cubic metres by 14. A room of 5 × 4 × 2.4 m is 48 m³ and needs about 3.4 kW, so a 4 kW stove. Use 25 for a very well-insulated room and 10 for a poorly insulated one.
What size room will a 5kW wood burner heat?
About 70 m³ of an averagely insulated room, which is 29 m² of floor with a 2.4 m ceiling. A well-insulated room can be larger, and a draughty room smaller.
Does a 5kW stove need an air vent?
Not in an older house: a stove of 5 kW or less needs no permanent vent under Approved Document J (England). In a very airtight house, every stove needs a vent of 550 mm² for each kW of output, so 2,750 mm² for a 5 kW stove. Above 5 kW the vent is 550 mm² per kW above 5.
Is a bigger wood burner better?
No. A stove that is too big overheats the room, so it is run on a low, slow burn, which makes smoke and soot and blackens the glass. Choose the size for the room.
Do I need a HETAS installer for a wood burner?
A stove should be installed by a HETAS-registered installer, or with building control approval, so that the work is signed off. In a smoke control area it must be a DEFRA-exempt appliance.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.