Fireplace Size Calculator
Enter the room's length, width and ceiling height, and how well it is insulated. The calculator gives the stove output in kW, the size of an open fireplace opening, the flue size and how far the hearth must reach.
- Stove kW
- Fireplace opening
- Flue and hearth
Use the room the fire is in. Open plan spaces count as one room.
A stove should match the room, not the biggest model you can buy. A common rule is the room volume in cubic metres divided by 14 for an average room. A 5 × 4 m room with a 2.4 m ceiling needs about 3.4 kW. An oversized stove is run slowly, which soots the glass and chimney.
Stove size chart
2.4 m ceiling, average insulation. Search for a room.
| Room (m) | Volume (m³) | Stove (kW) | Well insulated (kW) |
|---|---|---|---|
| 3 × 3 | 21.6 | 1.5 | 0.9 |
| 4 × 3 | 28.8 | 2.1 | 1.2 |
| 4 × 4 | 38.4 | 2.7 | 1.5 |
| 5 × 4 | 48 | 3.4 | 1.9 |
| 6 × 4 | 57.6 | 4.1 | 2.3 |
| 6 × 5 | 72 | 5.1 | 2.9 |
| 8 × 5 | 96 | 6.9 | 3.8 |
Use a smaller stove in a well insulated home.
Room size and stove
2.4 m ceiling. Slide the floor area.
The drawing shows an open fireplace opening sized for the room, with its stove output alongside.
How to size a stove
Volume first. Step through it.
Room volume
L × W × H.
For an open fireplace, the opening is about one fiftieth of the floor area, and the flue at least a tenth of the opening.
Wood stove, multi-fuel or open fire
Fire types. Compare them.
Closed, efficient.
Wood or smokeless fuel.
Traditional fireplace.
An open fire sends most of its heat up the chimney. A stove gives three to four times more heat to the room from the same wood.
Before installing
Fire checks. Tick each item.
Tick each item as you go.
Fit a carbon monoxide alarm in any room with a solid fuel fire.
What you get
Fireplace sizing. Each tile explains one result.
For the room.
Of the room.
Open fire size.
Minimum size.
Front and sides.
In the UK, stoves over 5 kW usually need a permanent air vent in the room.
Frequently Asked Questions
No question matches that search.
What size wood stove do I need?
Divide the room volume in cubic metres by 14 for an average room. A 50 m³ room needs about 3.5 kW.
Can a stove be too big for a room?
Yes. It overheats the room or has to be run slowly, which wastes wood and soots up the chimney.
How big should a fireplace opening be?
About a fiftieth of the room's floor area, with the height about two thirds of the width.
What size flue does a fireplace need?
At least a tenth of the opening area for a round liner.
How far should a hearth extend?
At least 16 inches in front and 8 inches each side, more for large openings.
Do I need an air vent for a stove?
In the UK, usually for stoves over 5 kW. A smaller stove may also need one in a very airtight home.
How many kW to heat a room?
About 1 kW for every 14 m³ in an average room.
A fire matched to the room
Size the stove from the room's volume and insulation, then check the flue and hearth. The fire will burn cleanly and keep the room warm without overheating.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.