Stove size calculator
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check the figures against your stove's manual, your supplier and your installer.
Short answer
Enter your room's length, width and ceiling height, and how old the house is. The calculator works out the room's volume and turns it into a heat output range in kW using rules of thumb, shown side by side with the working. Every figure is editable. Take the range to your HETAS-registered installer, who makes the final call.
Worked example
| You enter | Value |
|---|---|
| Room length | 5 m |
| Room width | 4 m |
| Ceiling height | 2.4 m |
| When was the house built? | 1930 to 2000 |
| The room is open to another space | No |
Rule of thumb: about 3.4 kW for 48.0 m³. A starting point for your installer, not a design
| Result | Value |
|---|---|
| Rule-of-thumb heat output | about 3.4 kW |
| Volume heated | 48 m³ |
| Rule of thumb | Volume ÷ | Heat output |
|---|---|---|
| Rule of thumb A | 14 | 3.4 kW |
| Rule of thumb B | – | – |
Show the working
- Room: 5 × 4 × 2.4 m = 48 m³
- Rule of thumb A: 48 m³ ÷ 14 = 3.4 kW
- Rule of thumb B: divisor not yet confirmed, so not shown
How it works
- Volume (m³) = length × width × ceiling height (plus the other space when the room is open plan)
- Rule of thumb A: kW = volume ÷ 14 (brief §4; source to be confirmed)
- Rule of thumb B: kW = volume ÷ a second divisor (not yet confirmed, so not shown)
- Each is multiplied by an insulation adjustment for the house's age once that adjustment is confirmed; until then the figures are unadjusted
These are rules of thumb, not a heat-loss calculation. A bigger stove isn't better: an oversized stove gets run turned down, burns cool and smoky, and blackens the glass and the flue. Your HETAS-registered installer will size the stove for your room, chimney and ventilation.
For a proper figure, a room-by-room heat-loss calculation counts walls, windows, insulation and air changes.
Assumptions and sources
The figures this calculator starts from, and where each comes from. Your stove's spec plate, your supplier and your own meter readings come first: change any figure to match.
This calculator has no built-in defaults: every figure comes from you or your product's data.
| Table | Clause | Nations | Status |
|---|---|---|---|
| Room-volume rules of thumb for stove size brief §4 sizing.js (Researcher to cite a published source for each rule, e.g. HETAS, a stove maker or a trade body) | Rules of thumb only, not a heat-loss calculation. Rule A is the brief's example (m³ ÷ 14). Rule B and the insulation-era adjustments are not in the brief and stay null until the Researcher cites them. | UK-wide | 1/6 values entered Not yet checked against the source |
Rules of thumb and reference figures are checked against their sources before launch; anything not yet checked is marked.
What to buy
FAQs
How do you work out what size stove you need?
Multiply the room's length, width and ceiling height to get its volume in cubic metres, then divide by a rule-of-thumb figure to get kW. House age, insulation and open-plan layouts all move the answer.
Why does the calculator give a range, not one number?
Rules of thumb disagree, and no rule knows your windows, walls or draughts. A range is more honest, and your installer narrows it down.
Should I round up to a bigger stove?
No. An oversized stove gets run turned down, which makes it burn cool and smoky. See what size stove do I need.
Does this replace an installer's survey?
No. Installing a stove is notifiable building work, and a HETAS-registered installer checks the room, hearth, chimney and ventilation before anything is fitted.
Guides
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