What size stove do I need? kW by room size

By the Logcroft team · Last checked 21 October 2026

Start with the room: multiply length by width by ceiling height to get its volume in cubic metres, then divide by a rule-of-thumb figure to get a heat output in kW. It's a starting point, not an answer. The house's age, its insulation and whether the room is open plan all move the figure, and your HETAS-registered installer makes the final call.

What to look for

Stoves are sold by heat output in kilowatts (kW). Two numbers matter on the spec plate or listing:

• Nominal heat output: what the stove gives out when it's burning as designed. Size on this one.
• Maximum output: what it can manage flat out. A stove run at its maximum for hours on end isn't being run well.

The common rules of thumb divide the room's volume by a fixed figure. Our calculator shows them side by side, labelled as rules of thumb, so you can see how much they disagree.

Then adjust for the house:

• Older, draughtier houses lose heat faster, so the same room needs more output.
• Modern and new-build houses hold heat well. A stove sized by an old rule of thumb can easily be too big.
• Open-plan rooms spread the heat into the next space, so the room warms more slowly.

Why bigger isn't better

It's tempting to round up "to be safe". Don't. A stove that's too big for the room gets turned right down to stop the room overheating, and a turned-down stove burns cool. A cool fire smokes, tars the flue and blackens the glass, and you get less heat out of every log. A right-sized stove burning briskly is cleaner, warmer to sit by and cheaper to run.

If you want one stove to heat more than the room it's in, say so to your installer. That's a different job from sizing for a single room, and they may suggest a heat-loss calculation for the house.

What your installer will check

Fitting a stove is notifiable building work, so a HETAS-registered installer (or building control) signs it off. Before anything is fitted they'll look at:

• The room: its size, how well it holds heat and how it connects to the rest of the house.
• The hearth: what's needed under and around the stove you've chosen.
• The chimney: its condition, whether it needs a liner, and whether it suits the stove.
• Ventilation: whether the room needs extra air for the stove to burn properly.

Use our figure to go into that conversation with a sensible range, not to choose a stove on your own. See what a stove installer checks.

Mistakes to avoid

• Sizing on maximum output. Compare nominal outputs.
• Rounding up a size "just in case". An oversized stove burns badly.
• Forgetting the doorway. If the room is open to a hall or kitchen, count it, or ask your installer how to treat it.
• Choosing before the survey. Your installer may find the chimney or hearth limits what you can fit.

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