How we size stoves
Our stove size calculator gives a heat output range from the room's size, using rules of thumb. This page explains what those rules are, what they leave out, and why your installer's figure always comes first.
What we do
- Work out the volume. Length × width × ceiling height, plus the next space if the room is open plan.
- Apply each rule of thumb. Each rule divides the volume by a fixed figure to give kW. We show every confirmed rule side by side, so you can see the spread.
- Adjust for the house's age once we have a sourced adjustment for it. Until then we say the figures are unadjusted.
- Show the working, so you can check the sum yourself.
What rules of thumb leave out
A rule of thumb treats every cubic metre the same. Real rooms differ: windows, outside walls, insulation, draughts, how the room opens onto the rest of the house. A heat-loss calculation counts all of that, and an installer can do one. Our figure is a starting point for that conversation, not a design.
Where our figures come from
- Rule A, volume ÷ 14: a widely quoted rule of thumb, given in our build brief.
- Rule B and the insulation adjustments: not yet sourced, so not shown.
Every figure, its source and whether it has been checked yet is listed on the calculator page and on how we calculate.
Why we never recommend a size
Installing a stove is notifiable building work, and the right size depends on the room, the hearth, the chimney and the ventilation. Only a HETAS-registered installer (or building control) can sign that off. We help you go into that conversation knowing the numbers.