Fireplace/Stove Calculator
Size a wood, gas or pellet stove to the room it must heat.
About Fireplace/Stove Calculator
Stove output is matched to room volume rather than floor area, since ceiling height changes the heated volume substantially. Input rating exceeds output by the efficiency shortfall, and fuel consumption follows from the input. An oversized stove is run throttled down, which produces incomplete combustion, creosote and glass staining, so matching output to the room matters more than buying headroom.
Formula
Fireplace/Stove
Output = volume × specific loss × ΔT; input = output ÷ efficiency
- specific loss
- Watts per cubic metre per kelvin, set by insulation quality
- wood energy
- Around 4.2 kWh per kilogram of seasoned hardwood
Worked example
With the default values below, Fireplace/Stove Calculator returns Heat Output Required of 2.520. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Room areaminimum 0.1 m2
- 35 m2
- Ceiling heightminimum 1.5 m
- 2.4 m
- Insulation qualityone of Poor, Average, Good
- Average
- Appliance efficiencyaccepts 20–100 %
- 75 %
- Design temperature differenceminimum 1 C
- 20 C
Results
- Heat Output Required
- 2.520 kW
- Room Volume
- 84.00 m3
- Heat Output Required
- 8,599 BTU/h
- Appliance Input Rating
- 3.360 kW
- Wood Consumption at Full Output
- 0.800 kg/h
Step by step
- 1Values used
- 2Fireplace/Stove
- 3Heat Output Required= 2.520 kW
- 4Room Volume= 84.00 m3
- 5Heat Output Required= 8,599 BTU/h
- 6Appliance Input Rating= 3.360 kW
- 7Wood Consumption at Full Output= 0.800 kg/h
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Fireplace/Stove calculated?
Output = volume × specific loss × ΔT; input = output ÷ efficiency Stove output is matched to room volume rather than floor area, since ceiling height changes the heated volume substantially. Input rating exceeds output by the efficiency shortfall, and fuel consumption follows from the input.
Why does Fireplace/Stove matter?
An oversized stove is run throttled down, which produces incomplete combustion, creosote and glass staining, so matching output to the room matters more than buying headroom.
What values do I need to enter?
This calculator takes 5 inputs: Room area, Ceiling height, Insulation quality, Appliance efficiency, Design temperature difference. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.