Firewood Calculator

Heated area, m²

Ceiling height, m

Climate

Species

Stove or boiler efficiency, %

Season length, months

Price per stacked m³

Result

Firewood needed, stacked m³12.13
Per month, stacked m³1.73
Heat over the season, kWh16,128
Design output, kW8
Cost of the firewoodenter the price per cubic metre
Speciesbirch

From kilowatts to a woodpile

Works out how many stacked cubic metres of firewood a heating season needs, from the floor area, the climate, the species and the efficiency of the stove or boiler.

Firewood is sold by the stacked cubic metre — a cubic metre of stacked logs including the air between them. Solid timber comes to roughly a third less than that, and it is precisely on this difference that buyer and seller usually fall out.

Energy content depends on species and on moisture. Dry birch gives about 1,900 kilowatt-hours per stacked cubic metre, oak 2,100, pine 1,500. Freshly cut wood at 50 percent moisture delivers barely half of that, because much of the heat goes into boiling the water off.

What this calculator shows

The firewood required for the season, and per month
The heat that has to be produced over the season, in kilowatt-hours
The cost, if you know the price per stacked cubic metre

What to keep in mind

Average season load is taken at 40 percent of the design output: the hardest frosts never last long.
Energy content is quoted for wood at about 20 percent moisture — a year under cover.

FAQs

How much firewood for a winter?

For an 80 square metre house in a temperate climate, about 12 stacked cubic metres of birch across a seven-month season. The same house in a cold climate wants roughly 17.

What is a stacked cubic metre?

A cubic metre of stacked logs including the gaps. It holds about 0.65 to 0.7 cubic metres of solid timber, so prices per stacked and per solid metre are not directly comparable.

Which firewood is best value?

By heat per volume, oak and ash, then birch. Softwoods give less heat and more tar in the flue, but cost less and dry faster.

Why does wet wood heat so poorly?

Because part of the energy goes into evaporating the water. Wood at 50 percent moisture delivers roughly half the useful heat and clogs the flue quickly.

Worked example

An eighty-metre house on birch

Input: 80 m², temperate climate, birch, 70% efficiency, 7 months

Output: 12.1 stacked cubic metres for the season

Note: About a lorry and a half — the familiar figure for a house that size. Pine in the same house would take 15.3 stacked cubic metres, because its energy content is a quarter lower.

Useful links

All tools in Home & Utilities

Firewood Calculator

Result

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