How to Estimate the Running Cost of a Wood-Burning Stove
A cheap load of logs can become expensive heat if it contains plenty of water or your stove uses it inefficiently. To estimate wood-burning stove running costs, convert the delivered firewood price into a cost per useful kilowatt-hour: the heat the appliance actually releases into your home.
The calculation needs three things: the amount of wood, its energy content at the moisture level when burned, and the stove’s efficiency. Once those are clear, you can compare suppliers and build a realistic seasonal budget.
The basic running-cost formula
Use this formula for the fuel portion of your heating costs:
Fuel cost per useful kWh = delivered firewood cost ÷ (wood mass × energy content × stove efficiency)
Enter:
- Delivered cost in euros, including VAT and delivery.
- Wood mass in kilograms, excluding packaging.
- Energy content in kWh per kilogram at the wood’s burning moisture content.
- Efficiency as a decimal: 75% becomes 0.75.
For example, wood containing 4.0 kWh/kg burned at 75% efficiency supplies:
4.0 × 0.75 = 3.0 useful kWh per kilogram
This distinction matters. The energy contained in the logs is greater than the heat delivered by the stove.
Understand the unit before comparing firewood prices
Firewood offers can look similar while describing very different quantities.
| Sales unit | What it measures | What to check |
|---|---|---|
| Kilogram or tonne | Mass; one metric tonne equals 1,000 kg | Moisture content and whether packaging is excluded |
| Loose cubic metre | Logs tipped into a measured volume, including gaps | Container dimensions and how the volume is measured |
| Stacked cubic metre, sometimes called a stere | A neatly stacked volume, including gaps between logs | Stack dimensions and log length |
| Solid cubic metre | Wood volume excluding air gaps | Whether this is genuinely the supplier’s stated unit |
| Bag, net, crate or pallet | A package rather than a fixed fuel quantity | Net mass, internal dimensions and whether logs are loose or stacked |
A loose cubic metre contains more empty space than a carefully stacked cubic metre. Neither has a universal weight: species, moisture, log size and packing all affect the result.
For the calculation, ask for a credible net mass at a stated moisture content. If only volume is available, request a mass estimate specific to that product and treat the result as approximate. A weighed sample of the actual delivery can help.
Avoid applying a single “kilograms per cubic metre” conversion to every supplier.
Account for moisture content
Water adds weight without adding fuel energy. It also takes energy to evaporate during combustion, reducing the net energy available from each kilogram of logs.
The Dutch government-commissioned report on wood burning identifies 10–20% moisture on a wet basis for stove firewood and explains how excessive moisture disrupts combustion. Follow your appliance manufacturer’s fuel requirements.
Use an energy value that matches the moisture
For a household estimate, about 4.0 kWh/kg at 20% moisture, wet basis, is a useful rounded assumption for ordinary firewood. Actual values vary with wood composition.
A supplier’s credible net calorific value at the relevant moisture level is preferable. Net calorific value, also called lower heating value, accounts for water leaving as vapour.
For an approximate moisture adjustment, you can use:
Energy content ≈ 5.2 × (1 − m) − 0.68 × m
Here, m is wet-basis moisture expressed as a decimal. The formula assumes a dry-wood net energy content of 5.2 kWh/kg. It gives approximately:
- 15% moisture: 4.3 kWh/kg.
- 20% moisture: 4.0 kWh/kg.
These are planning estimates rather than certified fuel specifications. When using a moisture-adjusted energy value, the water penalty is already included; do not subtract it again.
Check what your moisture meter reports
Wet-basis moisture means water mass divided by total log mass. Dry-basis moisture means water mass divided by dry wood mass.
The percentages differ: 25% dry-basis moisture equals 20% wet-basis moisture. Check your meter’s instructions before using its reading in a calculation.
Take readings on freshly split internal faces across several representative logs, following the meter’s guidance. An exposed end alone may not represent the moisture inside.
If you buy wet wood and season it, use its mass and moisture after drying together. Combining the original wet delivery mass with the higher energy content of dried wood overestimates the available heat.
Worked example: a delivered load of logs
Assume the following illustrative figures. They are calculation inputs, not current Dutch market prices:
- Delivered price, including VAT: €240.
- Net wood mass when burned: 500 kg.
- Moisture when burned: 20% wet basis.
- Assumed net energy content: 4.0 kWh/kg.
- Assumed average operating efficiency: 75%.
- All the wood is usable, with no further drying or storage losses.
Step 1: Calculate the price per kilogram
€240 ÷ 500 kg = €0.48/kg
Step 2: Calculate the energy in the load
500 kg × 4.0 kWh/kg = 2,000 kWh of fuel energy
Step 3: Allow for stove efficiency
2,000 kWh × 0.75 = 1,500 useful kWh
Step 4: Calculate the useful heat cost
€240 ÷ 1,500 kWh = €0.16 per useful kWh
The firewood cost per kWh of fuel energy is €0.12. After allowing for stove efficiency, the fuel cost rises to 16 cents per useful kWh.
At an average useful output of 4 kW for four hours, the stove would supply 16 kWh and consume approximately €2.56 of wood under these assumptions.
Choose a realistic efficiency assumption
Use the appliance’s documented efficiency as a starting point, checking that it uses the same net calorific value basis as your fuel figure. A declared test efficiency does not guarantee the same result across repeated lighting, reloading and cooling cycles. A seasonal efficiency figure may also use a different calculation method.
For budgeting, test more than one operating-efficiency assumption. With the same €0.48/kg logs and 4.0 kWh/kg energy content:
| Assumed operating efficiency | Fuel cost per useful kWh |
|---|---|
| 65% | €0.185 |
| 75% | €0.160 |
| 80% | €0.150 |
These scenarios show how sensitive the estimate is to efficiency; they do not predict a particular stove’s performance.
Also consider whether the room needs the heat produced. Heat that causes overheating and open windows adds little value to the household heating budget.
Reusable running-cost worksheet
Copy this table and replace the example inputs with your own figures.
| Item | Symbol or calculation | Example | Your figure |
|---|---|---|---|
| Delivered fuel price, including VAT | P | €240 | _____ |
| Usable wood mass at burning moisture | M | 500 kg | _____ |
| Moisture, wet basis | Record alongside energy value | 20% | _____ |
| Net energy content at that moisture | H | 4.0 kWh/kg | _____ |
| Assumed operating efficiency | η | 0.75 | _____ |
| Useful heat from the load | M × H × η | 1,500 kWh | _____ |
| Fuel cost per useful kWh | P ÷ (M × H × η) | €0.16 | _____ |
| Annual useful heat supplied by stove | Q | 3,000 kWh | _____ |
| Annual fuel cost | Q × fuel cost per useful kWh | €480 | _____ |
| Other annual operating costs | A | €120 assumed | _____ |
| Total annual running cost | Annual fuel cost + A | €600 | _____ |
Keep delivery costs in the fuel price and avoid adding them again under annual operating costs.
Allow for costs beyond logs
Chimney sweeping, servicing, replacement seals, kindling and firelighters can all affect the annual budget. Use actual quotations or receipts; the worksheet’s €120 allowance is purely illustrative.
In the example, €600 divided by 3,000 useful kWh gives a total running cost of €0.20 per useful kWh. Purchase and installation costs would need a separate allowance if you want to compare total ownership costs.
Keep invoices, record how much wood you burn, and note its moisture content. After a heating season, those records will let you replace broad assumptions with figures that reflect your stove and household.