📊 Firewood Heat Values and Stove Efficiency

In short: According to VTT, the Technical Research Centre of Finland, all wood species have almost the same heat value per kilogram: 4.00–4.15 kWh/kg at 20% moisture.

  • The difference between species comes from density
  • Birch gives about 1700 kWh per stacked cubic metre
  • Alder gives about 1230 kWh per stacked cubic metre
  • A masonry heater has 80–85% efficiency, an open fireplace less than 30%
  • Tammaru Farm firewood has 10–15% moisture, so it is drier than in the VTT table
Top-down lighting: logs stacked with air gaps in a fireplace, fire burning on top

Heat values of wood species (20% moisture, VTT data)

Wood specieskWh/kgkWh per loose m³kWh per stacked m³
Birch*4.1510101700
Pine4.158101360
Aspen4.007901330
Spruce4.107901320
Alder*4.057401230

* data for commercial firewood. Wood moisture 20%. Black alder is not listed separately in the VTT table. Source: VTT – Technical Research Centre of Finland (Valtion teknillinen tutkimuskeskus); Alakangas, Erkkilä, Oravainen, «Tehokas ja ympäristöä säästävä tulisijalämmitys», 2008.

Per kilogram, the energy content of all species is almost the same. The difference comes from density: birch is denser and gives noticeably more heat per stacked cubic metre than alder. The drier the wood, the less energy is used to evaporate water.

🛠️ How much heat reaches your room?

According to VTT, it depends on the efficiency of your stove or fireplace:

  • Masonry heater or fireplace stove: efficiency 80–85%. It stores heat in its masonry and releases it gradually.
  • Cooker and sauna stove: efficiency 50–70%.
  • Open fireplace without glass: efficiency less than 30%. Most of the heat goes up the chimney.

📐 How much wood should you burn at one time?

For masonry heaters, VTT recommends about 1 kg of firewood per 100 kg of heater weight per firing.

Example: the heater weighs 1500 kg → 1500 / 100 = 15 kg of firewood per firing. You can split this into two loads, for example 9 kg and 6 kg, so the firebox does not overheat.

🪵 How to heat efficiently?

  1. Use only dry firewood. Bring the logs indoors 1–2 days before heating to reduce surface moisture.
  2. Remove the ash before lighting and open the damper and air vents fully.
  3. Stack the logs with air gaps. Fill the firebox up to 2/3, as advised by the Estonian Rescue Board (Päästeamet).
  4. Put birch bark or kindling on top and light from the top. This produces less smoke when lighting.
  5. Add a new batch of wood when the previous logs have almost burned down to embers.
  6. Close the damper only when the embers have burned out and there are no flames above them, not even blue ones.

Full guide: Dry firewood: how to heat efficiently

📦 Where can you get dry firewood?

Tammaru Farm firewood is kiln-dried, and the 10–15% moisture is checked before packing. Birch is denser and gives more heat per stacked cubic metre, while alder is lighter. Log lengths are 25, 30 and 40 cm, in mesh bags of 20, 40 and 60 litres. We deliver in Tallinn and Harjumaa, usually within 1–3 working days.

Orders: +372 52 388 52. We speak Estonian, Russian and English.

Sources: VTT – Tehokas ja ympäristöä säästävä tulisijalämmitys (2008); Estonian Rescue Board (Päästeamet)

Updated: 19 October 2026