A simple formula
1 kg of pellets with a calorific value of 16.5 MJ/kg gives about 4.6 kWh of heat. Allowing for boiler efficiency (about 90%):
Pellets (t) = annual heat demand (kWh) ÷ (4.6 × 0.9) ÷ 1,000
Table
| Annual heat demand | Pellets | 15 kg bags |
|---|---|---|
| 10,000 kWh | ≈ 2.4 t | ≈ 161 |
| 15,000 kWh | ≈ 3.6 t | ≈ 242 |
| 20,000 kWh | ≈ 4.8 t | ≈ 322 |
| 25,000 kWh | ≈ 6.0 t | ≈ 403 |
| 30,000 kWh | ≈ 7.2 t | ≈ 483 |
Figures are approximate. Keep a 10–15% reserve for a cold winter.
How to find your heat demand
- From your previous fuel: 1 m³ of natural gas ≈ 10 kWh, 1 litre of heating oil ≈ 10 kWh. Multiply by your annual use.
- From floor area: a renovated house often needs about 100–150 kWh/m² a year, older houses more. This is only a rough guide.
- Ask your boiler installer for an estimate based on the house and boiler.
Storage
One tonne of pellets takes up about 1.5 m³. 15 kg bags suit smaller amounts; for larger needs big bags are more practical. See 15 kg bags and big bags.
Frequently asked questions
How many kWh does a tonne of pellets give?
About 4,600 kWh at 16.5 MJ/kg. In the boiler you actually get about 4,100–4,300 kWh, depending on efficiency.
How many pellets does a 150 m² house need?
If the house needs about 20,000 kWh a year, it needs roughly 4.8 t of pellets, or about 320 bags of 15 kg.
How much space does a tonne of pellets take?
About 1.5 m³.
Any questions?
Call +370 686 06149, email vladas@biowood.lt or use the contact form.