Short answer: there's no single number. It comes down to three things: how efficient your boiler is, what wood you burn, and how much space you heat.
1. The boiler
Outdoor boilers range from about 40% to 90% efficient. A gasification boiler like the G Series can burn up to 50% less wood than a traditional boiler.
2. The wood
- Oak, ash, hickory: the most heat, about 16 million BTUs per dry cord
- Elm, maple: about 12 million BTUs per dry cord
- Aspen, box elder, willow: as low as 9 million BTUs per dry cord
Dry wood matters too. Wet wood can waste up to 40% of its heat just boiling off water, so cut a year ahead if you can.
3. What you're heating
A bigger space, poor insulation, colder weather, or a long underground line all mean more wood. An old drafty farmhouse can burn more than a big, well-insulated new home.
Want to burn as little as possible? Get an efficient boiler and good underground line. Try our size calculator or ask us.