How much firewood do I need for a winter?
It depends on four things you can count: how many evenings a week you light the stove, how long it burns, the heat output you run it at, and how many weeks your season lasts. Multiply those to get the heat you need, then divide by the useful heat in a kilo of your logs. Drier logs mean fewer kilos.
How it works
The sum has two halves.
The heat you use. Evenings a week × hours each evening × the stove's output in kW × weeks in the season gives kilowatt-hours (kWh). Four evenings a week, four hours at a time, at 5 kW over 26 weeks comes to 2,080 kWh from the stove.
The heat in your logs. Every kilo of wood holds a certain amount of energy when it's bone dry. Water in the log costs you twice: it isn't wood, and some of the fire's heat goes on boiling it off. So the energy in a kilo falls as the moisture content rises. Your stove then turns only part of that energy into heat in the room: that's its efficiency, printed on the spec plate or in the manual.
Divide the heat you use by the useful heat per kilo and you have kilos of logs for the season.
From kilos to cubic metres and bags
Log sellers rarely sell by weight. They sell by the cubic metre, the bulk bag or the net, and those aren't the same thing:
- Stacked cubic metre: logs stacked neatly in a 1 m × 1 m × 1 m space.
- Loose cubic metre: logs tipped into the same space. More air, fewer logs.
- Bulk bag: bag sizes vary from seller to seller, so check theirs.
To turn kilos into volume you need your logs' weight per stacked cubic metre, which depends on the species and how dry they are. Ask your supplier, or weigh a crate of known size. See how much a cubic metre of logs is.
Buying and storing
- Order early. Logs bought in late summer can be stacked and checked before you need them. See order your logs in September.
- Buy dry, or buy ahead. Check the moisture with a meter on a freshly split face. Wet logs can be seasoned, but not in time for this winter.
- Leave room for next year. If you season your own, your store needs space for this winter's logs and next winter's. See log store size.
Mistakes to avoid
- Using the stove's maximum output. Use the output you actually run it at.
- Assuming "a bag a week". Your evenings, your stove and your logs set the figure.
- Comparing loose and stacked prices. A loose cubic metre holds fewer logs than a stacked one.
- Forgetting the moisture. Wet logs give less heat per kilo, so you burn more.
FAQs
How much firewood do I need for a winter?
Work it out from your evenings a week, hours per evening, stove output and season length, then divide by the useful heat in your logs. Our firewood calculator does it and shows each step.
How many logs do I burn in an evening?
Divide the heat for one evening (output in kW × hours) by the useful heat in a kilo of your logs. It varies with your stove, your logs and how you run it, so a season's log-use tracker beats any rule of thumb.
Is a cubic metre of logs enough for a winter?
Only if your sum says so. Check whether the cubic metre is stacked or loose, then compare it with the volume our calculator gives for your evenings.
Do dry logs really go further?
Yes. Water in a log adds weight but no heat, and some of the fire's heat goes on boiling it off. Logs at or below 20% moisture give more heat per kilo.