❄️ Winter Wood Supply Estimator

Estimate how many cords of firewood you'll need to get through a full heating season, based on your stove's output, usage pattern, and wood type.

Burn hours per day

Heating season length (days)

Stove output (BTU/hr)

Stove efficiency (%)

Wood's million BTU per cord

The season total, step by step

Burn hours, season length and stove rating give the heat you want in the room. That is divided by the stove's efficiency to get the energy the wood must hold, then by the heat in one cord of your species:

wood BTU = hours/day × days × stove BTU/hr ÷ efficiency
cords    = wood BTU / (million BTU per cord × 1,000,000)

The loaded defaults — 6 hours a day for 120 days on a 40,000 BTU/hr stove at 65 percent, burning 25.7 million BTU oak — come to 44,307,692 BTU and 1.72 cords. That is an evening fire through a single season, not a whole house.

What the efficiency box is doing

The stove figure here is rated output to the room, so efficiency divides it up rather than down: at 65 percent, every 100 BTU of wood delivers 65 to the room, and you must burn more wood than the room receives. Set efficiency to 100 only if your rating is the wood energy going in rather than the heat coming out — that reads 1.12 cords on the same defaults.

Burn hours are a season average. Two hours in October and sixteen in January average out; enter the average, not a cold-snap day.
Million BTU per cord takes the seasoned figure for your species: 25.7 for white oak, 24.0 sugar maple, 15.9 ponderosa pine. Those assume wood dried to about 20 percent moisture, so add a margin if yours is damp.
Buy by the full cord, 128 cubic feet. A quote in face cords or ricks means nothing until you ask the log length, since the seller defines it.

Frequently asked questions

How many cords of wood do I need for winter?

Three to five for a house heated on wood alone. Burning around the clock for 90 days on a 40,000 BTU/hr stove at 65 percent efficiency works out at about 132.9 million BTU of wood, or 5.2 cords of oak. Weekend and evening burning is far less — the defaults here come to 1.72 cords.

How long does a cord of wood last?

A cord of oak holds 25.7 million BTU. The evening-fire pattern loaded here burns 44.3 million across the season, so one cord covers a little under two thirds of it. A stove running flat out goes through a cord in about a month.

Does wet wood change how much I need?

Yes. Published BTU figures are for wood at roughly 20 percent moisture. Green wood spends part of its energy boiling off water, so plan on burning noticeably more volume for the same warmth.