How many cords of firewood do I need?

How this calculation works

It runs in three steps. First, how much heat your house needs for a season: square footage multiplied by a per-square-foot seasonal load for your climate, adjusted for how leaky the building is. Then how much of that the wood is expected to carry — all of it if the stove is your only heat, less if a furnace picks up the cold nights. Finally, how much heat one cord of your wood actually delivers into the room, which is where most of the interesting losses live.

That last step is the one other calculators skip. A cord of white oak holds about 27.9 million Btu. Burned in a modern stove at 70% efficiency, roughly 19.5 million reaches the room. Burned in an open fireplace, under 3 million does. Same wood, same cord, a factor of seven in what you get out of it.

Hardwood and softwood carry the same heat per pound

This is the piece that surprises people. Per pound, oak and pine are nearly identical — around 8,200 Btu for hardwood and about 8,600 for resinous softwood. Pine is slightly ahead. All wood is mostly cellulose and lignin, and burning a pound of it releases about the same energy regardless of what tree it came from.

The gap between species is density, and nothing else. A cord of white oak weighs about 3,392 lb; a cord of white pine weighs about 1,744 lb. You are buying a fixed volume — 128 cubic feet — so the oak cord simply contains twice as much wood. That is the whole story behind the heat table.

The practical consequence is about price rather than fuel quality. If oak and pine cost the same per cord, the pine is nearly twice as expensive per unit of heat. But pine at half the price is a perfectly rational buy, and it dries in six months instead of two years. Pine is not bad firewood — it is a smaller amount of firewood per cord.

One real caveat: resinous softwoods burn faster and hotter, so a stove loaded with pine needs reloading more often and will not hold coals overnight. For a shoulder-season fire that suits fine. For a January night, density is convenience.

Green oak is no better than dry pine

Freshly cut wood can be half water by weight. That water does not burn — it has to be boiled off first, and the heat doing the boiling comes out of the fire and goes up the chimney as steam. The Department of Energy puts the loss at up to 50% for green wood.

Run the arithmetic and it lands somewhere uncomfortable. A cord of unseasoned white oak, the best fuel on the list, delivers about the same usable heat as a cord of seasoned white pine, the worst. Every advantage you paid for in the species is spent on evaporating water. At the pessimistic end of DOE's range the oak comes out behind.

So the ranking most people carry around — oak good, pine poor — is only true if both are dry. Given a choice between green premium hardwood and seasoned softwood at the same price, take the dry wood. Given green hardwood cheap, buy it and burn it next year.

Wet wood costs more than heat, too. Unburned volatiles condense in a cooler flue as creosote, which is what chimney fires are made of. A stove that will not hold a fire, glass that sooties over within a day, and hissing splits are all the same diagnosis.

Seasoning times vary more than people expect, and oak is the outlier: two years split and stacked, not one. Ash is the opposite — often ready in nine months, which is why cutters like it. Split first, then stack off the ground with the top covered and the sides open. Rounds left whole barely dry at all, because bark is designed to keep water in.

The face cord trap

A full cord is a defined quantity: 128 cubic feet, stacked 4 ft high, 4 ft deep and 8 ft long. It is the only measure with a legal definition in most states.

A face cord— also sold as a rick or a rack — is 4 ft high and 8 ft long, but only one row deep. With the common 16 in split that is about a third of a full cord. Buy three face cords and you have one cord, so a "cord" advertised at a third of the going rate is not a deal, it is a different unit.

Two things to insist on. Ask the split length: a face cord of 12 in splits is a quarter of a cord, not a third, and the same price buys visibly less. And take delivery of stacked wood or stack it yourself before paying — a thrown pile of wood in a truck bed cannot be measured, and a loose heap occupies far more space than the same wood stacked.

Heat value by species

Million Btu per full cord at 20% moisture, from the University of Kentucky Forestry Extension's firewood table, with typical seasoning times:

Top to bottom is nearly a factor of two, which is worth knowing when someone offers you a cord of mixed wood at a hardwood price. But note that sugar maple gives up only 7% against white oak while drying in half the time — for most people that is the better buy.

What this calculator can't tell you

It cannot see your actual building. Square footage is a crude stand-in for heat load: ceiling height, window area and orientation, and whether the stove sits in an open plan or behind three doorways all matter, and the last one matters a lot. A stove heats what air can circulate to. Two identical houses can differ by a cord on layout alone.

It also cannot predict a winter. A cold snap or a mild February moves this by 20% in either direction, which is the real argument for buying a season ahead: you get dry wood and a buffer at the same time. Every experienced burner runs a surplus, and it is not caution — it is how the wood gets dry.

Stove efficiency here is a category, not your unit. A published EPA figure is measured under test conditions with a particular fuel load, and how you run the stove — damper settings, load size, whether you let it smoulder — swings the real number substantially. Chimney height and draft matter too. Treat the result as a starting quantity and correct it against what you actually burn in your first season.

One thing worth knowing that is not in any of the arithmetic: insulating and air-sealing reduces the wood pile permanently, and it is usually cheaper per unit of heat than buying more cords every year. The tight-versus-leaky setting spans nearly two to one for a reason.

The rest of getting ready for winter

Wood and food run on the same calendar — both want to be handled in the fall and both punish you for starting late. The root cellar calculator sizes the vegetable side of the same season, and the food storage planner covers the dry goods. Whatever you work out here is saved on your my homestead page.