The comparison most sellers hope you won't run
Every heat source reduces to the same unit: dollars per million BTU of heat into the room. Wood at $250/cord of red oak through a modern stove is 250 ÷ (24.6 × 0.75) ≈ $13.55/MBtu. Propane at $2.80 through a 95% furnace is 2.80 ÷ 0.0869 ≈ $32.23. Resistance electric at 14¢ is $41.03 — but the same electricity through a heat pump at COP 3 is $13.68, which is why the modern rival to your woodpile isn't the propane truck, it's the heat pump.
Two traps in wood-heat math. First, double-counted efficiency: some published tables list "available heat" with a stove efficiency already baked in — multiply those by your stove's efficiency and wood looks 25–50% better than it is. Our species numbers are heat content of dry wood (Utah State's table), with efficiency applied exactly once, visibly. Second, moisture: green wood spends its first hours boiling off water — season it or lose a chunk of every number above.
Putting every fuel in the same unit
Fuels are sold in units chosen for the convenience of the seller, not for comparison. Wood comes by the cord, propane by the gallon, natural gas by the therm or the hundred cubic feet, heating oil by the gallon, pellets by the ton, electricity by the kilowatt-hour. None of those units tells you anything about heat until you convert.
The conversion is straightforward and uses published constants. A gallon of propane contains 91,452 Btu. A therm of natural gas is 100,000 Btu by definition. A kilowatt-hour is 3,412 Btu, which is a physical constant rather than an estimate. Heating oil runs about 138,500 Btu per gallon. A cord of firewood depends entirely on species, which is the subject of the next section.
Divide the price by the heat content and you get dollars per Btu; multiply by a million and you have dollars per million Btu, which is the number that lets a cord and a kilowatt-hour argue with each other on equal terms. Then divide by the efficiency of the appliance that will burn it, because the fuel's energy and the heat that reaches your living room are not the same quantity.
Species is most of the value in a cord
A cord is a volume — 128 cubic feet of stacked wood — so buying a cord tells you nothing about how much heat you bought. Dense hardwoods carry far more energy in the same stack than light softwoods, and the spread is close to a factor of two.
Using Utah State University Forestry Extension's figures for dry wood, white oak runs about 29.1 million Btu per cord, sugar or hard maple about 25.5, red oak about 24.6, American elm about 20.0, quaking aspen about 18.2, ponderosa pine about 16.2, and cottonwood about 15.8. So a cord of white oak and a cord of cottonwood are the same purchase by volume and nearly a two-to-one difference in heat. If cottonwood is being offered at ten percent less than oak, it is not a deal.
This is also why "mixed hardwood" as a description is worth discounting. It can mean oak and hickory, or it can mean elm, box elder and whatever came down in the last storm. If you cannot identify what is on the truck, assume the middle of the range and pay accordingly.
The two traps in wood-heat math
The first is double-counted efficiency. Some widely circulated heat-value tables publish "available" Btu per cord with a stove efficiency already applied — often 50 or 60 percent. If you take one of those figures and multiply it by your stove's efficiency, you have applied the discount twice, and wood will look 25 to 50 percent cheaper than it is. The species figures on this page are the heat content of the dry wood itself, with no appliance efficiency baked in, and the efficiency you enter is applied exactly once, visibly. If you are comparing against a number you found elsewhere and the two disagree by roughly a factor of two, this is almost always why.
The second is moisture. Green firewood can be half water by weight, and every pound of that water has to be boiled off inside your stove before the wood burns properly. That energy comes out of the fuel and goes up the chimney as steam, and it drops the flue temperature enough to promote creosote as well. The published heat values assume dry wood — roughly 20 percent moisture, which for most species means split and stacked under cover for a full season, and longer for oak. Burning green wood does not just cost you efficiency; it costs you the chimney.
Appliance efficiency, honestly
Efficiency is where a lot of comparisons go soft, so use realistic numbers rather than nameplate ones. An old, uncertified airtight stove is often in the 50 to 60 percent range in real use. A modern EPA-certified stove is typically 70 to 80. An open masonry fireplace can be close to zero net, and in a drafty house it can be negative — it pulls more heated household air up the chimney than the fire delivers to the room.
On the fossil side, a modern condensing gas furnace is 90 to 97 percent, an older atmospheric one 78 to 82. Electric resistance heat, whether baseboard or a furnace element, is essentially 100 percent at the point of use. A heat pump is the exception to the whole framework, because it moves heat rather than making it: at a coefficient of performance of 3 it delivers three units of heat per unit of electricity, which is 300 percent by this accounting. COP falls as it gets colder outside, so a heat pump that runs at 3.5 in November may be at 2 in a cold snap, and cold-climate comparisons should use the lower figure.
The practical upshot in the numbers above is worth stating plainly: the modern competitor to a woodpile is not the propane truck, it is the heat pump. Wood still wins on cost when you cut your own, and it wins outright when the power is out — but a comparison that only looks at wood versus propane is fighting the last decade's fight.
What the dollar figure leaves out
Cost per million Btu is the right first comparison, and it is not the whole decision. Wood carries labor that the other fuels do not — cutting, splitting, stacking, hauling in, ash out — and if you cut your own, the fuel is nearly free but the hours are not. It carries risk, both from the saw and from the chimney, and an annual sweep is a real recurring cost. It requires storage space and a season of lead time, since wood you buy in October to burn in November is the wrong wood.
Against that, wood heats when the grid is down, the price does not spike with a cold snap, and on a woodlot you are already managing it is a byproduct of work you would do anyway. Those are legitimate reasons to burn wood at a cost per Btu that loses on the spreadsheet. What the spreadsheet is for is knowing by how much, so the choice is made with the number in hand rather than around it.
Planning quantity rather than price? The firewood calculator estimates cords per winter for your house and climate.