Firewood BTU Calculator

Wet wood is the single biggest BTU killer on this page, bigger than species choice and bigger than stove rating. Target is under 20% moisture ^{[4] [4] [4]} content.

split a piece open and read the fresh face, not the weathered outside. The outside of a green split reads dry and lies to you. Under 20% ^[4]is ready, 20% to 25% is marginal ^[4], above 25% ^[4]means it is next year's wood.

the checks stack up. Seasoned splits are lighter than they look, have checking cracks at the end grain, and knock together with a sharp clack instead of a dull thud.

Bark that slips off easily is a good sign. A cold, heavy end grain that smells green is a bad one.

Do this before you unload the truck, not after. A meter pays for itself the first time it saves you from a cord of green oak.

An oversized stove is not free insurance. Put a 3.0 cubic foot firebox in a house that needs 1.6 and you will spend the winter running it choked down, because a full load at full output makes the room unbearable.

Choked down means low firebox temperature, so the secondary combustion the stove was certified on never engages.

You get incomplete combustion, unburned gas going up the flue as smoke and creosote, and real efficiency well below the label on an appliance rated in the seventies.

A correctly sized stove running at 75% of capacity ^[3] holds temperature, burns clean, and delivers the efficiency on the label. Size to your heat load, not to your worst imagined night, and handle the cold snap with an extra reload instead of a bigger box.

A cord is a volume measurement: 128 cubic feet of stacked wood, 4 feet by 4 feet by 8 feet. That number never changes. What changes is what is inside the stack. A cord of hickory and a cord of white pine occupy identical space on your rack, and the hickory carries roughly 74% more heat.

That gap is why price per cord tells you almost nothing on its own. The EIA's biomass data puts hickory at 27.7 MMBTU per cord and white pine at 15.9. Buy both at $250 and you paid $9.03 per MMBTU for one and $15.72 for the other. Same money, same stack size, wildly different winters.

So the unit that matters is MMBTU per cord, then MMBTU delivered after your stove takes its cut. Everything below works from those two numbers.

A face cord is one row 4 feet tall and 8 feet long, depth equal to whatever the seller cut. At 16 inch splits that is one third of a cord.

Priced at $150 it sounds like a deal until you divide: $450 per full cord. Ask for the split length before anything else.

All values are MMBTU per cord of well seasoned wood, sourced from EIA fuel heat content tables. The "best for" column is where each species actually earns its keep in a stove.

Notice the middle of the table is crowded. Sugar maple to ash is a 20% ^[1] spread across four species.

If your local yard has maple at $200 and oak at $290, the maple wins on heat per dollar even though oak sits higher on the chart.

Osage orange tops most published BTU charts at values above 30 MMBTU per cord, and you will never see it stacked at a Vermont wood yard. Same for mesquite outside the Southwest.

Rank the species you can actually buy within a 30 mile haul. Trucking firewood any farther eats the savings and moves pests across quarantine lines.

EPA certified stoves run between 63% ^[3] and 83% ^[3] efficiency depending on design, per EPA Burn Wise. That range is worth more than your species choice, and almost nobody comparison shops it.

Run the numbers on three cords of red oak, 73.8 MMBTU in the stack:

• 63% efficient ^[3] stove: 46.5 MMBTU delivered
• 75% efficient ^[3] stove: 55.4 MMBTU delivered
• 83% efficient ^[3] stove: 61.3 MMBTU delivered

The spread between the worst and best certified stove is 14.8 MMBTU: roughly 0.6 cords of oak bought, hauled, split, stacked, and sent up the chimney.

Upgrading from red oak to hickory across those same three cords buys you 9.3 MMBTU of raw input, less after stove losses. The stove wins.

Older uncertified stoves and open fireplaces are worse than the bottom of that range. A masonry fireplace can run near zero net efficiency once you count the heated indoor air it pulls up the flue. If you are burning in one and wondering why the cord count keeps climbing, that is the answer.

Freshly cut wood carries 40% ^[4]to 60% moisture by weight ^[4]. Every pound of that water absorbs heat to boil off before the wood contributes anything.

The resulting steam carries more heat out the flue. Net loss on unseasoned wood runs 20% to 30% of usable output ^[4], before counting the creosote you are laying down in the chimney.

Put it in money. Three cords of red oak at $280, sold seasoned, is $840 for 73.8 MMBTU. The same yard offers green at $220, so $660. Feels like $180 saved.

Burn it wet at a 25% penalty ^[4] and those three cords deliver 55.4 MMBTU instead of 73.8. Your effective cost is $11.91 per MMBTU on green wood versus $11.38 on seasoned.

You paid less and got less at a worse rate. Add the chimney sweep you now need mid winter and the math turns clearly negative.

Green wood is only a bargain when you buy it in spring for the winter after next. At that point you are paying green prices for wood that will be seasoned when it matters, which is the actual play.

The formula is short: cord price divided by MMBTU per cord equals cost per MMBTU. Do it for every quote you get and the wide $150 to $400 spread you have seen advertised collapses into a ranking you can act on.

On raw heat per dollar the softwood wins here and hickory loses. That is real, and it is also incomplete.

Softwood at 18 MMBTU per cord means more cords stacked, more handling, more reloads, and no overnight coal bed. You are paying the hickory premium for burn duration and reload frequency, not for BTUs.

Compare against your alternative fuel the same way. Propane runs about 0.0915 MMBTU per gallon at roughly 90% furnace ^[5] efficiency, so at $3.20 a gallon you are near $38.85 per delivered MMBTU.

Red oak at $280 a cord through a 75% stove ^[3] lands near $15.18 delivered. State heating fuel price surveys such as Maine's DOER tracker publish current propane and oil numbers you can plug straight in.

Plug your cord price into the firewood cost calculator to find your cheapest source of heat per dollar.

Dense hardwood is for burns you will not be attending. Hickory, white oak, and red oak have the mass and coal structure to hold a firebox for six to eight hours, which is what gets you from 10pm to a warm house at 6am without setting an alarm to reload.

Lighter woods are for burns you are standing next to. Birch, ash, and the softwoods light fast and burn out in two to four hours.

That is exactly what you want on a 45 degree October afternoon when a full oak load would drive you out of the room and smolder for hours after you no longer need it.

Practical split of a three cord season for a 1,500 square foot house: two cords of dense hardwood for December through February overnight loads, one cord of lighter wood for October, November, March, and April daytime burns.

Buying three cords of oak and burning it in shoulder season is how people end up choking the stove down, which drops efficiency and coats the flue.

Wood dries at very different rates, and the dense species that carry the most heat are the slowest. Split, stacked off the ground, top covered, sides open to wind:

• Red oak and white oak: 12 to 24 months. Oak holds water stubbornly. A single summer is not enough.
• Hickory, sugar maple, birch: 9 to 18 months.
• Ash: 6 to 12 months. Ash starts low on moisture and burns acceptably at the shorter end, which is why it has a reputation for burning green. It still burns better dry.
• Pine, fir, and other softwoods: 3 to 6 months. Cut in spring, burn in fall.

The most common firewood mistake is buying green oak in September for a December that is already spoken for.

It will not be ready. It will hiss, it will not hold temperature, and you will burn through more cords chasing the heat you paid for.

My neighbor did this with four cords of red oak from a tree service in October, $180 a cord because it had been on the ground three weeks.

By January he was buying a cord of kiln dried at $420 to mix in so the stove would run at all. The oak was excellent the following winter, just not that one.

Stack it now for next year, and you buy at spring prices instead of January panic prices.

A single load can use two species on purpose. Build with the light stuff, sustain with the heavy stuff.

1. Kindling and start: pine or fir splits, wrist thick. High resin, low density, catches fast and gets the flue drafting.
2. Establish: two or three medium birch or ash splits. These bring the firebox up to operating temperature quickly, which is where the stove's secondary combustion actually works.
3. Sustain: once you have a real coal bed and the stovetop is up to temperature, load the oak or hickory. Dense wood on a hot coal bed gasses off properly. Dense wood on a cold start smolders, and smoldering is where efficiency and your chimney both go to die.

This is also the cheapest way to run a season. Your softwood is doing the job that softwood is good at, at $165 a cord, instead of you burning $340 hickory to light a fire.