How many gallons of oil does a cord of wood replace?
A cord of seasoned hardwood gives the same heat as roughly 150 gallons of heating oil once you count what a wood stove and an oil boiler each lose up the flue. The exact number depends on the species and on both efficiencies, so set them below. Add the cords you burn in a winter to see the oil you would not have to buy.
The arithmetic
heat in the house from a cord = million Btu × stove efficiency
heat in the house from a gallon = 138,500 Btu × boiler efficiency
gallons replaced = the first ÷ the second
The question only makes sense if both fuels deliver the same heat to the rooms, so the efficiencies belong in the sum. A stove and a boiler waste different shares, which is why the answer is lower than the raw comparison on the line under the big number. The default efficiencies are Efficiency Maine's: 73% for a wood stove and 87% for an oil boiler (Efficiency Maine heating cost calculator). The oil figure of 138,500 Btu per gallon is the U.S. Energy Information Administration's (EIA Btu conversion factors).
Worked example
Red oak is 25.3 million Btu a cord. Through a 73% stove that is 25.3 × 0.73 = 18.47 million Btu in the house. A gallon of oil through an 87% boiler is 138,500 × 0.87 = 120,495 Btu. Dividing gives 153.3 gallons a cord. Three cords is about 460 gallons, which at the $5.97 example price on the fuel cost comparison is about $2,745 of oil. The three cords are my illustration, not a typical winter.
Gallons replaced by species
Heat contents are the Missouri Department of Conservation's table of basic heating value per cord. The last column uses the default efficiencies (73% stove, 87% boiler); the form above uses yours.
| Species | Million Btu per cord | Gallons at 100% both ends | Gallons replaced at defaults |
|---|---|---|---|
| Red oak | 25.3 | 182.7 | 153.3 |
| White oak | 27.0 | 194.9 | 163.6 |
| Hickory | 29.1 | 210.1 | 176.3 |
| Ash | 23.6 | 170.4 | 143.0 |
| Elm | 21.4 | 154.5 | 129.6 |
| Shortleaf pine | 19.0 | 137.2 | 115.1 |
| Cottonwood | 16.1 | 116.2 | 97.5 |
Why sources give different numbers
A cord is a volume, 128 cubic feet of stacked wood, so its heat depends on what is in the stack. The sources I opened disagree for that reason, and for a few others:
| Source | Million Btu per cord | What it describes |
|---|---|---|
| EIA | 20.0 | A general figure for a cord of wood |
| Maine weekly price tables | 22 | The figure their price conversions work out to |
| Wikipedia, Cord (unit) | 22.1 | One seasoned cord of Northern red oak |
| Efficiency Maine | 25 | Its firewood row in the heating cost calculator |
| Missouri Dept. of Conservation | 25.3 | Red oak, basic heating value |
Wikipedia's article pairs its 22.1 million Btu red oak cord with "the heating equivalent of 159 U.S. gallons ... of fuel oil with a heating value of 138,700 British thermal units per U.S. gallon" (Wikipedia, Cord (unit)). That is the raw comparison at 100% on both sides. This page's raw column for the same wood, with the Missouri table's 25.3 and EIA's oil figure, is 182.7 gallons. The gap is the heat content: 22.1 against 25.3 million Btu for red oak. My guess is that it comes from moisture and how the stack was measured, but neither source says. The Missouri table notes that how much heat you get "very much depends on the efficiency of the stove, fireplace or furnace where you burn it" (Missouri Department of Conservation, Home Heating), which is the reason for the two efficiency fields here. EIA's 138,500 and Wikipedia's 138,700 Btu per gallon of oil differ by 0.14%, too little to matter.
What the number leaves out
- My suggestion: type a lower heat content than the species table if the wood is not fully seasoned. Wikipedia's figure is for a seasoned (dry) cord, and the Missouri table does not say how dry its wood was.
- A cord that is a "face cord" or a truck load is smaller than 128 cubic feet. Ask the seller what the stack measures.
- An open fireplace sends most of its heat up the chimney, so the stove efficiency field is not meant for one. Missouri's article says so too. 73% is the wood stove default in Efficiency Maine's calculator (checked October 18, 2026).
- Wood heat usually warms one room or one floor. Whether it displaces oil gallon for gallon depends on how much the boiler still runs, which the gallons per day on the oil usage page will show.
- For dollars per million Btu of heat, with cordwood next to oil, propane, pellets and electricity, use the heating fuel cost comparison.
Related
- Heating fuel cost comparison: cost per million Btu delivered for seven fuels.
- How long will heating oil last? Days left from two dated dips.
- Heating oil use per month: a yearly total split by month.
- Oil tank calculator: inches on the stick to gallons.