Calculate how many cords of firewood you will use per heating season from home size, climate, insulation, wood species, and stove efficiency, or find how long your firewood supply will last.
Firewood Usage Formula
- Cords = full cords of firewood used per heating season (1 cord = 128 cubic feet of stacked wood)
- A = heated floor area in square feet
- HDD = heating degree days for your location and season
- I = insulation factor in BTU per square foot per HDD (3 for excellent insulation up to 7 for poor)
- S = share of your heating done with wood, as a decimal (1.0 if wood is your only heat)
- B = heat content of the wood in BTU per cord (about 22,000,000 for mixed hardwood)
- E = appliance efficiency as a decimal (0.75 for an EPA-certified stove, 0.12 for an open fireplace)
- M = moisture factor (1.0 for well seasoned wood, 0.85 partly seasoned, 0.6 green)
The seasonal mode multiplies your home’s area by heating degree days and the insulation factor to estimate the total heat your home needs, then divides by the usable heat delivered per cord after appliance efficiency and seasoning losses. The burn rate mode skips the heat model and instead multiplies the wood you actually burn per day by the number of heating days:
- R = wood burned per day in cubic feet
- D = heating days in the season
The supply duration mode divides the stacked volume of wood you have on hand by your daily usage to tell you how many days, weeks, and months your firewood will last.
Heat Content by Species and Fuel Cost Comparison
Denser species pack more heat into each cord, so your usage in cords drops as the wood gets heavier. The table shows seasoned heat content and how many cords match the heat of one cord of white oak.
| Species | Million BTU per cord | Cords to equal 1 cord of white oak |
|---|---|---|
| Hickory | 27.7 | 0.93 |
| Black locust | 26.8 | 0.96 |
| White oak | 25.7 | 1.00 |
| Red oak | 24.6 | 1.04 |
| Sugar maple | 24.0 | 1.07 |
| Ash | 23.6 | 1.09 |
| Mixed hardwood | 22.0 | 1.17 |
| Douglas fir | 20.6 | 1.25 |
| Pine | 16.2 | 1.59 |
Usage in cords only tells you half the story. The comparison below converts firewood and other common heating fuels to cost per million BTU of heat actually delivered into the room, after typical appliance efficiency. It lets you judge whether burning more wood or leaning on a backup system is cheaper for your situation.
| Heat source | Assumed price | Efficiency | Cost per million BTU delivered |
|---|---|---|---|
| Firewood, self-cut | $75/cord (permit, fuel, gear) | 75% | about $4.50 |
| Firewood, delivered hardwood | $300/cord | 75% | about $18 |
| Heat pump | $0.16/kWh | COP 3.0 | about $16 |
| Natural gas furnace | $1.50/therm | 95% | about $16 |
| Heating oil | $3.60/gal | 85% | about $31 |
| Propane | $2.80/gal | 92% | about $33 |
| Electric baseboard | $0.16/kWh | 100% | about $47 |
Prices vary widely by region and year, so rerun the math with your local numbers, but the ranking is fairly stable: self-cut wood and heat pumps are cheapest, delivered hardwood competes with natural gas, and burning wood in an open fireplace (12% efficient) is more expensive per delivered BTU than almost any alternative.
Firewood Usage Example Problems
Example 1: Seasonal usage. You heat an 1,800 square foot home in a cold climate (6,000 HDD) with average insulation (factor 5), burning well seasoned red oak in an EPA-certified stove.
Total heat required = 1,800 x 6,000 x 5 = 54,000,000 BTU. Usable heat per cord = 24,600,000 x 0.75 = 18,450,000 BTU. Cords = 54,000,000 / 18,450,000 = 2.93 full cords, or about 8.8 face cords. Plan to buy 3.5 cords to keep a reserve.
Example 2: How long will the pile last. You have 3 full cords stacked (3 x 128 = 384 cubic feet) and burn about 2.5 cubic feet per day.
Days = 384 / 2.5 = 153.6, so the supply lasts about 154 days, roughly 22 weeks or 5 months. If your heating season runs 6 months, you should line up about another cord.
FAQ
What is the difference between a full cord and a face cord?
A full cord is a stack 4 feet high, 4 feet deep, and 8 feet long, or 128 cubic feet. A face cord is the same 4 by 8 foot face but only one log deep. With standard 16 inch logs a face cord is about 42.7 cubic feet, one third of a full cord. Always confirm which unit a seller means, because the price difference is large.
How much does burning green wood increase usage?
Unseasoned wood can hold 40 to 50 percent moisture, and a large share of its energy goes into boiling off that water instead of heating your home. The calculator applies a 0.6 factor for green wood, which means you burn roughly two thirds more volume for the same heat, and you also build creosote in the chimney faster. Splitting and stacking wood 6 to 12 months ahead, down to under 20 percent moisture, is the cheapest efficiency upgrade available.
How many cords does a typical home use per winter?
A well insulated 1,500 to 2,000 square foot home heated primarily with an efficient wood stove typically uses 2 to 4 full cords in a moderate to cold climate. Poor insulation, an older stove, severe climates, or an open fireplace can push usage to 6 cords or more. Homes that only burn wood on evenings and weekends often use 1 cord or less per season.