Cords, face cords and stacked volume
Firewood in the US is sold by the cord. A full cord is a neat stack 8 feet long, 4 feet high and 4 feet deep, or 128 cubic feet including the air between the logs. A face cord (also called a rick or stove cord) is 8 feet by 4 feet but only one log deep. With 16-inch logs, a face cord is one third of a full cord.
- Stacked volume (ft³) = length × height × log length (in feet)
- Full cords = stacked volume ÷ 128
Sellers often use “cord” loosely, so ask for the dimensions of the stack before you buy.
Heat content by species
Dry wood of every species holds about the same energy per pound, but dense hardwoods pack more pounds into a cord. That is why hickory and oak give much more heat than pine.
| Species (air-dried) | Million BTU per cord |
|---|---|
| Hickory | 27.7 |
| Sugar maple | 25.5 |
| Red oak | 24.6 |
| White oak | 24.0 |
| Douglas fir | 21.4 |
| Birch | 20.8 |
| Ash | 20.0 |
| White pine | 15.9 |
These values assume seasoned wood at about 20% moisture. Green wood can lose a quarter of its heat to boiling off water.
Worked example
A face cord of red oak measures 8 ft × 4 ft with 16-inch logs and costs $100 (from $300 per full cord). The stove is 70% efficient.
- Stacked volume: 8 × 4 × 1.33 = 43 ft³, or 0.33 cord.
- Heat content: 0.33 × 24.6 = 8.2 million BTU.
- Useful heat: 8.2 × 70% = 5.7 million BTU.
- Cost per million BTU of useful heat: 300 ÷ (24.6 × 0.70) = $17.42.
- That heat equals about 49 gallons of heating oil in an 85% furnace, or 70 gallons of propane in a 90% furnace.
Stove efficiency matters
An open fireplace sends most of its heat up the chimney and may deliver only 10 to 20%. A modern EPA-certified wood stove reaches 65 to 80%, and a catalytic stove or pellet stove can do better. Doubling efficiency halves the wood you need.
Buying and storing firewood
- Buy early. Wood bought in spring has the summer to dry.
- Check moisture. A cheap moisture meter on a freshly split face should read below 20%.
- Stack it right. Off the ground, bark side up, top covered, sides open to the wind.
- Buy local. Moving firewood spreads invasive pests such as the emerald ash borer, and many states restrict it.