How Long Does a Cord of Wood Last? Calculator for Your Stove
How long a cord lasts depends on how much heat the wood holds and how much heat you ask of it. No single number fits every home. This calculator uses your own stove figures, so the answer is for your setup.
The formula
days = cords × million BTU per cord × 1,000,000 × stove efficiency ÷ (BTU per hour × hours per day)
- Million BTU per cord comes from the BTU chart, based on Utah State University Extension data for 44 species.
- Stove efficiency is the share of the wood's heat that reaches the room instead of going up the flue.
- BTU per hour is the heat you expect the stove to deliver while it is burning. Take it from your stove's manual, not from this page. Which number to use depends on how hard you run the stove.
- Hours per day is how long the stove runs at that output.
The calculator leaves the stove output and the hours blank on purpose. They differ a lot from one home to the next, and this site has no source for a typical value.
Worked example
These inputs are made up to show the math. They are not typical for any home. One cord, a 70% efficient stove that puts out 20,000 BTU per hour, burned 8 hours a day (160,000 BTU per day):
| Wood | Million BTU per cord | Useful heat at 70% | Days at 8 hours | Days at 12 hours |
|---|---|---|---|---|
| Oak, White | 29.1 | 20.37 million BTU | 127 | 85 |
| Oak, Red | 24.6 | 17.22 million BTU | 108 | 72 |
| Pine, White | 15.9 | 11.13 million BTU | 70 | 46 |
| Cottonwood | 15.8 | 11.06 million BTU | 69 | 46 |
Check one row: red oak, 24.6 × 1,000,000 × 0.70 = 17,220,000 BTU. Divide by 20,000 × 8 = 160,000 BTU per day and you get 107.6 days.
What changes the answer
- Species. A cord of white oak lasts about 1.8 times as long as a cord of white pine in the example (29.1 ÷ 15.9), because it holds that much more heat.
- Hours or output. Doubling the heat per day halves the days. At 30,000 BTU per hour for 8 hours, one cord of red oak lasts 72 days instead of 108.
- Moisture. The USU heat values assume dry wood, and the U.S. Department of Energy gives 20% moisture or less as the standard. Wet wood gives less heat. See the seasoning guide.
- How much wood you need for a season. Work backward from last winter's fuel bill with how much firewood do I need.
Sources
- Utah State University Extension, Wood Heating, Table 1: million BTU per cord by species.
- U.S. Department of Energy, Wood and Pellet Heating: stove efficiency range of 65–75% for improved non-catalytic stoves; 20% moisture standard.