How much propane does a furnace use per day?
While the burner is on, a furnace burns propane at a steady rate: its input rating in Btu per hour divided by the 91,452 Btu in a gallon. An 80,000 Btu furnace burns 0.88 gal an hour at full fire. A day's use depends on how many of the 24 hours it runs, and that follows the weather. Enter your furnace below to get both numbers.
- 250 gal tank13 days
- 500 gal tank26 days
- 1,000 gal tank53 days
The run time assumes your furnace just keeps up on a 0 °F day. A furnace bigger than the house needs runs less than this, and then the real gallons are lower. Two gauge readings tell you the real number (see below).
Gallons per day by outdoor temperature
Your furnace (80,000 Btu/h input, sized for 0 °F) through the season. The tank columns are whole days from the 80% fill line down to 20%, which is 150, 300 and 600 gal of propane.
| Outdoor | Burner on | Gal/day | 250 gal tank | 500 gal tank | 1,000 gal tank |
|---|---|---|---|---|---|
| 50 °F | 23% | 4.9 | 30 days | 61 days | 122 days |
| 40 °F | 39% | 8.1 | 18 days | 37 days | 74 days |
| 30 °F | 54% | 11.3 | 13 days | 26 days | 53 days |
| 20 °F | 69% | 14.5 | 10 days | 20 days | 41 days |
| 10 °F | 85% | 17.8 | 8 days | 16 days | 33 days |
| 0 °F | 100% | 21.0 | 7 days | 14 days | 28 days |
| -10 °F | 100% | 21.0 | 7 days | 14 days | 28 days |
A run time of 100% means the furnace can't keep up and the house cools. Below the temperature it is sized for, that is what happens, so the gallons stop rising there.
Propane furnace gallons per hour by size
By input rating. Running nonstop is the most a furnace can burn in a day; the last column is half the day.
| Input rating | Gal/hour | Gal/day nonstop | Gal/day at 50% |
|---|---|---|---|
| 40,000 Btu/h | 0.44 | 10.5 | 5.2 |
| 60,000 Btu/h | 0.66 | 15.7 | 7.9 |
| 80,000 Btu/h | 0.88 | 21.0 | 10.5 |
| 100,000 Btu/h | 1.09 | 26.2 | 13.1 |
| 120,000 Btu/h | 1.31 | 31.5 | 15.7 |
The math
gal per hour = input Btu/h ÷ 91,452
input Btu/h = output Btu/h ÷ AFUE
burner on = (65 − outdoor °F) ÷ (65 − sizing °F)
gal per day = gal per hour × 24 × burner on
- A gallon of propane holds 91,452 Btu (EIA).
- AFUE is the percentage of the fuel's heat that becomes space heat instead of being lost (ENERGY STAR furnace criteria).
- The run-time line is the degree-day idea that EIA uses with a 65 °F base (EIA, degree days): the heat a house needs grows with how far the day's average falls below 65. Worked example with the default furnace, 80,000 Btu/h sized for 0 °F: at 30 °F it runs (65 − 30) ÷ (65 − 0) = 53.8% of the day, so 0.875 × 24 × 0.538 = 11.3 gal.
- On those terms your furnace burns 0.323 gal per degree day. Gallons used between two of your own readings, divided by the degree days in between (the method on the heating oil use page), give your real figure. A lower one means the furnace is bigger than the house needs.
Check it against your tank
The estimate above is a starting point. Read the tank gauge on two dates a week or more apart and enter both in the propane tank calculator. It turns the percents into gallons and gives your real use per day. Divide that by the gallons per hour above and you have the hours your furnace runs.
What this leaves out
- A two-stage or modulating furnace can run on low fire, below its rated input. While it does, it burns less per hour than the table shows.
- A propane water heater, range or dryer on the same tank adds to the daily use, all year.
- Sun, wind and a setback thermostat move the run time from day to day. The temperature bands are daily averages.
Related
- 500 gallon propane tank chart: gauge percent to gallons, and days left at your use.
- Heating fuel cost comparison: propane against oil, gas, a heat pump and wood, per million Btu.
- Heating oil use per day: the same weather question for an oil boiler.