Propane gallons used = appliance BTU per hour × hours run ÷ 91,452 BTU per gallon, so a 100,000 BTU furnace running 6 hours burns 6.6 gallons. Enter your home's size and climate, or your appliances and their hours, to get gallons per month, then pick a tank to see when to call for a refill.
How the propane usage calculator works
A gallon of propane holds 91,452 BTU (EIA). Every appliance is a rate of burning that fuel: divide its input rating by 91,452 and you have gallons per hour.
Gallons per day = Σ (BTU per hour × hours per day) ÷ 91,452
The appliance tab does that sum for the ratings a propane supplier (Lakes Gas) lists as typical: furnace 100,000 BTU/h, water heater 40,000, gas fireplace 25,000 to 40,000 (we use 30,000), clothes dryer 20,000, grill 10,000. Your rating plate beats these, and a gas range, generator or pool heater goes in the "Other appliance" row.
Propane per month from home size and climate
The home tab estimates how much heat the house needs in a season, then how much fuel your furnace burns to make it.
Heat needed (BTU) = floor area × 0.667 BTU/h per °F per sq ft × 24 h × heating degree days
Gallons = heat needed ÷ AFUE ÷ 91,452
The 0.667 is a published rule: 800 BTU per hour per degree of temperature difference for a 1,200 sq ft house. The tight and leaky settings shift it by 25% either way, which is our adjustment. Heating degree days start at a typical value for your IECC climate zone and can be replaced with your own. A furnace at 90% AFUE burns 1 gallon of fuel for every 0.9 gallons of heat delivered.
Worked examples
- 1,200 sq ft in zone 4 (4,500 HDD), average house, 90% AFUE: 86.4 million BTU of heat, 96 million BTU of fuel, 1,050 gallons a season, 175 gallons a month over six heating months.
- 1,800 sq ft in zone 5 (6,300 HDD): 181.4 million BTU of heat, 2,204 gallons a season, 367 gallons a month.
- Appliance tab defaults (furnace 6 hours, water heater 3, fireplace 3, dryer 1): 600,000 + 120,000 + 90,000 + 20,000 = 830,000 BTU a day, 9.1 gallons a day, 276 gallons a month.
For scale, the water heater alone at 3 hours a day burns 1.3 gallons a day, about 40 gallons a month, and the dryer at one hour burns 0.22 gallons.
Tank size and when to refill
Propane tanks are filled to 80% of their water capacity so the liquid can expand with heat (Propane101). That gives the usable gallons below.
| Tank | Water capacity | Usable at 80% | Days at 9.1 gal/day, full to 30% |
|---|---|---|---|
| 120 gallon | 120 gal | 96 gal | 7 days |
| 150 gallon | 150 gal | 120 gal | 8 days |
| 250 gallon | 250 gal | 200 gal | 14 days |
| 500 gallon | 500 gal | 400 gal | 28 days |
| 1,000 gallon | 1,000 gal | 800 gal | 55 days |
The calculator subtracts your reorder level (30% by default, which is our placeholder; ask your supplier what they want) from the 80% fill, and divides the remaining gallons by your use per day. It then suggests calling about a week before that date. Use a monthly gallon figure from the height of winter, not the yearly average, because January burns far more than October.
Propane, natural gas and other fuels
One gallon of propane is 91,452 BTU, one cubic foot of natural gas is 1,036 BTU and one kWh of electricity is 3,412 BTU (EIA), which is how to compare fuels on cost per million BTU. Wood is different again: compare with the firewood calculator, which uses the same heat-loss method, and see what an electric heat pump would take in the heat pump size calculator.
Before you add an appliance
More BTU per hour means bigger gas line and regulator. Check the pipe in the gas pipe size calculator, the furnace in the furnace size calculator and a single room with the BTU calculator. For a room heater, see the space heater calculator. All are in the heating and plumbing calculators hub.
Use it as a propane consumption calculator too: the gallons per month it shows are your consumption, and the refill date follows from your tank size.