Propane vs Natural Gas Heating Calculator
| Propane $/gal ↓ · gas $/therm → | $0.80 | $1.20 | $1.60 | $2.00 |
|---|---|---|---|---|
| $1.50 per gallon | Gas | Gas | Gas | Propane |
| $2.00 per gallon | Gas | Gas | Gas | Gas |
| $2.50 per gallon | Gas | Gas | Gas | Gas |
| $3.00 per gallon | Gas | Gas | Gas | Gas |
Enter your propane price per gallon and your natural gas price per therm. The calculator converts both to dollars per million BTU of delivered heat at your furnace efficiency and names the winner, plus the exact propane price where the verdict flips.
The two fuels are not sold in comparable units, which is half the confusion: a gallon of propane carries 91,500 BTU while a therm of natural gas carries 100,000. The verdict usually favors the pipeline - gas needs no truck delivery, and EIA season data shows propane homes out-spending gas homes roughly two to one - but rural propane beats urban gas wherever the local prices line up right.
How to use
- Propane comes off the delivery ticket in dollars per gallon; natural gas comes off the utility bill in dollars per therm.
- Use one furnace efficiency for both - the same condensing furnace class serves either fuel, typically 80 or 95 percent AFUE.
- The crossover line updates live: propane only wins when its price per gallon stays under 91.5 percent of the gas price per therm.
Frequently asked questions
Is propane or natural gas cheaper to heat with?
Run the per-BTU math: propane at 2.80 dollars a gallon delivers heat at about 32 dollars per million BTU at 95 percent efficiency, while gas at 1.50 a therm delivers about 15.80. Gas wins those defaults; propane only wins when a gallon costs less than 91.5 percent of what a therm costs. The calculator draws your exact line.
Why does propane cost more per BTU than natural gas?
Supply chain: natural gas flows through a pipeline and meters continuously, while propane is liquefied, trucked to a tank on your property and billed per delivery with minimums and rent on the tank itself. Every leg of that chain shows up in the per-gallon price.
How many BTUs are in a gallon of propane versus a therm of gas?
About 91,500 in the gallon, 100,000 in the therm - so one therm of heat needs roughly 1.09 gallons of propane. That energy gap stacks on top of the price gap, which is why equal-looking price tags are never equal heat.
Can I switch from propane to natural gas?
Only if the gas main reaches your street - the pipeline is the gate, not the appliances. Most furnaces convert with a kit, but the main extension is quoted per foot and can run thousands in rural areas; the calculator tells you what annual savings would have to repay it.
Do propane and gas furnaces differ in efficiency?
No meaningful difference - the same 80 to 95 percent AFUE classes cover both, because the burner swaps but the heat exchanger physics do not. That is why the calculator can run one efficiency against both fuels and keep the comparison honest.