Propane vs Natural Gas Cost Comparison Calculator
Compare the true annual heating cost of propane versus natural gas by accounting for fuel prices, appliance efficiency (AFUE), and your home's heat load.
Typical home: 60–120 MMBtu/year. Check your utility bills or use a Manual J estimate.
Formulas Used
Fuel Input Required (MMBtu/yr):
Fuel Input = Annual Heat Load (MMBtu) ÷ (AFUE ÷ 100)
Propane Gallons Required:
Gallons = Fuel Input (MMBtu) ÷ 0.0915 MMBtu/gallon
(Propane HHV = 91,500 BTU/gallon)
Natural Gas Therms Required:
Therms = Fuel Input (MMBtu) ÷ 0.1 MMBtu/therm
(1 therm = 100,000 BTU)
Annual Cost:
Propane Cost = Gallons × Price ($/gallon)
Natural Gas Cost = Therms × Price ($/therm)
Cost per MMBtu of Useful Heat:
= Annual Cost ÷ Annual Heat Load (MMBtu)
Assumptions & References
- Propane higher heating value (HHV): 91,500 BTU/gallon — U.S. EIA standard.
- Natural gas: 1 therm = 100,000 BTU — U.S. standard unit for residential billing.
- Propane and natural gas prices vary significantly by region and season. Check current prices from your local supplier or the U.S. EIA (eia.gov).