Same BTU rating, two meters. Natural gas is usually cheaper per hour in the US when a main exists. Propane wins on availability, not on fuel price per BTU at these defaults.
Default scenario
Natural gas versus propane fireplace running cost at default 30,000 BTU/hr settings
Metric
Natural gas
Propane
Default rate
$1.47 / therm
$2.67 / gallon
Energy unit
100,000 BTU / therm
91,500 BTU / gallon
Cost per hour
$0.59
$1.17
Cost per day (4 h)
$2.35
$4.67
Cost per month
$70.56
$140.07
Cost per season (720 h)
$423.36
$840.39
Default rate
Natural gas
$1.47 / therm
Propane
$2.67 / gallon
Energy unit
Natural gas
100,000 BTU / therm
Propane
91,500 BTU / gallon
Cost per hour
Natural gas
$0.59
Propane
$1.17
Cost per day (4 h)
Natural gas
$2.35
Propane
$4.67
Cost per month
Natural gas
$70.56
Propane
$140.07
Cost per season (720 h)
Natural gas
$423.36
Propane
$840.39
Same 30,000 BTU/hr fireplace, 75% efficiency assumption, 4 hours/day, 30-day month, 720 season hours, no pilot. Rates are US planning defaults, not your tariff.
What this comparison leaves out
Utility customer charges, propane tank rental, delivery minimums, taxes, and conversion-kit hardware are not in the table. Those can erase a fuel-price gap over a short season. The calculator is for burner-hour math only.
How to use your own rates
Open the calculator, switch fuel, tap Edit rate, and paste the number from your bill or ticket. Copy the share link so both fuels can be compared with identical hours. Methodology and conversions live on the methodology page.
Compare with your rates
4 h
30 days
US default $1.47/therm. Using default.
Default 720 hours (hours/day × 180 days).
Per hour
$0.59
Main burner
Per day
$2.35
4 h on
Per month
$70.56
Per season
$423.36
720 h
Fuel use: 0.4 therms/hour of burner time (40,000 BTU/hr after assumptions).
GasFireCost is unofficial. It estimates fuel cost from BTU ratings and the rates you enter. It does not include taxes, utility customer charges, tank rental, or installation. No affiliation with OEMs or utilities. Verify rates with your utility or propane supplier. See methodology.
Month
$70.56
Season
$423.36
Frequently asked questions
Is natural gas cheaper than propane for a fireplace?+
Usually, on a per-BTU basis, yes — at these US defaults natural gas is about half the hourly cost of propane for the same fireplace. Propane can still be the practical fuel where there is no gas main. Compare with your actual $/therm and $/gallon, not national averages.
Is a therm the same as a CCF on my gas bill?+
Not always. A therm is 100,000 BTU. A CCF is 100 cubic feet of gas, which is close to one therm but the exact heat content varies by utility. If your bill is in CCF or MCF, convert using the therm factor printed on the bill, then enter $/therm in the calculator.
How many BTU are in a gallon of propane?+
This calculator uses 91,500 BTU per gallon as a round US planning number. The US Energy Information Administration’s HD-5 propane conversion is 91,452 BTU per gallon (higher heating value). The difference is under 0.1% and does not change a household estimate in a meaningful way.
Why is efficiency set to 75% by default?+
Many vented gas fireplaces deliver roughly 70–80% of nameplate heat to the room; the rest leaves with exhaust. The derate is an assumption, not a lab rating. If your BTU/hr is already the input (fuel) rating, turn the derate off so cost tracks fuel burned, not heat delivered.