Running cost is almost entirely fuel: nameplate BTU/hr, how many hours you burn, and the therm rate on your bill. Brand and finish barely move the monthly number compared with those three inputs.
Start with BTU/hr, not square footage
Gas inserts and fireplaces are rated in BTU per hour — commonly 20,000 to 50,000 for living-room units. A 30,000 BTU/hr unit at four hours a day is a useful US planning example. Bigger glass and blowers do not change therms unless the burner itself is larger.
Hours dominate the month
Cost scales linearly with time. Two hours a night costs half of four. A weekend-only fireplace over a 30-day month is closer to eight evenings than to “always on.” Use the calculator below and copy a share link if you want a second opinion on the same inputs.
Read the therm line on the bill
Residential US therm rates often sit somewhere near $1.20–$2.00 plus a fixed customer charge this calculator ignores. If your bill shows CCF, convert with the therm factor your utility prints, then enter dollars per therm.
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
How does GasFireCost estimate fireplace running cost?+
It converts your fireplace BTU/hr into therms (natural gas) or gallons (propane), multiplies by the fuel rate you enter, then scales by hours per day, days per month, and seasonal hours. An optional efficiency derate treats the BTU figure as heat output. A standing pilot, if enabled, is extra fuel on top of the main burner.
How much does a gas fireplace cost per hour?+
With the site’s US defaults (30,000 BTU/hr, 75% efficiency assumption, $1.47/therm), a natural gas fireplace is about $0.59 per hour. The same unit on propane at $2.67/gallon is about $1.17 per hour. Your bill depends on nameplate BTU, local rates, and hours used.
What does a gas fireplace cost per month?+
At 4 hours per day for 30 days, the default natural gas example is about $71 per month, or about $140 on propane. Cut hours in half and the main-burner cost halves. A 24-hour pilot adds a smaller, steadier monthly amount.
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.
What are “season hours”?+
Season hours are the total hours you expect the main burner on across a heating season. The default is 4 hours/day × 180 days = 720 hours. Edit that field if you only use the fireplace on weekends or for a shorter winter.