Cost per Hour
| Fireplace input | Natural gas ($1.70/therm) | Propane ($2.50/gal) |
|---|---|---|
| 20,000 BTU/hr | $0.34 | $0.55 |
| 30,000 BTU/hr | $0.51 | $0.82 |
| 40,000 BTU/hr | $0.68 | $1.09 |
Cost per hour on high. Many fireplaces have a flame adjustment, and running on low cuts both the cost and the heat. Four hours a night on a 30,000 BTU natural gas fireplace is about $61 a month; on propane, about $98.
Per Unit of Heat, the Furnace Usually Wins
Of the gas a fireplace burns, the share that ends up heating your home is its fireplace efficiency (FE). Canada has required at least 50% for heating fireplaces made since 2020, and the EnerGuide label shows each model's rating; Natural Resources Canada notes some models are more than twice as efficient as others. A typical direct-vent fireplace lands around 65%, while a new furnace delivers 95% of its fuel as heat. Heat from that fireplace costs about 46% more than the same heat from a 95% furnace on the same fuel.
| Source | Cost per 100,000 BTU of heat (natural gas) |
|---|---|
| Fireplace, 50% | $3.40 |
| Fireplace, 65% | $2.62 |
| Fireplace, 80% | $2.13 |
| Furnace, 80% AFUE | $2.13 |
| Furnace, 95% AFUE | $1.79 |
| Vent-free fireplace (~99%) | $1.72 |
Vent-free fireplaces put nearly all their heat into the room, but they also put all their combustion products and water vapor there. They're limited in some states and cities, including California, and should never be the only heat in a tight, poorly ventilated house.
When Zone Heating Pays Off
The saving comes from turning the rest of the house down, not from the fireplace itself. With the thermostat 4°F lower for 4 hours a night, the furnace saves about 2% of the heating bill, $3 a month on a $150 bill. That rarely covers the extra cost of a 65% fireplace. The fireplace comes out ahead when:
- Your main heat is electric baseboard or an electric furnace. Gas heat is far cheaper than resistance heat in most of the U.S.
- The fireplace is vent-free or a high-efficiency insert and you heat one room for long stretches.
- You turn the whole house down a lot, for example closing off most rooms and living in one for the evening.
Against a modern heat pump, a gas fireplace almost never saves money, except in very cold weather when the heat pump is leaning on its backup strips. See aux heat vs emergency heat for that case.
The Pilot Light Adds Up
A standing pilot burns around the clock whether the fireplace is on or not. Estimates vary widely: figures collected by BuildItSolar run from about 5 to 12 therms a month per pilot, while a Wisconsin utility calculator uses 2.6. At about 800 BTU an hour, a pilot uses roughly 5.8 therms a month, about $10 on natural gas or $16 on propane. Through the heating season, part of that heat warms the house. Over five warm months it's about $50 of gas, or $80 of propane, with nothing to show for it.
Canada now requires new fireplaces to shut off the pilot automatically, or limit a continuous pilot to seven days. In the U.S., many newer models use electronic ignition. If yours has a standing pilot, turning it off for the summer is one of the easiest savings in the house; follow the relight steps in the manual, and have it checked if it's hard to relight.
Comfort and Backup Heat
The real case for a gas fireplace is often comfort and resilience, not cost. A fireplace with a standing pilot or battery backup can still heat a room during a power outage, when the furnace blower can't run. If that's the reason you have one, the pilot cost is the price of that insurance. For outage planning, see how fast a house cools without power.