Is a Space Heater Cheaper Than Central Heat?

Compare the cost of the heat itself

To compare fuels fairly, work out what one million BTU of delivered heat costs. That cancels out the different units on each bill: kWh for electricity, therms or cubic feet for natural gas, gallons for propane.

Multiply the units by your own prices. Heat pump efficiency (COP) falls as the outdoor temperature drops, so a COP of 3 is a mild-weather figure, not a winter average for cold climates.

Reading your gas bill

US gas bills charge by the therm or by the CCF, which is 100 cubic feet of gas. One CCF holds roughly one therm of energy; the bill usually shows the exact conversion factor your utility uses. Some Canadian utilities bill in cubic meters or gigajoules, and Australian bills use megajoules (MJ). Useful conversions: one therm is about 105.5 MJ, one kWh is 3.6 MJ and one million BTU is about 1,055 MJ.

Worked example with sample prices

These prices are examples to show the method, not current rates. Use your own bills.

• Electricity at $0.15 per kWh: 293.07 × 0.15 = $43.96 per million BTU from a space heater.
• The same electricity through a heat pump at COP 3: about $14.65.
• Natural gas at $1.50 per therm in a 95 percent furnace: 10.53 × 1.50 = $15.79. In an 80 percent furnace: $18.75.
• Propane at $2.50 per gallon in a 95 percent furnace: 11.5 × 2.50 = $28.76.

With these sample prices, heat from a space heater costs nearly three times as much per BTU as heat from a gas furnace. That is common where natural gas is available, but the gap depends heavily on local prices. Homes heated by propane, heating oil or electric baseboards see a much smaller gap, or none.

When a space heater still saves money

A furnace heats the whole house. A space heater heats one room. Zone heating pays off when you can turn the central thermostat down and keep only the room you use warm.

Example: you work from a small home office 5 hours each evening and run a heater on its 1,000 W medium setting. That uses 5 kWh a day. At $0.15 per kWh it costs $0.75 a day and delivers 5 × 3,412 = 17,060 BTU of heat. If turning the central thermostat down for those 5 hours saves more than about $0.75 of gas or propane, the heater wins. In a small home in mild weather, it may not. In a large, drafty home where one person sits in one room all evening, it often does.

Run your own numbers in the space heater cost calculator, then compare with your gas bill for the same period.

When a space heater costs more

• Using several heaters in different rooms at once. You are now heating the house with the most expensive heat.
• Leaving the central thermostat where it was. The heater adds cost without cutting the furnace's.
• Running it in a room with the door open, so the heat drifts into the rest of the house.
• Heat pump homes. A heat pump in mild weather produces heat at a fraction of the cost of a resistance heater.

Tips for lower heating bills this winter

• Lower the thermostat at night and when nobody is home. A smart or programmable thermostat makes this automatic.
• Seal drafts at windows, doors and attic hatches, and add attic insulation if it is thin.
• Replace the furnace filter on schedule. A clogged filter cuts airflow and efficiency.
• Use the heater's thermostat and low setting rather than full power.

Safety

Plug space heaters directly into a wall outlet, keep them at least 3 ft (1 m) from anything that can burn, and never leave them running while you sleep or are out. Fuel-burning furnaces and heaters must be vented and serviced; put carbon monoxide alarms on every level of the home. Never use an oven, grill or outdoor propane heater to heat indoors.

Frequently asked questions