Space Heater vs. Turning Up the Furnace: Which Costs Less?

A space heater may cost less than turning up the furnace if you only need to warm one room and can turn the central heat down elsewhere. If you need to heat several rooms—or have an efficient heat pump—the furnace may be the better deal. Compare your actual energy costs and the amount of space you need to heat.

Space heater versus furnace costs

A typical portable electric space heater uses resistance heat: nearly all the electricity it consumes becomes heat in the room. That does not automatically make it cheaper than a furnace, because electricity and fuel have different prices and the furnace may heat more efficiently or warm several rooms at once.

For a space heater, estimate the cost this way:

Heater power in kilowatts × hours of use × your electricity rate per kilowatt-hour = estimated cost

For example, a 1,500-watt heater running for eight hours uses 12 kilowatt-hours. Multiply 12 by the per-kWh rate on your electric bill. Actual use may be lower if its thermostat cycles the heater off and on.

To compare with a gas furnace, check the gas rate on your bill and the furnace’s efficiency rating. A furnace uses less fuel than its input rating to deliver heat to the home, and some heat is lost through the venting and duct system. A licensed HVAC professional or a utility’s energy calculator can help compare delivered heat costs if the bill’s units or equipment rating are unclear.

A heat pump changes the comparison: it can move more heat into a home per unit of electricity than a resistance heater produces. In many cases, raising the heat-pump thermostat is cheaper than running a plug-in heater. Check your system’s guidance, especially in cold weather or if it uses auxiliary resistance heat.

When a space heater is likely to cost less

A space heater is most likely to save money when you’re using one room, can lower the central thermostat without making other rooms uncomfortable or risking frozen pipes, and don’t need the heater to run continuously. It can also make sense for a short period while the rest of the home stays at a lower temperature.

Savings are less likely if the heater runs for many hours, the room is drafty, or the central system has to work harder to recover the temperature afterward. A heater warms the area around it; it does not make the rest of the home comfortable or protect plumbing in cold areas.

When turning up the furnace makes more sense

Use the central system when several rooms need heat, when household members are in different areas, or when keeping the whole home above a safe minimum temperature matters. A furnace can be more practical than running multiple space heaters, which add electrical load and require safe placement and supervision.

If you have a heat pump, avoid assuming that a space heater is the cheaper option. Consult the heat-pump manufacturer’s instructions or your HVAC contractor about thermostat settings and auxiliary heat. Frequent large thermostat changes can cause some systems to use backup heat.

Compare your options for your home

1. Check your energy rates. Use the rates on your current utility bills, not a national average.
2. Estimate heater use. Multiply the heater’s wattage by expected hours, then divide by 1,000 to get kilowatt-hours. Multiply by your electricity rate.
3. Identify your heating system. Gas, electric resistance, and heat-pump systems have different operating costs. Look up the furnace’s efficiency or ask an HVAC professional if you cannot find it.
4. Consider the area being heated. One occupied room favors targeted heating; multiple rooms usually favor central heat.
5. Factor in comfort and safety. Don’t lower the central heat so far that pipes could freeze, and don’t leave a portable heater unattended or operating while you sleep unless its instructions explicitly allow that use.

Use a space heater safely

Place the heater on a stable, level surface and keep it away from bedding, curtains, furniture, and other combustibles. Plug it directly into a wall outlet unless the manufacturer says otherwise; avoid extension cords and power strips. Keep it out of walkways, follow its manual, and stop using it if the plug, outlet, or cord becomes hot or damaged. If a circuit trips repeatedly, unplug the heater and have the cause checked rather than resetting the breaker over and over.