When a Space Heater Is Cheaper Than Raising the Whole-House Thermostat

A space heater is usually cheaper than raising the whole-house thermostat when you need to warm one occupied room for a limited time and can leave the rest of the home cooler. The savings depend on your heating system, electricity and fuel rates, insulation, room size, and how long the heater runs.

The key comparison is not the total cost of heating your house. It is the extra cost caused by raising the thermostat versus the cost of heating one room with a space heater.

Start with the space heater’s hourly cost

Most portable electric space heaters are rated at up to 1,500 watts on a standard high setting. The basic calculation is:

Cost per hour = heater wattage ÷ 1,000 × electricity rate

For example, at 1,500 watts and an electricity rate of $0.18 per kilowatt-hour:

1.5 kW × $0.18 = $0.27 per hour

A thermostat-controlled heater may not draw its full rated power continuously. Once the room reaches the set temperature, it may cycle on and off. The actual hourly average can therefore be lower, although drafts, poor insulation, and an open door can make it run more often.

Check your electric bill for the actual per-kilowatt-hour rate. If your utility uses time-of-use pricing, calculate the cost using the rate that applies when you normally use the heater.

Compare it with raising the whole-house thermostat

The cost of raising the central thermostat depends on the type of heating system.

Electric resistance heat

If your home uses electric baseboards, electric wall heaters, or another resistance-heating system, the heat is produced directly from electricity. A portable heater may reduce cost by letting you heat only the room you occupy, but the savings depend on how much central heat you avoid using.

If the central system already heats several rooms to the same temperature, a space heater does not automatically save money. The central heat may run only occasionally, especially in a well-insulated home.

Gas, propane, or oil furnaces

A fuel-burning furnace may cost less or more than a space heater per unit of delivered heat, depending on the fuel price and furnace efficiency. A portable heater can still reduce the total bill through zoning: you may be able to lower the central thermostat and heat only the room in use.

Do not compare the price of a gallon or therm directly with the price of a kilowatt-hour. Convert both systems to the cost of delivered heat, and account for the furnace’s efficiency.

Heat pumps

A space heater is not automatically cheaper than a heat pump. A heat pump can deliver more heat than the electrical energy it consumes under suitable outdoor conditions. A portable resistance heater converts electricity directly into heat, so it generally has a higher operating cost per unit of heat than an efficiently operating heat pump.

Use extra caution before replacing heat-pump heating with a space heater. A small zone-heating benefit may still exist if the central system would otherwise heat the entire home, but the savings are not guaranteed.

When a space heater is most likely to save money

A portable heater is more likely to be economical when most of these conditions apply:

• You occupy one room instead of the whole house.
• The room can be closed off from unused areas.
• You can lower the central thermostat without creating a pipe-freezing risk.
• The heater has a working thermostat and is sized for the room.
• The room is reasonably insulated and does not have severe drafts.
• You use the heater for a defined period rather than leaving it on continuously.
• Your central system would otherwise run long enough to warm multiple rooms.

The savings may be small if you only raise the thermostat by a degree for a short time. They may also disappear if the portable heater runs continuously while the central system continues maintaining nearly the same temperature throughout the home.

A practical break-even calculation

Use this process to estimate your situation:

1. Calculate the space heater’s cost per hour from its wattage and electric rate.
2. Estimate how many hours per day you would run it.
3. Estimate how much additional time the central system runs when you raise the thermostat.
4. Determine the cost of that added runtime using your fuel or electricity rate.
5. Compare the two daily totals.

For a fuel-burning furnace, the calculation requires the furnace’s input rate, efficiency, and fuel cost. For a central electric system, use its electrical demand and the number of additional hours it operates.

A plug-in energy monitor can help measure a portable heater’s electricity use, but it cannot by itself determine how much fuel or electricity the central heating system would have used. Weather, wind, sunlight, occupancy, and thermostat location can change the comparison from day to day.

Choose the right heater for the room

Wattage affects both heat output and operating cost. A 1,500-watt heater costs about twice as much per hour as a 750-watt heater at the same electricity rate when both run continuously. A higher-wattage heater is not necessarily cheaper overall if the lower-wattage model can maintain the room temperature.

Look for:

• A built-in thermostat rather than only a high/low switch
• A low heat setting for maintaining comfort at lower cost
• Tip-over and overheat protection
• A timer or scheduled operation if you only need heat at certain times
• A design appropriate for the room, such as a quiet oil-filled radiator for longer occupancy or a ceramic heater for faster spot heating

Oil-filled radiators continue releasing some stored heat after the heating element cycles off, but they do not produce free heat. Their operating cost is based on the electrical power used while the element is energized. Ceramic heaters can warm a nearby area quickly, but fan noise and airflow may matter in a bedroom or office.

Use zone heating without wasting the savings

Set the central thermostat lower before turning on the portable heater, rather than running both systems at their normal settings. Close doors to unused rooms when appropriate, but keep necessary ventilation and do not block heating-system returns or vents.

Avoid lowering the home temperature so far that pipes, pets, or vulnerable occupants are put at risk. In cold weather, maintain safe temperatures in rooms containing plumbing and follow local recommendations for preventing frozen pipes.

Keep the heater away from exterior doors, drafty windows, and high ceilings when possible. A draft can make the thermostat call for heat continuously, eliminating the expected savings. Weatherstripping and sealing obvious drafts may save more than buying a higher-wattage heater.

Electrical safety matters to the cost decision

A typical 1,500-watt space heater draws about 12.5 amps on a 120-volt circuit. That is a substantial load for a household branch circuit.

• Plug the heater directly into a properly grounded wall outlet.
• Do not use an extension cord, power strip, or plug-in adapter unless the heater manufacturer specifically permits it and the device is properly rated.
• Keep the cord and plug away from water, rugs that can trap heat, and hot surfaces.
• Stop using the heater if the plug, outlet, or cord becomes unusually hot, discolored, loose, or damaged.
• Keep combustible materials well away from the heater and follow the clearance distances in the manual.
• Do not operate a portable heater while sleeping or unattended unless the manufacturer explicitly allows that use and the installation remains safe.

If a circuit breaker trips, do not repeatedly reset it while the heater is connected. Unplug the heater, reduce the circuit load, and have a qualified electrician investigate persistent trips or signs of overheating.

When a space heater is not the better choice

A space heater may not save money when:

• You need to heat most of the home anyway.
• The room has major air leaks or poor insulation.
• You use an efficient heat pump in conditions where it is operating normally.
• The heater runs continuously at full power.
• The central system has a lower delivered-heat cost under your local fuel rates.
• The heater requires an unsafe extension cord or overloaded circuit.

If one room is consistently cold, investigate the cause instead of relying only on portable heat. Check for blocked registers, closed dampers, failed zone controls, inadequate insulation, window drafts, and thermostat placement. A heating professional can evaluate duct balance, combustion equipment, wiring, or heat-pump operation when the cause is not obvious.

Bottom line

A space heater can be the lower-cost option for heating one occupied room while the rest of the home stays cooler. Calculate its hourly cost, compare that with the added cost of central-system runtime, and consider whether your main system is a heat pump, resistance heater, furnace, or boiler. Use a thermostatic heater, reduce the central thermostat when practical, and follow the manufacturer’s electrical and clearance instructions. If the heater must run constantly to compensate for drafts or a heating-system problem, fixing the underlying issue may be the more economical solution.