How Many Watts Does a Space Heater Use?

Most portable electric space heaters use 750, 1,000, or 1,500 watts, with 1,500 W being the standard maximum. That 1,500 W ceiling exists because a standard 120 V, 15-amp household circuit can safely deliver about 1,800 watts continuous, and 1,500 W (12.5 amps) leaves a safety margin. A 1,500 W heater run for 8 hours uses 12 kWh a day — about $2.04 at $0.17/kWh — which adds up fast over a winter.

Because electric resistance heating converts nearly 100% of its watts to heat, every space heater at the same wattage produces the same amount of heat and costs the same to run — an "energy-saving" ceramic heater at 1,500 W uses exactly as much electricity as any other 1,500 W heater. What differs is comfort (how the heat is delivered) and safety features. Use the calculator above to see daily cost and amperage, and the electricity cost calculator for whole-season totals.

Portable heaters almost always offer multiple wattage settings — commonly a "low" of 750 W and a "high" of 1,500 W. The table below shows typical watts, the resulting amps at 120 V, and the hourly cost at $0.17/kWh for each type and setting. Note that different technologies (ceramic, oil-filled, infrared) at the same wattage draw the same power and cost the same per hour — they differ in how evenly and quickly they warm a space, not in efficiency.

The amps column matters for safety: a 1,500 W heater draws 12.5 amps, so it should be the only significant load on its 15-amp circuit and must be plugged directly into the wall — never into a lightweight extension cord or power strip, which can overheat.

Space heaters are the simplest appliance to model because they are pure resistive loads with no duty cycle guessing on the "high" setting:

Amperage — critical for safety — is Amps = Watts ÷ Volts. On a 120 V circuit, 1,500 W ÷ 120 = 12.5 amps. A 15-amp breaker is rated for 12 amps continuous under the 80% rule, so a 1,500 W heater is right at the edge and must not share the circuit with other meaningful loads.

A common misconception is that some electric heaters are "more efficient." Every watt of electricity in a resistance heater becomes a watt of heat — they are all essentially 100% efficient at the point of use. Thermostats and timers save money not by changing efficiency but by reducing runtime: an oil-filled radiator with a good thermostat cycles off once the room is warm, so its average power over an hour drops below its rated watts even though its "on" draw is identical.

Example 1 — 1,500 W heater, 8 hours a day: Daily = 1,500 × 8 ÷ 1000 = 12 kWh. At $0.17/kWh that is $2.04 a day, about $61 a month if run every day. Annualized (if it somehow ran year-round) it would be 4,380 kWh, but you only pay for heating days.

Example 2 — 750 W heater, 6 hours: Daily = 750 × 6 ÷ 1000 = 4.5 kWh = $0.77 a day. Running a lower setting for a shorter period is dramatically cheaper — a good strategy for warming just one occupied room.

Example 3 — Heating one room vs the whole house: Suppose you drop your central heat and run a single 1,500 W heater 10 hours a day in the room you occupy: 15 kWh × $0.17 = $2.55 a day. If that lets you turn the furnace down and it saves more than $2.55 a day in furnace fuel, "zone heating" wins — but running several heaters at once quickly exceeds the cost of central heat and can overload circuits.

Space heaters are among the leading causes of home heating fires, almost always due to electrical overload or contact with combustibles. The wattage and amperage math directly informs safe use:

• One heater per circuit. A 1,500 W heater draws 12.5 amps. Adding almost anything else to a 15-amp circuit risks tripping the breaker — or worse, overheating wiring if the breaker is faulty.
• Plug directly into the wall. Extension cords and power strips are usually rated well below 12.5 amps continuous and can overheat. If you must extend reach, use a heavy 14-gauge or 12-gauge cord rated for the load.
• Give it clearance. Keep at least 3 feet from bedding, curtains, and furniture.
• Use built-in safety features. Tip-over cutoff and overheat protection are essential; a thermostat also saves energy by cycling the heater off.

If your heater lists amps instead of watts, multiply amps × 120 to get watts. To size backup power, remember a 1,500 W heater needs a full 1,500 running watts continuously — a heavy load for any generator or off-grid inverter.

1. Enter heater watts. Use the setting you actually run — 750 W low, 1,000 W medium, or 1,500 W high. The nameplate or dial shows the options.
2. Enter hours per day. Count real runtime. A thermostat-controlled heater cycles off once warm, so effective hours at full power may be less than the hours it is switched on.
3. Enter your electricity rate. Winter heating often pushes usage into higher tiers; use your marginal rate for accuracy.
4. Read the outputs. Primary shows annualized kWh; secondary shows daily kWh, daily cost, and amps at 120 V. Multiply daily cost by your number of heating days for a seasonal total.

Because every 1,500 W heater costs the same to run, savings come from using fewer watt-hours, not from a "better" heater:

• Zone heat. Heat only the room you are in and turn down the central thermostat. This is the main scenario where a space heater saves money.
• Use a thermostat and timer. Let the heater cycle off at your target temperature and shut off automatically when you leave or sleep.
• Choose the right type for the space. Infrared/radiant heaters warm people and objects directly (good for spot heating a workshop), while oil-filled radiators hold heat and warm a room evenly (good for bedrooms). Both cost the same per watt-hour.
• Run on low when possible. 750 W maintains a small warm room for half the cost of 1,500 W once it is up to temperature.
• Seal drafts. Weatherstripping and a door draft-stopper keep the heat you paid for in the room.

For a whole-winter estimate, multiply the calculator's daily cost by your heating days, or compare against your furnace using the appliance running cost calculator.

The popular claim that a space heater "saves money" is only half true, and the wattage math shows exactly when it holds. A 1,500 W heater is a genuinely large load — the same order of magnitude as a hair dryer or a microwave, but running for hours instead of minutes. Whether it saves money depends entirely on zone heating: using the heater to warm only the room you occupy while turning the central thermostat down for the rest of the house.

Here is the trade-off in numbers. Suppose you drop your central heat by several degrees and that saves your furnace, say, $3.00 worth of energy over an evening. If you then run one 1,500 W heater for 6 hours to keep your occupied room comfortable, that heater uses 1.5 × 6 = 9 kWh, or about $1.53 at $0.17/kWh. Net result: you spend $1.53 to save $3.00, a real gain of roughly $1.47 that evening. The strategy wins because you are heating a few hundred square feet instead of the whole house.

But the math flips fast when you scale up. Run three 1,500 W heaters at once — a common temptation in a cold house — and you are drawing 4,500 W, or 27 kWh over those same 6 hours, about $4.59. Now you have spent more than the $3.00 the furnace would have cost, and you have likely tripped a breaker or two, because three 1,500 W heaters need three separate 15-amp circuits. Electric resistance heat is never cheaper than an efficient central furnace or a heat pump for warming an entire home; it only wins for spot-heating a single space.

Two other factors decide the outcome. First, your central heating fuel: zone heating with electric resistance almost always beats electric baseboard or an old electric furnace, but it may not beat a modern heat pump or cheap natural gas, since those deliver heat far more efficiently per dollar. Second, how well the room holds heat: a drafty room with single-pane windows bleeds warmth as fast as the heater adds it, forcing longer runtime and erasing the savings. Seal the drafts, close the door, heat only where you are, and use one heater on a thermostat that cycles off once warm — that is the specific recipe where a space heater lowers your bill rather than raising it.

A single space heater (1,500 W) is cheaper than whole-home electric heat when you only need one warm room, but running three or four at once (4,500–6,000 W) usually costs more than a central system and can overwhelm your electrical panel. In summer, the mirror-image load is the air conditioner. Compared with an always-on refrigerator, a space heater draws about ten times the instantaneous power but runs only in cold months.

The honest way to compare any heating option is total kWh over the season. Feed the numbers into the power consumption calculator to see how a heater stacks up against your other loads, and check the dryer wattage guide for the other big resistive heat load in most homes.