Space Heater Running Costs: Calculate Energy Use From Wattage

The running-cost formula is simple: watts divided by 1,000, multiplied by hours, multiplied by your electricity price. The hard part is choosing the correct watts and realistic runtime. A 1,500-watt heater draws 1.5 kW while its heating element is on; a thermostat may cycle it, and a low setting may draw less. Read the label or manual instead of assuming every “small” heater has the same load.

Lasko’s CD08500 product page lists a $54.99 product price at the time checked, 900–1,500 watts of output, 120 volts, indoor use, overheat protection, and a three-year limited warranty. See the manufacturer page. The price is for that named product and excludes tax, shipping, and installation; it is not a national heater price.

Fill out the cost card

Record model, selected setting, watts, hours per day, days per month, thermostat duty cycle, utility rate, and any time-of-use period. Then calculate:

monthly kWh = (watts ÷ 1,000) × hours/day × days × duty cycle

monthly cost = monthly kWh × all-in electricity rate

Use the variable rate that applies to the hours, including delivery and riders if you are estimating the bill impact. A utility’s advertised supply rate may not be the all-in rate. EIA explains that delivered retail prices include generation, transmission, distribution, taxes, and fees, and that rates can apply to individual services. Its electricity-rate FAQ is a useful check on that distinction.

Three labeled runtime scenarios

Assume a 1,500-watt setting, 6 hours per day, 30 days, and an all-in rate of $0.20/kWh. At 100% on-time, use is 1.5 × 6 × 30 = 270 kWh, costing $54. At a hypothetical 60% duty cycle, use is 270 × 0.60 = 162 kWh, costing $32.40. At a 900-watt low setting for the same schedule and a 60% duty cycle, use is 0.9 × 6 × 30 × 0.60 = 97.2 kWh, costing $19.44. They are assumptions, not a forecast of a particular room or utility bill.

The fixed customer charge does not rise because you plugged in one heater, but added kWh can push a tiered or time-of-use rate into a higher block. Compare the heater’s incremental kWh with the bill’s current usage tier. If the heater runs during a peak window, use the peak rate in the worksheet.

Purchase scope and safe use

Separate product price from operating cost. A portable unit usually needs no installation invoice, but a permanently wired heater, new circuit, or thermostat is an electrical job that belongs in a qualified electrician’s quote. Do not use extension cords, modify wiring, or place the heater near water or blocked airflow. Follow the manufacturer’s indoor-use, clearance, and overheat instructions.

Use a plug-in energy meter only if the device and meter are rated for the load and the measurement can be made safely. Otherwise use the nameplate and utility data. Check whether the heater replaces another heat source; the relevant decision is the added household cost, not the heater’s cost alone. After a week, compare actual runtime and kWh with your worksheet and revise the duty cycle. The resulting estimate will be more useful than a generic “per hour” number.