What size space heater for a bedroom

For a typical bedroom, start with about 10 watts per square foot: a 150-square-foot room would need roughly 1,500 watts for supplemental heat. Treat that as a starting estimate, not a guarantee—a drafty or poorly insulated room may need more heat, while a well-insulated room may need less. Check the heater’s manual and use it only as directed, especially in a bedroom where people may be sleeping.

Estimate the bedroom size

Multiply the room’s length by its width to get square footage, then multiply by about 10 watts:

Room area in square feet × 10 = estimated heater wattage

Many portable heaters top out at 1,500 watts on a standard household outlet. If your estimate is higher, that does not mean you should plug multiple heaters into the same outlet or circuit. Consider improving insulation or using the home’s primary heating system instead. Have an electrician assess the circuit if you are unsure what it can safely support.

Adjust for your room and climate

The 10-watt estimate assumes an ordinary ceiling height and reasonably typical insulation. You may need more heating capacity if the bedroom has high ceilings, drafty windows, poor insulation, or very cold outdoor temperatures. A smaller, enclosed, well-insulated bedroom may warm more easily.

A heater’s wattage describes its electrical input, not how evenly it will warm the room. Placement, airflow, thermostat behavior, and heat loss all affect comfort. A thermostat can help maintain a steadier temperature, but it does not make an undersized heater more powerful.

Choose a heater that fits how you use the bedroom

For quick, directed warmth while you are in the room, a ceramic heater with adjustable heat settings and a thermostat may be convenient. An oil-filled radiator warms more gradually and provides steady radiant heat, but it can take longer to feel warm. In either case, compare the heater’s maximum wattage with your estimate and check that its safety features and instructions suit your intended use.

Do not assume a portable heater is safe to run while you sleep or leave unattended. Follow the manufacturer’s instructions. Keep the heater on a stable, level surface and at least 3 feet from bedding, curtains, clothing, and other combustible materials. Plug it directly into a wall outlet—not an extension cord or power strip—and avoid sharing the circuit with other high-wattage appliances.

Check the outlet and circuit

At 120 volts, a 1,500-watt heater draws about 12.5 amps, so it can use much of the capacity of a typical household circuit. Avoid operating another high-power appliance on the same circuit at the same time. If a breaker trips, stop using the heater on that circuit; do not repeatedly reset the breaker or use a larger fuse. Ask a qualified electrician if you cannot identify a suitable circuit.

For a bedroom around 150 square feet or smaller, a 1,500-watt heater is a common maximum-size choice for supplemental heat. For a larger, drafty, or unusually cold room, address heat loss or use the home’s central heating rather than trying to solve the problem by stacking portable heaters.