Battery backup for a space heater: do not do this, and here is what to do instead

This is the page for the search everyone makes on the first cold night of an outage, and the answer is the same for every power station on the market: no. Not because the units are weak, but because a resistance heater is the single most energy-hungry thing in a house, and the runtime table above is the whole argument. The rest of this page is what to do instead, sized in the same watt-hours.

The arithmetic, from the heater’s own label

Lasko’s 754200, one of the most common ceramic heaters sold, is rated 12.5 A at 120 V: 1,500 W on high, 900 W on low. A heater has no start-up surge and no duty cycle unless a thermostat gives it one; it draws its rating every second it runs. A 2 kWh power station holds about 1,740 Wh at the outlet after the inverter’s roughly 15% loss, as the usable capacity guide explains, and 1,740 divided by 1,500 is 1.16 hours. On the low setting, just under two. A thermostat cycling the heater half the time doubles that again, to a few hours of one room barely holding temperature. Then the battery is empty, and the refrigerator, the phones and the CPAP go with it.

Why bigger does not fix it

An 8-hour night on high is 12,000 Wh at the outlet, roughly 14 kWh of usable battery. That is the whole-home class with several expansion batteries, a system sized to run a house for days, spent on one heater in one room. Even then it heats the room about as well as leaving the oven door open, because resistance heat converts every watt-hour to warmth at the same one-to-one ratio no matter how much you paid for the battery. There is no efficient electric space heater; the efficient path is not heating air.

What a battery is good for on a cold night

Warm the person, not the room. A queen electric blanket is rated around 180 W at full, and most run lower once warm, so a 1 kWh unit carries one for most of a night and a 2 kWh unit carries two, with the refrigerator still running alongside. A heated mattress pad draws about the same. Layers, a closed door on the smallest bedroom, and towels along the gap under it do the rest; a house holds its heat for a day or more if the doors stay shut. The winter storm plan puts these in order with the food and medical windows, and the refrigerator page shows what the battery you were about to plug a heater into can actually protect.

If the house has a furnace

A gas furnace’s blower and controls are a modest electrical load compared with a space heater, and they heat the whole house. Running them from a battery means a transfer switch installed by a licensed electrician, which is the one heating project on this site worth a battery, and the one that is not a do-it-yourself job.

Combustion heat, once, plainly

Propane heaters that the maker rates for indoor use, with an oxygen depletion sensor, exist and are widely used in outages. Run one only as its manual says, with a window cracked and a battery CO alarm in the room. Anything not rated for indoor use, every charcoal grill and every gas generator, stays outside and away from openings. Winter storms are when carbon monoxide deaths spike, because the heat source comes indoors out of the snow.