What Size Power Station to Run a Space Heater?

Heat is the one thing batteries are genuinely bad at, and the reason is arithmetic rather than engineering. A space heater converts electricity into warmth at essentially 100% efficiency, which sounds good until you notice what that means: every watt of heat you feel is a watt drawn from the battery, continuously, with no duty cycle to hide behind.

Compare that with a refrigerator, which is the other big household load. A fridge's compressor runs 30-50% of the time, so a 150W fridge costs you roughly 1,260Wh across a day. A 1,500W heater running continuously costs you 1,500Wh in a single hour. How many watt-hours does a refrigerator use makes the duty-cycle point properly, and the contrast is the whole story here.

The arithmetic, with your own numbers

Read the plate on your own heater before you use any of the figures above. Space heaters are commonly sold at 1,500W high and 750W low on a 120V circuit, but ceramic, oil-filled, panel and fan heaters all differ, and a thermostat changes everything — see below.

The output ceiling comes first

Before runtime, check whether the unit will run the heater at all. A 1,500W load needs a published continuous rating above 1,500W with margin, because a heater is a sustained load rather than a brief one and running an inverter at 100% of its rating for an hour is not a plan.

Every unit under 1kWh is out on output alone — a 300W or 600W inverter will not start a 1,500W heater, and nothing about the capacity changes that. What can a 1000W power station run sets out where those ceilings land across the whole load list.

What a thermostat changes, and what it does not

A heater on a thermostat in a small, well-insulated room cycles, and cycling cuts consumption in exactly the way a fridge's duty cycle does. In a closed bedroom a 1,500W heater might run 40% of the time once the room is up to temperature, which turns 1,500Wh an hour into roughly 600Wh an hour and makes a 2kWh unit a two-to-three-hour proposition rather than a one-hour one.

What it does not change is the startup period or a draughty space. Bringing a cold room up to temperature is full-power running, and a tent, a van with a vent open, or a garage will never reach a setpoint at all — which means the heater runs flat out until the battery is empty. That is the case where the arithmetic above applies exactly as written.

What to do instead

• Heat with fuel, power with battery. This is the right answer in a van, a tent or an ice shelter. A diesel air heater burns fuel for heat and uses only a few watts of electricity for its fan and pump — best power station for a diesel heater shows how small that load really is, and it is the most useful page on the site for this problem.
• Heat the person, not the room. A 12V electric blanket at 40-60W is 25 to 35 times less demanding than a space heater, and it keeps you warm rather than the air around you. What size power station for an electric blanket runs those numbers.
• Use a heated vest, socks or a hot water bottle. None of these draw anything meaningful, and in a cold outage they are what actually works.
• Shrink the space. A closed bedroom with a door shut reaches a setpoint; a whole floor does not.
• If a heater really is mandatory, use a generator outdoors and extension cords in. Portable power station vs gas generator sets out that trade honestly — a generator wins on exactly this load.

Cold weather makes it worse

The situation in which you want a heater is also the situation in which the battery delivers less than its rating. Cold raises a lithium cell's internal resistance and shrinks the usable watt-hours, so a battery sitting in a 30F garage gives up noticeably less than the same battery at room temperature — and the heater's demand does not shrink to match. Power stations in cold weather covers the derate and the charging rules, which matter more than any sizing table here.

If you still want the biggest option

The honest top of the range is the Anker SOLIX F3800 at 3,840Wh with 6,000W continuous, expandable to 53.8kWh across six packs — and at six packs you are no longer shopping for a portable power station, you are shopping for a home battery system. Best power station for hurricane season and what size power station for a power outage cover that decision properly.

For an apartment, where a generator is not an option at all, the practical answer is to accept that heat is off the table and size for the fridge, the router and the lights instead. Best power station for an apartment sets out that priority list.