What Size Inverter to Run a Space Heater?

Answer
2,000 W pure sine · 1,500 W surge

A typical space heater draws about 1,500 W. Size the inverter for at least 2,000 W continuous. At 12 V it pulls about 139 A from the battery.

Free, no sign-upInstant resultsUpdated October 2026
W
Everything on at the same time.
W
Largest motor only: fridge ≈ 1,000–2,000 W.
%
Inverter size
–
How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

    More questions like this

    RefrigeratorMicrowaveCoffee MakerWindow Air ConditionerTVCPAP MachineSump PumpAll quick answers

    Why this size

    Most space heaters draw 1,500 W on high. We size the continuous rating at 125% of running watts and check that the surge rating (usually about twice the continuous rating) covers the startup.

    Value
    Running watts1,500 W
    Surge needed1,500 W
    Battery current at 12 V139 A
    Battery current at 24 V69 A

    Frequently asked questions

    How long will a 100Ah battery run a space heater?

    About 0.6 hours from a 12 V 100 Ah lithium battery at a steady 1,500 W (less for cycling appliances, more for intermittent ones).

    Do I need a pure sine wave inverter?

    Yes for motors, compressors, medical devices and modern electronics.

    Open the full calculator: Inverter Size Calculator →