What Size Generator Do I Need to Run an Electric Water Heater?

The element is a resistive load, so the chart shows no extra surge on top of the running watts.

Quick answer: Honda lists a hot water heater at 4,500 running watts and 4,500 starting watts at 240 V, and Champion lists an electric water heater at 3,000–4,500 watts with no separate start. Plan on 240 V output and a generator whose running and starting ratings both clear 4,500 W. The Champion manual lists 5,000 W running and 6,250 W starting at 120/240 V, which covers that element, while two EU2200i units in parallel reach only up to 4,400 W.

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Running and starting watts

Load	Running watts	Starting watts	Source
Hot water heater (240 V)	4,500	4,500	Honda
Electric water heater	3,000–4,500	Not listed	Champion

Honda's wattage guide lists starting watts, then running watts. Champion's chart lists running watts, then starting watts. This table puts every figure in the Running and Starting columns. Not listed means that source does not give a separate starting figure.

How to size it

Add the running watts of every load that will be on together, then add the single highest starting surge (Generac; Honda). Generac notes that starting watts are often 2–3 times running watts, and that standby units should get a dealer survey.

Because Champion lists no extra start, do not invent one. The tank can be heated in a shift: run the element while other large motors are off, then switch back. Switching a hardwired 240 V circuit needs a transfer switch or interlock installed by an electrician. See the transfer switch sizing guide.

Check a full load list on the generator size calculator.

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Run the generator outdoors only, 20 ft from the house (CPSC).

FAQ

Does a water heater have a starting surge?

Not on these charts. Honda lists 4,500 W for both running and starting. Champion lists 3,000–4,500 W and no separate start.

Can two EU2200i units run a 4,500 W element?

Parallel output is up to 4,400 W, which is under 4,500 W.

Which published generator rating covers 4,500 W?

The Champion manual lists 5,000 W running, 6,250 W starting, and 120/240 V output.

Can a gas water heater use this chart?

This page is the electric element. Honda's row is a 4,500 W hot water heater at 240 V. A gas tank is not given a watt row here.