Best overall
Westinghouse iGen4500
4,500W start · 3,700W run
Gasoline · Inverter · 52 dBA · remote start · RV-ready TT-30R
Quiet enough for a campground and strong enough to start a 30-amp RV air conditioner.
Find on AmazonWhat size generator to run a electric water heater (tank)?
Short answer
A electric water heater (tank) draws about 4,000 watts and has no motor surge, so a generator rated for at least 4,000 watts can run one on its own — a 4,000W unit gives comfortable headroom for anything else you add.
Running watts
4,000W
Starting watts
4,000W
Minimum generator
4,000W
Recommended
4,000W
Sizing a generator for a electric water heater (tank)
A electric water heater (tank) is a resistive load with no motor, so its starting and running watts are the same — about 4,000 watts. You only need to cover that steady draw, plus headroom for anything else on the generator.
To run one on its own, choose a generator rated for at least 4,000 starting watts. To run it alongside other essentials, add up everything you need and size up — the calculator below does that math for your exact list.
Run your full appliance list
This page covers the electric water heater (tank) on its own. Open the calculator with it pre-selected, then add everything else you plan to power at the same time.
Size a generator with a electric water heater (tank)Recommended midsize portable generators
Real, widely available units in the 3,500 – 8,500W class. Independent picks — we're not affiliated with any manufacturer or retailer and earn nothing from these links.
Best value
Westinghouse WGen7500
9,500W start · 7,500W run
Gasoline · Remote start · transfer-switch ready (L14-30R)
Serious home-backup wattage — enough for essentials circuits via a transfer switch — at a midsize price.
Find on AmazonQuietest
Champion 6250W Open Frame Inverter (100519)
6,250W start · 5,000W run
Gasoline · Open-frame inverter · 69 dBA · <3% THD
50% quieter and 20% lighter than a conventional 5,000W unit, with inverter-clean output.
Find on AmazonFrequently asked questions
What size generator do I need to run a electric water heater (tank)?
To run a electric water heater (tank) on its own you need a generator rated for at least 4,000 starting watts. We recommend a 4,000W (midsize portable) unit so you have headroom to add other appliances without running the generator at its limit.
How many watts does a electric water heater (tank) use?
A electric water heater (tank) uses about 4,000 watts. It has no motor, so its starting and running watts are the same. Always check your unit's nameplate for exact figures.