Generator Wattage for an Electric Water Heater

What generator listings state about water heaters

Generator titles and bullet lists rarely name a water heater. Instead, they state two wattage figures: starting watts (sometimes called peak or surge) and running watts (sometimes called continuous). The starting figure is the higher number and covers the brief extra draw when a motor or heating element first turns on. The running figure is what the generator can supply steadily.

For an electric water heater, the heating elements are resistive loads. They do not have the large starting surge of a motor, but the total wattage of the elements still must be within the generator's starting and running ratings. The appliance nameplate lists the wattage or amperage; that figure is the one to compare with the generator's stated numbers.

The EIA explains that electricity is measured in watts, and a kilowatt is 1,000 watts. Generator listings use both terms, so a title that says "7,000 watts" and one that says "7kW" are stating the same figure. Read the title's first number as the starting figure unless the listing says otherwise.

• Starting watts: the higher figure, for brief peak draw.
• Running watts: the steady output the generator can sustain.
• Kilowatt (kW): 1,000 watts, used interchangeably in titles.

Conventional tank versus tankless electric water heaters

A conventional electric water heater with a tank uses one or two heating elements to keep a stored volume of water hot. Its wattage is relatively modest, typically in the range of 1,500 to 5,500 watts depending on the element size and the number of elements. The load is steady while the elements are on.

A tankless electric water heater heats water only when a tap is opened, but it must do so quickly. Its elements are much larger, often drawing 8,000 to 15,000 watts or more. That demand is continuous for as long as hot water flows, so the generator must hold that output, not just reach it briefly.

The listing does not tell you which type of heater you have. The nameplate on the heater does. Read the label for the wattage or the amperage and voltage; if only amperage is listed, multiply volts by amps to get watts. That calculation is a reading exercise, not a sizing promise.

Matching a listing to your heater's demand

Once you have the heater's wattage from the nameplate, compare it with the generator's starting and running figures. The heater's wattage should be at or below the generator's running watts, because the heater draws that load for the whole heating cycle. The starting figure matters less for a resistive heater, but it still must be high enough to cover the initial draw.

Generator listings in the 3,000 to 5,000 watt class are common for Florida hurricane backup. A conventional tank heater in that range may fit, but a tankless unit usually will not. The best 3000 to 5000 watt generators for hurricanes guide compares models on stated details, so you can see which listings state running watts that match your heater's label.

For a larger tankless heater, a higher-capacity portable generator may be needed. The best large portable generators for hurricanes guide covers units with higher stated output. Always read the maker's page for the generator to confirm the running watts, because the title's first figure is often the starting figure.

What this site cannot say about water heater sizing

This site does not promise that any generator will run a specific water heater, because runtime and actual draw depend on the heater's condition, the water temperature, and the generator's load. The site also does not give appliance worksheets or tables that size a home. Those calculations are best done with the appliance labels in hand and, for a permanent connection, a licensed electrician.

The Florida Division of Emergency Management advises checking and testing your generator before a storm, reading the manual, and avoiding overloading by connecting only essential appliances. That guidance is about preparation, not sizing. For wiring a generator to a home's electrical panel, a licensed electrician and the local permit office decide what is allowed.

For carbon monoxide safety, the CPSC states that portable generators must be used outside only, far from windows, doors, and vents. Follow the maker's manual and read the CPSC and Florida Division of Emergency Management pages linked below. This article gives no placement advice beyond pointing to those sources.

What to pick for your situation

The right generator for an electric water heater depends on the heater's nameplate wattage and the other loads you plan to run. If the heater is a conventional tank model and the wattage fits a mid-size portable, a 3,000 to 5,000 watt unit may be enough. If the heater is tankless or you want to run other large appliances, a larger portable or a standby unit is a better match.

For a home with a tankless electric heater, compare the heater's wattage with the generator's running watts before buying. The best large portable generators for hurricanes guide lists models with higher stated output. For a conventional tank heater, the best 3000 to 5000 watt generators for hurricanes guide is the place to start.

If you live in an apartment or condo, a portable generator may not be an option; the Florida Division of Emergency Management notes that generators may not be needed in apartments or condos and advises checking with building management. A power station could be a better fit. The best power station for apartments guide covers battery units, though a water heater's wattage is usually too high for a portable power station.

What to pick for your situation

Questions

What is the difference between starting watts and running watts on a generator listing?

Starting watts (or peak) is the brief higher draw when an appliance first turns on. Running watts (or continuous) is the steady output the generator can sustain. For an electric water heater, the running watts matter most because the heating element draws a steady load.

How do I find the wattage of my electric water heater?

Read the nameplate on the heater. It lists wattage, or volts and amps. If only volts and amps are listed, multiply them to get watts. That figure is what you compare with the generator's running watts.

Can a portable power station run an electric water heater?

Most portable power stations have a continuous AC output that is far lower than a water heater's wattage. Check the power station's stated output and the heater's nameplate. In most cases, a generator is the only practical option for a water heater.

Why does this article not give a specific wattage number for my water heater?

Water heater wattage varies by model and type. The nameplate on your unit is the only reliable source. This site does not promise that any generator will run a specific appliance, because actual draw depends on the heater and the generator's load.