Electric Tankless Water Heaters: Which One to Buy

Will your panel handle it?

Electric tankless heaters draw a lot of power at once. A 24 kW unit draws about 100 amps at 240 volts; an 11 kW unit about 46. Many older homes have a 100- or 150-amp panel, which cannot spare 100 amps. Have an electrician check before you buy.

How much hot water you really get

The DOE test rates flow at a 67°F rise (58°F in, 125°F out). In a northern winter the rise is closer to 70°F, so the biggest electric unit gives about one shower. In a warm state the incoming water is warmer and you get more. A shower is about 2 gallons a minute.

The full decode of 39 bestsellers is on best tankless water heater. For a whole house on electricity in a cold climate, a heat pump water heater is often the better answer.

Questions buyers ask

How many amps does an electric tankless water heater need?

Divide the kilowatts by 0.24 for the amps at 240 volts: an 11 kW unit draws about 46 amps, an 18 kW about 75 and a 24 kW about 100. The breakers and wire must be sized for it; an electrician will apply the code margin.

Can an electric tankless heater run a whole house?

In a warm climate with a 200-amp panel, a large one can run one or two showers. In a cold climate, the biggest certified unit here gives 0.5 GPM at the 67°F test rise, about one shower.

Is electric tankless cheaper to run than a tank?

About the same. An electric tankless heater and a standard electric tank both turn nearly all their electricity into hot water: these units are certified at UEF 0.94, and our standard tank pick, at UEF 0.93, costs about $779 a year to run. A heat pump water heater (UEF 3.75, about $193 a year) costs much less than either.