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Electrical

Can an electric tankless water heater run a whole house?

In a mild climate with one or two fixtures at once, often yes; in a cold climate it struggles, and it draws 112 to 150 amps in the sizes that come close.

By Tanklessly Editorial · Updated October 2026

The short answer

Flow is power divided by rise. A 27 kW unit holds about 4.1 GPM at a 45°F rise but 2.6 GPM at a 70°F rise; a 36 kW unit 5.5 and 3.5. At 2 GPM a shower that is two showers in a mild climate and one to one and a half in a cold one. Those units draw about 112 and 150 amps at 240 volts.

By climate

Whole-house electric flow (estimates)
Unit	45°F rise	70°F rise	Amps at 240 V
18 kW	2.7 GPM	1.8 GPM	75 A
24 kW	3.6 GPM	2.3 GPM	100 A
27 kW	4.1 GPM	2.6 GPM	112 A
36 kW	5.5 GPM	3.5 GPM	150 A

Units in the catalog

Atmor AT-36N-XTP 36 kW Electric Tankless Water Heater, Eemax EEM24036 36 kW Electric Tankless Water Heater and Eemax HA036240 36 kW Electric Tankless Water Heater.

Products mentioned

Whole-house electric tankless · Atmor

Atmor AT-36N-XTP 36 kW Electric Tankless Water Heater

36 kW

Whole-house electric tankless · Eemax

Eemax EEM24036 36 kW Electric Tankless Water Heater

36 kW · 240 V

Whole-house electric tankless · Eemax

Eemax HA036240 36 kW Electric Tankless Water Heater

36 kW · 240 V · 8.0 GPM max

Questions readers ask

What size electric tankless for a whole house?

Usually 24 to 36 kW, and only where the winter inlet water is mild enough. Check flow at your winter rise and the amps against your service.