How Many Amps Does A Tankless Water Heater Use? (42-167 Amps)

Electric tankless heaters use exclusively electricity to heat up water. As we know, heating up water is a very demanding task. That’s why electric tankless water heaters require a strong electricity current; ie. amps. How many amps do tankless water heaters use?

Tankless heaters can draw anywhere from 42 amps to 167 amps.

We can calculate exactly how many amps does a tankless water heater because we know two key factors:

1. Overall power or wattage. Electric tankless water heaters can have a power input from 10,000W (10 kW) to 40,000W (40 kW).
2. Voltage. To reduce the amp draw, all electric tankless water heaters operate on a 240-volt circuit.

Using the electric power equation (P = I×V), we can calculate the by expressing the I or electric current like this:

I (amps) = P (watts) / V (volts)

Example: Let’s say we have a 30 kW tankless water heater on a 240-volt circuit. How many amps does a 30 kW tankless water heater use? We use the electrical power equation in this way:

I (amps) = 30,000W / 240V = 125 amps

Such a heater draws 125 amps (you need several 20-amp or 30-amp breakers for installation).

We have calculated amp draws for tankless water heaters ranging from 10 kW to 40 kW and summarized them in the table here:

How Many Amps Do 10-40 kW Electric Tankless Water Heaters Draw?

In all these calculations, we presume that the heater is running on a 240-volt circuit.

Using this amp draw table, you can accurately estimate how many amps does you tankless hot water heater use. You can then decide about how many amp breakers you’ll need for installation.

If you’re in the market for a tankless water heater, you can check our list of the best tankless units here.