# 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 = IÃ—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.

 Tankless Heater Size (in kW) Electrical Current (in Amps) 10 kW 42 amps 11 kW 46 amps 12 kW 50 amps 13 kW 54 amps 14 kW 58 amps 15 kW 63 amps 16 kW 67 amps 17 kW 71 amps 18 kW 75 amps 19 kW 79 amps 20 kW 83 amps 21 kW 88 amps 22 kW 92 amps 23 kW 96 amps 24 kW 100 amps 25 kW 104 amps 26 kW 108 amps 27 kW 113 amps 28 kW 117 amps 29 kW 121 amps 30 kW 125 amps 31 kW 129 amps 32 kW 133 amps 33 kW 138 amps 34 kW 142 amps 35 kW 146 amps 36 kW 150 amps 37 kW 154 amps 38 kW 158 amps 39 kW 163 amps 40 kW 167 amps

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.