How many amps does a tankless water heater use? (42-167 amps)

Electric tankless heaters use electricity exclusively to heat water. As we know, heating water is a very demanding job. Therefore electric tankless water heaters require a strong electric current; In other words. How many amps do amps tankless water heaters use?

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

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

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

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

I (amps) =p (Watt) / v (volt)

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 electric power equation like this:

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

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

We have calculated amp draw for tankless water heaters 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 of these calculations, we assume that the heater is operating on a 240-volt circuit.

Using this amp draw table, you can accurately estimate how many amps you use a tankless hot water heater. You can then decide how many amp breakers you will need for the installation.

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