Electric tankless heaters rely only on electricity to warm up the water in their tanks.

As is common knowledge, heating water is a relatively labor-intensive process.

Because of this, electric tankless water heaters need for a substantial amount of amps, which stands for amperes.

How many amps are needed to power a tankless water heater?

The amount of current that tankless heaters require may range anywhere from 42 to 167 amps.

Because of these two crucial parameters, we are able to compute the precise number of amps that are required by a tankless water heater:

  1. Total power, often known as watts. Electric tankless water heaters have a power intake that ranges anywhere from 10,000 watts to 40,000 watts (40 kW).
  2. Voltage. Every electric tankless water heater runs on a 240-volt circuit so that the current draw may be kept to a minimum.

Using the equation for electric power, which is P = IV, we are able to compute the by expressing the I, also known as the electric current, as follows:

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

Example: Consider the following scenario: we have a tankless water heater with 240 volts and 30 kW of power.

How many amps does a tankless water heater with 30 kW need to operate? The following is an example of how we apply the electrical power equation:

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

This kind of heater uses 125 amps of electricity (you need several 20-amp or 30-amp breakers for installation).

The results of our calculations for the amp draws of tankless water heaters with capacities ranging from 10 kW to 40 kW are presented in the table below:

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

For the sake of all of these calculations, we will assume that the heater is connected to a circuit that operates at 240 volts.

Tankless Heater Size (in kW)Electrical Current (in Amps)
10 kW42 amps
11 kW46 amps
12 kW50 amps
13 kW54 amps
14 kW58 amps
15 kW63 amps
16 kW67 amps
17 kW71 amps
18 kW75 amps
19 kW79 amps
20 kW83 amps
21 kW88 amps
22 kW92 amps
23 kW96 amps
24 kW100 amps
25 kW104 amps
26 kW108 amps
27 kW113 amps
28 kW117 amps
29 kW121 amps
30 kW125 amps
31 kW129 amps
32 kW133 amps
33 kW138 amps
34 kW142 amps
35 kW146 amps
36 kW150 amps
37 kW154 amps
38 kW158 amps
39 kW163 amps
40 kW167 amps

With the help of this amp draw chart, you will be able to make an exact estimation of the number of amps that your tankless hot water heater uses.

After that, you will be able to make a decision on the quantity of amp breakers that will be required for the installation.

You may see our ranked list of the top tankless units here if you are interested in purchasing a tankless water heater in the near future.

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Written by Bob Matsuoka
Bob Matsuoka is a blogger and founder of RVing Beginner blog. He has been blogging for over five years, writing about his own family’s RV adventures, tips for people who are interested in buying an RV or taking their family on an adventure by RV.