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:
- total power or wattage. Electric tankless water heaters can have a power input of 10,000W (10 kW) to 40,000W (40 kW).
- 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.
Tankless Heater Size (in KW) | Electric current (in amps) |
10 kW | 42 amperes |
11 kW | 46 amps |
12 kW | 50 amps |
13 kW | 54 amps |
14 kW | 58 amps |
15 kW | 63 amperes |
16 kW | 67 amperes |
17 kW | 71 amperes |
18 kW | 75 amps |
19 kW | 79 amperes |
20 kW | 83 amperes |
21 kW | 88 amps |
22 kW | 92 amperes |
23 kW | 96 amperes |
24 kW | 100 amperes |
25 kW | 104 amps |
26 kW | 108 amperes |
27 kW | 113 amperes |
28 kW | 117 amperes |
29 kW | 121 amperes |
30 kW | 125 amps |
31 kW | 129 amperes |
32 kW | 133 amperes |
33 kW | 138 amps |
34 kW | 142 amperes |
35 kW | 146 amperes |
36 kW | 150 amps |
37 kW | 154 amperes |
38 kW | 158 amperes |
39 kW | 163 amperes |
40 kW | 167 amperes |
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.
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