How Many Amps Does a Tankless Electric Water Heater Use?
Tankless Electric Water Heater draws about 75 amps at 240 volts (18,000 watts running). Tankless Electric Water Heater runs on its own dedicated 240 V circuit — plan on two or three 40 A double-pole circuits (8 AWG copper each), per the manufacturer.
Amps = watts ÷ volts. Enter the wattage from your appliance's nameplate or label for an exact figure.
Current draw — a tankless electric water heater
75 A
- At 240 V
- 18,000 W
This appliance's circuit is sized from its nameplate per the NEC, not from wattage — see the circuit guidance below.
Tankless Electric Water Heater amperage at 120 V and 240 V
Same 18,000 W load — the current halves when the voltage doubles. Tankless Electric Water Heater is typically a 240 V appliance in US homes.
| Draw | Watts | Amps at 120 V | Amps at 240 V |
|---|---|---|---|
| Running | 18,000 W | 150 A | 75 A |
Breaker and circuit for a tankless electric water heater
Tankless Electric Water Heater runs on its own dedicated 240 V circuit — plan on two or three 40 A double-pole circuits (8 AWG copper each), per the manufacturer. Large tankless heaters are continuous loads split across multiple circuits — 18 kW needs roughly 94 A of 240 V capacity at 125%, never a single branch circuit.
Guidance only — actual circuit sizing depends on your unit's nameplate, wire run length, and local code. Confirm with a licensed electrician. See the wire & breaker size chart for the full NEC ampacity table.
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