What Size Breaker for a Water Heater?
- Appliance
- Water Heater
- Scope
- nameplate
- Deciding input
- Nameplate current
- Next
- Compatibility calculator
What Decides the Breaker
Fixed electric water heaters are commonly continuous loads; use the nameplate.
| Input | Sizing basis | Breaker direction | Status |
|---|---|---|---|
| 18.8 A example load | 23.5 A continuous-load sizing | 25 A starting point | Run conductor check |
What Actually Decides the BreakerFor a fixed electric water heater that operates as a continuous load, size the branch circuit to at least 125 percent of the nameplate current, then pick a standard breaker and a conductor that can carry that design current. The nameplate watts divided by volts is only the start.
The 4500 W Heater on a 30 A Myth
The job-site situation behind this search.
A 4500 W, 240 V water heater draws about 18.8 A. People multiply that by nothing, see that 20 A or 30 A looks big enough, and miss the continuous-load sizing step that pushes the circuit to 30 A minimum and often to a conductor check that surprises them on aluminum or long basement runs.
Tankless electric units are a different animal — much higher demand, often multiple circuits — and should not reuse a tank-style answer.
Worked Starting Point
A concrete path for this appliance — not a shared checklist.
Worked Starting Point: 4500 W Storage Heater
Fixed storage electric water heater, 4500 W at 240 V, treated as continuous, copper conductors, 75 C terminations.
- Nameplate current = 4500 W / 240 V = 18.75 A.
- Continuous-load design current = 18.75 A × 1.25 = 23.4 A.
- Next standard breaker at or above 23.4 A is 25 A where used, or more commonly 30 A in residential panels stocked with standard sizes.
- Verify the conductor usable ampacity covers the design current and the chosen breaker under the compatibility rules.
Starting point: about 23.4 A of continuous sizing → commonly a 30 A breaker with a conductor that passes the compatibility check for that rating.
Field Checks for This Appliance
Checks that matter specifically here — not the generic breaker list.
Confirm continuous-load treatment
Storage electric water heaters commonly run long enough to be treated as continuous. Apply the 125 percent sizing step before picking the breaker.
Use nameplate watts and volts
Convert nameplate watts at the stated voltage to amperes. Do not size from a marketing recovery-rate number.
Watch element replacements
Swapping a 3500 W element for 4500 W can invalidate the existing breaker and conductor without anyone changing the panel schedule.
Separate tankless designs
Whole-house tankless electric heaters often need multiple large breakers. This page's single-circuit example does not cover them.