What Size Circuit Breaker Does a Water Heater Need?
Electric water heater circuit sizing depends on whether you have a tank or tankless unit — they have very different electrical requirements. Get this wrong and your breaker either trips constantly or your wiring runs undersized for the load.
Tank electric water heater circuit breaker size
Standard residential tank water heater (30–80 gallon): 30A double-pole circuit breaker, 240V dedicated circuit, 10 AWG wire
Most residential electric tank water heaters draw 3,500–4,500 watts at 240V. At 4,500W divided by 240V, that's 18.75A — well within a 30A circuit. The 30A circuit also provides 25% headroom per the 80% rule (maximum
24A continuous on a 30A breaker). This is why 30A is universal for tank water heaters.
Verify on your unit: The nameplate on the side of the water heater lists the wattage and voltage. If yours is rated above 5,500 watts, it may require a 40A circuit — check the installation manual.
Browse replacement circuit breakers (/collections/2-pole) — we stock direct-fit replacements for all major panel brands.
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Tankless electric water heater circuit breaker size
Tankless water heaters are a completely different story. Because they heat water instantly on demand (rather than maintaining a stored tank), they draw enormous current in short bursts.
Typical tankless requirements:
- Whole-house electric tankless: 2–3 separate 40A–60A double-pole circuits, often totaling 150A or more
- Point-of-use tankless (single sink): 1 circuit at 20A–30A
A typical whole-house tankless installation requires a panel with 200A service and may require a panel upgrade if your current service is only 100A. This is not a plug-in appliance — it's a major electrical
installation. Always check the manufacturer's installation guide before purchasing.
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Gas water heater circuit breaker size
Gas water heaters use gas for heat. Electricity only powers:
- The electronic igniter
- The control board
- The display/thermostat
This requires only a standard 20A single-pole (120V) outlet circuit — the same as any general-purpose outlet. Most gas water heaters plug into a standard 3-prong outlet. No dedicated circuit is required by code, though
some installers recommend one.
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How to read your water heater nameplate
Every electric water heater has a nameplate label on the side of the unit (often near the top or bottom panel). Look for:
- Voltage: Should say 240V or 208–240V
- Wattage: Typically 3,500W–5,500W for residential tank units
- Max amperage or breaker size: Some labels specify this directly
To calculate the correct breaker size from wattage: divide watts by 240 to get amps, then divide by 0.8 (the 80% rule) to get the minimum breaker rating. A 4,500W element: 4,500 ÷ 240 = 18.75A ÷ 0.8 = 23.4A → round up
to the next standard size = 30A.
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When the water heater circuit breaker needs replacing
If your water heater breaker trips frequently or won't stay reset, the most common causes are:
1. A worn-out breaker — After 20+ years, breakers drift out of calibration and trip prematurely. Replace with an identical 30A double-pole unit.
2. A failing heating element — A shorted heating element draws excess current, tripping the breaker. If a new breaker trips immediately, the element is likely the cause.
3. Loose wiring connections — Check terminal screws at the breaker and at the water heater junction box. Loose connections cause resistance, heat, and intermittent tripping.
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FAQ
Can I use a 40A breaker for a water heater on 10 AWG wire?
No. A 40A breaker requires 8 AWG wire. Putting a 40A breaker on 10 AWG wiring means the wire can overheat before the breaker trips. If you need to upsize to 40A for a higher-wattage unit, the wire must be upgraded to 8
AWG at the same time.
Does a water heater need a GFCI breaker?
Under the 2023 NEC, electric water heaters in certain locations may require GFCI protection. Check your local code. In most residential applications with a typical tank water heater in a utility room, a standard 30A
double-pole breaker without GFCI is still acceptable.
My water heater breaker trips every few days — what's wrong?
The most common causes are a failing heating element (causes current spikes), a worn breaker, or loose connections at the terminal. Start by turning off the breaker, checking that all wire connections are tight, and
resetting. If it trips again within a day or two, the heating element or breaker needs replacement. See our guide on why circuit breakers keep tripping (/blogs/news/circuit-breaker-keeps-tripping) for a full
diagnostic.
What size breaker does a hybrid heat pump water heater need?
photo of "Siemens, QOB360, 60A, Circuit Breaker"
Most hybrid heat pump water heaters (like Rheem ProTerra or A.O. Smith Voltex) require a 30A double-pole circuit — same as a standard electric tank. Confirm on the unit's nameplate. The heat pump mode draws far less
current than the resistance backup element, so 30A handles both modes.