The circuit breaker size depends on your water heater's amperage rating, which you'll find on the nameplate
Most residential electric water heaters need either a 30-amp or 40-amp double-pole circuit breaker. A 30-amp breaker works for heaters rated 4,000 to 5,500 watts; a 40-amp breaker handles 5,500 to 6,500 watts. You must match the breaker to the heater's actual amperage draw, not guess based on tank size. The nameplate on your water heater lists the voltage and wattage — use those numbers to find the correct breaker size.
Oversizing a breaker is dangerous: it won't trip if the wiring overheats, which can cause a fire. Undersizing one means the breaker trips constantly during normal operation. The breaker must also match the wire gauge running to the heater. A 30-amp breaker requires 10-gauge wire; a 40-amp breaker requires 8-gauge wire. If you're replacing a breaker or installing a new heater, have a licensed electrician verify the wire size before you buy the breaker.
Key Takeaways
- Find the wattage and voltage on your water heater's nameplate, then calculate the amperage by dividing watts by volts.
- A 30-amp double-pole breaker fits most 4,000 to 5,500-watt heaters; a 40-amp breaker fits 5,500 to 6,500-watt heaters.
- The wire running to the heater must match the breaker size: 10-gauge for 30-amp, 8-gauge for 40-amp.
- Never install a breaker larger than the heater's rated amperage, as it will not protect against overheating.
How to find your water heater's amperage rating
Look at the metal or plastic nameplate attached to your water heater's side or top. It lists the voltage (usually 240 volts for electric heaters) and the wattage. If the nameplate is missing or illegible, check the installation manual or the manufacturer's website using your model number.
To convert wattage to amperage, divide the wattage by the voltage. For example, a 5,500-watt heater at 240 volts draws 5,500 ÷ 240 = 22.9 amps. Round up to the next standard breaker size, which would be 30 amps. A 6,000-watt heater at 240 volts draws 25 amps, so you'd use a 40-amp breaker. Standard breaker sizes are 15, 20, 30, 40, 50, and 60 amps — you cannot install a 25-amp or 35-amp breaker.
Why wire gauge matters as much as breaker size
The breaker protects the wire, not the appliance. If the wire is too thin for the breaker size, the wire will overheat before the breaker trips. A 30-amp breaker must have 10-gauge copper wire (or 8-gauge aluminum, though copper is standard). A 40-amp breaker requires 8-gauge copper wire. A 50-amp breaker requires 6-gauge copper wire.
If you're replacing an old breaker and the existing wire is undersized, you have two choices: replace the wire with the correct gauge, or install a smaller breaker that matches the existing wire. Replacing the wire is more expensive but safer and more reliable. Never install a larger breaker to fit existing undersized wire — that defeats the breaker's purpose.
Double-pole breakers are required for 240-volt heaters
All residential electric water heaters run on 240 volts, which requires a double-pole breaker. A double-pole breaker has two switches that trip together and controls two hot wires. It looks wider than a single-pole breaker and takes up two spaces in your breaker panel.
Do not use a single-pole breaker for a water heater, even if the amperage seems to match. A single-pole breaker controls only one hot wire and is designed for 120-volt circuits like outlets and lights. Using one on a 240-volt heater will not protect the circuit properly and creates a fire hazard.
Common breaker sizes and the heaters they fit
| Breaker Size | Wire Gauge (Copper) | Heater Wattage Range | Typical Amperage Draw |
|---|---|---|---|
| 30 amps | 10 gauge | 4,000–5,500 watts | 17–23 amps |
| 40 amps | 8 gauge | 5,500–6,500 watts | 23–27 amps |
| 50 amps | 6 gauge | 9,600–12,000 watts | 40–50 amps |
Most homes have 30-amp or 40-amp breakers for their water heaters. Larger heaters (9,600 watts or more) or homes with multiple heaters may need 50-amp or 60-amp breakers. Tankless electric water heaters often draw 40 to 50 amps because they heat water on demand with high power.
The table above shows the most common combinations, but your specific heater may differ. Always check the nameplate first, then cross-reference with the breaker and wire requirements. If you find a mismatch between what the nameplate says and what's currently installed, that's a sign to call an electrician before using the heater.
What to do if you're unsure about your setup
If the nameplate is missing, the wiring looks old or damaged, or you're not confident in your math, contact a licensed electrician. They can inspect the heater, measure the wire gauge, and tell you the correct breaker size. This costs less than replacing a water heater after an electrical fire.
If you're installing a new water heater, the manufacturer's installation guide will specify the required breaker size and wire gauge. Follow those specifications exactly. If the guide calls for a 40-amp breaker and 8-gauge wire, do not substitute a 30-amp breaker or 10-gauge wire to save money — the heater may not work properly, or the circuit may overheat.
Frequently Asked Questions
Can I use a 50-amp breaker on a 5,500-watt water heater?
No. A 50-amp breaker is too large and will not trip if the heater or wiring overheats. The breaker must match the heater's amperage rating. A 5,500-watt heater at 240 volts draws about 23 amps and needs a 30-amp breaker.
What if my water heater draws 24 amps — do I use a 20-amp or 30-amp breaker?
Use a 30-amp breaker. Always round up to the next standard breaker size. A 20-amp breaker would trip constantly during normal operation. The 30-amp breaker is the next size up and will handle 24 amps safely.
Can I replace a 30-amp breaker with a 40-amp breaker to stop it from tripping?
Only if your water heater actually draws more than 30 amps and the wire is 8-gauge or larger. If the breaker is tripping because the heater draws 22 amps, upgrading to 40 amps will not solve the problem — the issue is likely a loose connection or a failing heater element. Have an electrician diagnose the cause before changing the breaker.
Do I need a new breaker if I'm replacing my water heater with the same model?
Not necessarily. If the new heater has the same wattage and voltage as the old one, the existing breaker and wire will work. Check the nameplate on the new heater to confirm it matches the old one. If the new heater is a different wattage, you may need a different breaker size.
What's the difference between a 30-amp breaker for a water heater and a 30-amp breaker for a dryer?
Both are 30-amp double-pole breakers and look identical, but they protect different circuits. The breaker itself is the same; what matters is the wire gauge and the appliance's amperage rating. Always match the breaker to the specific appliance's requirements, not to another appliance's breaker.