You're installing or replacing an electric water heater and need to know what size wire and breaker it takes. Get it right and it's a straightforward job; get the wire undersized and it's a fire risk, so this is worth confirming against the code, not guessing.
This guide gives the wire and breaker sizes for tank, tankless and heat-pump water heaters, the NEC math behind them, and the details that trip people up (like why a tank with two heating elements still only needs a 30-amp circuit). The wire sizes follow the National Electrical Code. A new or replaced water-heater circuit usually requires a permit and inspection, and the work is safety-critical, so if you're not confident, have a licensed electrician do or verify it.
Most standard electric tank water heaters (3,500 to 5,500 watts) use 10 AWG copper wire on a 30-amp double-pole breaker, on a dedicated 240-volt circuit. That combination covers the large majority of residential tanks. Tankless electric units draw far more power and need much larger wiring (often 6 AWG or multiple circuits), and heat-pump water heaters use the same 10 AWG / 30-amp setup as standard tanks.
Quick reference: wire size by water heater type
Standard electric tank heaters
| Wattage (at 240V) | Amp draw | Wire | Breaker |
|---|---|---|---|
| 3,000–3,500W | ~12.5–14.6A | 12 AWG | 20A double-pole |
| 4,000–5,500W | ~16.7–22.9A | 10 AWG | 30A double-pole |
The vast majority of residential tanks use a 4,500W element and land on 10 AWG / 30A. Use 10/2 NM-B cable (two conductors plus ground); a water heater doesn't need a neutral, so 10/3 is only for units that specifically call for one.
Electric tankless heaters (much higher demand)
Tankless electric units heat water instantly, which takes a lot of power, so they need substantially heavier wiring, often more than one circuit:
| Size | Approx. amp draw (240V) | Typical wiring |
|---|---|---|
| 8–11 kW | ~33–46A | 6 AWG, single 50–60A circuit |
| 13–18 kW | ~54–75A | Two circuits (commonly 8 AWG / 40A each) |
| 24–36 kW | ~100–150A | Three to four circuits, or heavier feeders |
Because tankless requirements vary so much by model and can approach or exceed a typical panel's capacity, always size to the specific unit's nameplate and confirm your panel can handle it. Whole-home electric tankless often requires an electrical service evaluation, this is a common case where a panel upgrade is needed.
Heat-pump (hybrid) water heaters
| Mode | Amp draw | Wire | Breaker |
|---|---|---|---|
| Hybrid (heat pump + backup element) | ~2–19A | 10 AWG | 30A double-pole |
Heat-pump water heaters use the same 10 AWG / 30A circuit as a standard tank (the backup resistance element is the same as a tank's), while using far less energy in normal operation.
The NEC math behind the standard
The 10 AWG / 30A standard for tank heaters comes from a straightforward code calculation. A water heater is treated as a continuous load under the NEC, which means the circuit is sized to 125% of the steady draw:
For a 4,500W element at 240V:
- Amp draw = 4,500 ÷ 240 = 18.75A
- Continuous-load requirement = 18.75 × 1.25 = 23.4A
- Next standard breaker up = 30A
- Wire for a 30A circuit = 10 AWG
For a 5,500W element at 240V:
- Amp draw = 5,500 ÷ 240 = 22.9A
- Continuous-load requirement = 22.9 × 1.25 = 28.6A
- Breaker = 30A (the NEC specifically permits a 30A breaker for water heaters rated up to 5,500W)
- Wire = 10 AWG
So both common element sizes land on the same 10 AWG / 30A circuit, which is why it's the near-universal residential standard.
Why two elements still only need a 30-amp circuit
Most tank water heaters have two heating elements, upper and lower, which surprises people into thinking they need to size for both at once. They don't. A thermostat energizes only one element at a time, never both together, so the circuit is sized for a single element's draw (4,500W), not the combined 9,000W.
The one exception: some commercial or high-recovery units are designed for simultaneous operation of both elements. Those genuinely do need a larger circuit (typically 6 AWG on a 50A breaker, or two separate circuits). This is uncommon in homes, always check the nameplate to see whether your unit is simultaneous or (far more likely) non-simultaneous.
The rules that keep it safe
A few code points that matter for any water-heater circuit:
- Dedicated circuit. A water heater must be on its own circuit powering nothing else. Sharing it violates code and risks overloading.
- Match wire to breaker. A 30A breaker requires 10 AWG; never put a smaller wire on a larger breaker. This is the pairing that prevents overheating.
- 240V uses a double-pole breaker (it connects to both hot legs). Single-pole breakers are only for 120V point-of-use units.
- Confirm the nameplate. Size from the unit's actual rated wattage, not an assumption or the old unit's wiring. And a metal plumbing system may require a bonding jumper per local code.
- Permit and inspection. Most jurisdictions require a permit for a water-heater circuit, and the inspection is there precisely because a wiring error on this kind of load is a fire risk.
If any of this is outside your comfort zone, this is a job for a licensed electrician, the cost of doing it right is small next to the risk of an undersized or improperly connected circuit.
Energy and incentives (2026)
Heat-pump water heaters are the efficiency standout, using the same wiring as a standard tank but far less energy in normal operation (they move heat rather than generating it with resistance elements). On incentives, the rules changed recently: the federal Section 25C tax credit (which had covered up to $2,000 for qualifying ENERGY STAR heat-pump water heaters) expired for installs placed in service after December 31, 2025 under the OBBBA. For 2026, the active pathways are:
- IRA HEAR (income-qualified, up to $1,750 for a heat-pump water heater)
- IRA HOMES (performance-based)
- State and utility rebates
Check the DSIRE database for what your area currently offers.
Frequently asked questions
What size wire does a water heater need? Most residential electric tank water heaters (4,500 to 5,500W) need 10 AWG copper wire on a 30-amp double-pole breaker, using 10/2 cable on a dedicated 240V circuit. Smaller units (3,000 to 3,500W) can use 12 AWG on a 20A breaker. Always confirm against your unit's nameplate.
What size breaker for a 4,500-watt water heater? A 30-amp double-pole breaker. The 4,500W element draws 18.75A, and the NEC's 125% continuous-load rule brings that to 23.4A, which rounds up to a 30A breaker on 10 AWG wire.
Do tankless water heaters need special wiring? Yes, much heavier. Electric tankless units draw far more power than tank heaters (often 40 to 150 amps) and frequently need multiple circuits and heavier wire (6 AWG or larger), and sometimes an electrical panel upgrade. Size strictly to the unit's nameplate and have an electrician confirm your panel can support it.
Can I use 10/3 wire instead of 10/2 for a water heater? You can, but you usually don't need to. A standard water heater doesn't use a neutral, so 10/2 (two hots plus ground) is correct. Use 10/3 only if your specific unit requires a neutral for a digital control or timer, which is uncommon, check the wiring diagram.
Do I need a permit to install a water heater circuit? In most jurisdictions, yes. A new or replaced water-heater circuit typically requires a permit and inspection, and because a wiring error on this load is a fire risk, the inspection is a genuine safety check. If you're not confident with the electrical work, have a licensed electrician handle it.
About these figures
The wire and breaker sizes, and the sizing method (a water heater is a continuous load, so the circuit is sized to 125% of the steady draw per NEC 210.19, and a 30-amp breaker is permitted for water heaters rated up to 5,500W per NEC 422.11(E)(3)), follow the National Electrical Code (NEC / NFPA 70). Because conductor sizing depends on the specific unit, the wire type, and installation conditions, the sizes here are standard references, confirm against your water heater's nameplate and your local code, and have the work done or verified by a licensed electrician.
The tax-credit and rebate information reflects current federal rules: the IRS Section 25C credit (expired for installs placed in service after December 31, 2025 under the OBBBA) and the active IRA HEAR and HOMES rebate programs, with state and utility incentives tracked in the DSIRE database. NFPA 70 is the authoritative U.S. electrical standard, adopted (sometimes with amendments) by your local jurisdiction.
Sources & References
Related Articles
3-Phase Power Calculator: kW to Amps, Amps to kW (2026)
calculator • 5 min read
Electrical Panel Upgrade Cost: 100 to 200 Amp (2026 Guide)
cost-guide • 8 min read
How Many Amps Does a House Use? (Service Size and Load, 2026)
explainer • 7 min read
Wire Size for 220V/240V Circuits (30, 40 & 50 Amp): NEC Reference & the 4 Factors That Change It
guide • 9 min read