The vast majority of residential electric water heaters — from 30 to 80+ gallons — require a 30-amp double-pole breaker. This is because most standard tank water heaters use either a 4,500W or 5,500W heating element, which draws 18.75–22.9 amps at 240V. With the continuous-load safety factor, a 30A breaker is the correct size.
The tank capacity (gallons) doesn't directly determine breaker size — the heating element wattage does. A compact 30-gallon and a large 80-gallon tank often use identical 4,500W elements, requiring the same 30A breaker.
Water Heater Breaker Size Chart (By Wattage)
| Element Wattage | Amps at 240V | Continuous Load (×1.25) | Required Breaker | Wire Gauge |
|---|---|---|---|---|
| 1,500W | 6.25A | 7.8A | 15A DP | 14 AWG |
| 2,000W | 8.3A | 10.4A | 15A DP | 14 AWG |
| 2,500W | 10.4A | 13.0A | 15A DP | 14 AWG |
| 3,000W | 12.5A | 15.6A | 20A DP | 12 AWG |
| 3,500W | 14.6A | 18.2A | 20A DP | 12 AWG |
| 4,000W | 16.7A | 20.8A | 25A or 30A DP | 10 AWG |
| 4,500W | 18.75A | 23.4A | 30A DP | 10 AWG |
| 5,000W | 20.8A | 26.0A | 30A DP | 10 AWG |
| 5,500W | 22.9A | 28.6A | 30A DP | 10 AWG |
| 6,000W | 25.0A | 31.3A | 40A DP | 8 AWG |
DP = Double-Pole. All electric water heaters operate on 240V, which requires a double-pole breaker connected to both bus bars in your electrical panel. A single-pole breaker only provides 120V and won't work. Double-pole breakers occupy two adjacent slots in your panel.
Water Heater Breaker Size Chart (By Tank Size)
Tank size correlates loosely with element size, but the nameplate wattage is what matters. Here are typical configurations:
| Tank Size (Gallons) | Common Element(s) | Amps | Breaker | Wire | Notes |
|---|---|---|---|---|---|
| 6–20 (point-of-use) | 1,500–2,500W | 6.25–10.4A | 15–20A DP | 14–12 AWG | Under-sink units |
| 20–30 (compact) | 3,000–4,000W | 12.5–16.7A | 20–25A DP | 12–10 AWG | Apartments, small homes |
| 30–40 (standard) | 4,500W | 18.75A | 30A DP | 10 AWG | Most common residential |
| 40–50 (standard) | 4,500W | 18.75A | 30A DP | 10 AWG | Most common residential |
| 50–65 (large) | 4,500–5,500W | 18.75–22.9A | 30A DP | 10 AWG | Larger families |
| 65–80 (extra-large) | 5,500W | 22.9A | 30A DP | 10 AWG | Large families, high demand |
| 80–120 (commercial) | 5,500–6,000W | 22.9–25A | 30–40A DP | 10–8 AWG | Commercial applications |
Why Most Tanks Use 4,500W Elements
Manufacturers standardize on 4,500W because:
- It fits standard wiring: 4,500W ÷ 240V = 18.75A, which stays comfortably under a 30A breaker
- It provides adequate recovery: A 4,500W element heats about 21 gallons per hour — enough for typical household use
- It's energy-efficient enough: Larger elements draw more power without proportionally faster recovery
Larger tanks (65–80 gallons) sometimes use 5,500W elements for faster recovery, but they still fit on a 30A circuit because 22.9A × 1.25 = 28.6A, which rounds up to 30A.
How to Calculate Breaker Size
Step 1: Find the Element Wattage
Check your water heater's data plate (usually on the side of the tank near the access panel). Look for:
- Wattage (W): The total power draw (e.g., 4500W)
- Voltage (V): Should be 240V or 208/240V
- Amps (A): May be listed directly
If only watts and volts are listed: Amps = Watts ÷ Volts
Step 2: Apply the Continuous Load Factor
Water heaters are considered continuous loads because they can run for 3+ hours during heavy hot water use. NEC 422.13 requires:
Required Breaker Ampacity = Actual Amps × 1.25
This 125% factor provides a safety margin for sustained operation.
Step 3: Select the Breaker
Choose the next standard breaker size equal to or greater than the calculated ampacity.
Standard residential double-pole breaker sizes: 15A, 20A, 25A, 30A, 35A, 40A, 45A, 50A, 60A
Example calculation — 4,500W water heater:
- Amps = 4,500W ÷ 240V = 18.75A
- Continuous load = 18.75A × 1.25 = 23.44A
- Next standard breaker = 25A or 30A
- Industry standard = 30A double-pole
Most electricians use 30A rather than 25A because 25A breakers are less common and 30A provides additional margin for voltage fluctuations.
Tankless Water Heater Breaker Requirements
Tankless electric water heaters are completely different from tank units. They require significantly more power and multiple circuits.
| Tankless kW Rating | Total Amps | Number of Breakers | Breaker Size (each) | Total Panel Amps |
|---|---|---|---|---|
| 8 kW | 33A | 1 | 40A DP | 40A |
| 11 kW | 46A | 1 | 60A DP | 60A |
| 13 kW | 54A | 2 | 30A DP | 60A |
| 18 kW | 75A | 2 | 40A DP | 80A |
| 24 kW | 100A | 2 | 50A DP | 100A |
| 27 kW | 113A | 3 | 40A DP | 120A |
| 29 kW | 121A | 3 | 50A DP | 150A |
| 36 kW | 150A | 4 | 40A DP | 160A |
Tankless electric water heaters can overwhelm residential panels. A 27 kW unit requires 120A of breaker capacity — 60% of a 200A panel. Before installing a tankless electric unit, have an electrician verify your panel can handle the additional load. In many cases, a panel upgrade is required.
Heat Pump Water Heater Breaker Size
Heat pump water heaters are the most efficient electric option. They use the same breaker as standard tanks but consume far less energy.
| Type | Wattage (Heat Pump Mode) | Wattage (Backup Mode) | Breaker | Wire |
|---|---|---|---|---|
| Hybrid (normal use) | 500–600W | N/A | 30A DP | 10 AWG |
| Hybrid (backup heating) | 4,500W | 4,500W | 30A DP | 10 AWG |
| Heat pump only | 500–600W | N/A | 30A DP | 10 AWG |
Heat pump water heaters have a backup resistance element (typically 4,500W) that activates during high-demand periods or cold ambient temperatures. The circuit is sized for this worst-case scenario, hence the 30A breaker requirement — same as a standard tank.
The energy savings come from normal operation, where the unit runs almost entirely on the heat pump (500–600W) rather than resistance heating.
Common Breaker Sizing Mistakes
Mistake 1: Using a Single-Pole Breaker
Wrong: Installing a 30A single-pole breaker for a 240V water heater.
Why it fails: Single-pole breakers supply 120V from one bus bar. Water heaters need 240V, which requires connections to both bus bars via a double-pole breaker. A single-pole breaker will either fail to power the heater at all or supply only 120V (1/4 the heating power).
Fix: Always use a double-pole breaker for 240V appliances.
Mistake 2: Undersizing the Breaker
Wrong: Using a 20A breaker for a 4,500W water heater because "it only draws 18.75A."
Why it's a code violation: NEC requires continuous loads (3+ hours) to be limited to 80% of breaker capacity. A 20A breaker allows only 16A continuous — the 18.75A draw exceeds this limit. The breaker may nuisance-trip or overheat.
Fix: Apply the 1.25× factor. 18.75A × 1.25 = 23.4A → use a 30A breaker.
Mistake 3: Oversizing the Breaker (More Dangerous)
Wrong: Using a 40A or 50A breaker on 10 AWG wire "to stop nuisance tripping."
Why it's dangerous: The breaker protects the wire, not the appliance. If you put a 40A breaker on 10 AWG wire (rated 30A), the wire can overheat and start a fire before the breaker trips.
Fix: If breaker trips repeatedly, diagnose the cause — bad element, loose connection, short circuit. Never upsize the breaker without upsizing the wire.
Mistake 4: Not Matching Wire to Breaker
Wrong: Using leftover 12 AWG wire with a 30A breaker.
Why it's a fire hazard: 12 AWG wire is rated for only 20A per NEC 240.4(D). A 30A breaker allows 50% more current than the wire can safely carry. The wire overheats inside the wall before the breaker trips.
Fix: Always match wire to breaker: 30A = 10 AWG, 20A = 12 AWG, 15A = 14 AWG.
Real-World Examples
Example 1: Standard 50-Gallon Tank Replacement
Scenario: Replacing old 50-gallon water heater. Existing circuit: 30A double-pole breaker, 10/2 NM-B wire.
New water heater nameplate: 4,500W, 240V
Calculation: 4,500 ÷ 240 = 18.75A × 1.25 = 23.4A → 30A breaker
Verdict: Existing 30A circuit is correct. No changes needed — just connect the new water heater.
Example 2: Upgrading from 30-Gallon to 65-Gallon
Scenario: Upgrading from compact 30-gallon (3,000W) to large 65-gallon (5,500W). Existing circuit: 20A breaker, 12/2 wire.
New calculation: 5,500 ÷ 240 = 22.9A × 1.25 = 28.6A → 30A breaker
Problem: Existing 12 AWG wire can only support 20A. 30A breaker on 12 AWG = fire hazard.
Solution: Run new 10/2 NM-B cable and install 30A double-pole breaker. Do not reuse the existing wire.
Example 3: Adding Tankless Under-Sink Unit
Scenario: Installing 4 kW point-of-use tankless under kitchen sink for instant hot water.
Calculation: 4,000 ÷ 240 = 16.7A × 1.25 = 20.8A → 25A or 30A breaker
Wire: 10 AWG minimum (30A) or 12 AWG with 20A if the unit draws under 16A (check specs)
Panel impact: One additional double-pole breaker, minimal compared to whole-house tankless.
Example 4: Converting from Gas to Electric
Scenario: Gas water heater failed; homeowner wants to switch to electric 50-gallon tank. No existing 240V circuit to water heater location.
Required new circuit:
- Breaker: 30A double-pole
- Wire: 10/2 NM-B
- Run: 40 feet (basement to water heater location)
- Cost: Materials $60–$100, professional install $250–$500
Panel check: Verify panel has two adjacent open slots for the double-pole breaker.
Key Takeaways
- 30A double-pole breaker is the standard for residential tank water heaters (4,500W–5,500W elements)
- Wire must match breaker: 30A breaker = 10 AWG wire, 20A breaker = 12 AWG wire
- Tank size doesn't determine breaker size — the element wattage does
- Apply the 1.25× continuous load factor: Actual amps × 1.25 = minimum breaker ampacity
- Tankless electric requires multiple breakers — 2–4 circuits drawing 80–160A total
- Heat pump water heaters use standard 30A circuits — same as tanks, but 60–70% less energy
- Never oversize a breaker to stop tripping — diagnose and fix the actual problem
- Always use double-pole breakers for 240V water heaters
Frequently Asked Questions
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