A standard electric tank water heater draws 18.75 amps at 240 volts (for a 4,500W element) or 22.9 amps (for a 5,500W element). Tankless electric water heaters are power-hungry — drawing 33 to 150 amps depending on size. Heat pump water heaters draw only 2–3 amps during normal operation, making them the most efficient option.
Understanding your water heater's amp draw is essential for proper circuit sizing. An undersized circuit means nuisance breaker trips; an oversized breaker on undersized wire is a fire hazard.
Water Heater Amp Draw Quick Reference
| Water Heater Type | Typical Amps | Circuit Required | Wire Gauge |
|---|---|---|---|
| Tank (4,500W) | 18.75A | 30A / 240V | 10 AWG |
| Tank (5,500W) | 22.9A | 30A / 240V | 10 AWG |
| Tankless (18kW) | 75A total | 2 × 40A / 240V | 8 AWG each |
| Tankless (27kW) | 113A total | 3 × 40A / 240V | 8 AWG each |
| Heat pump (normal mode) | 2–3A | 30A / 240V | 10 AWG |
| Heat pump (backup mode) | 18.75A | 30A / 240V | 10 AWG |
Tank Water Heater Amp Draw Chart
| Element Wattage | Voltage | Amps | Continuous Load (×1.25) | Breaker |
|---|---|---|---|---|
| 1,500W | 240V | 6.25A | 7.8A | 15A DP |
| 2,500W | 240V | 10.4A | 13.0A | 15A DP |
| 3,000W | 240V | 12.5A | 15.6A | 20A DP |
| 4,000W | 240V | 16.7A | 20.8A | 25A DP |
| 4,500W | 240V | 18.75A | 23.4A | 30A DP |
| 5,500W | 240V | 22.9A | 28.6A | 30A DP |
| 6,000W | 240V | 25.0A | 31.3A | 40A DP |
The 4,500W / 18.75A configuration covers 80–90% of residential water heaters. This applies to tanks from 30 to 80 gallons. If you don't know your specific wattage, 18.75A is a reliable estimate — but always verify from the data plate on your unit.
Tankless Electric Water Heater Amps
Tankless units heat water instantly on demand, requiring massive power draws.
| Model kW | Total Amps | Circuits Needed | Amps per Circuit | Panel Load |
|---|---|---|---|---|
| 8 kW | 33A | 1 | 33A | 40A |
| 11 kW | 46A | 1 | 46A | 60A |
| 13 kW | 54A | 2 | 27A | 60A |
| 18 kW | 75A | 2 | 37.5A | 80A |
| 24 kW | 100A | 2 | 50A | 100A |
| 27 kW | 113A | 3 | 37.7A | 120A |
| 36 kW | 150A | 4 | 37.5A | 160A |
Tankless electric water heaters can overwhelm residential panels. A 27kW unit requires 113 amps — over half of a 200A panel. Many homes need a panel upgrade before installing tankless electric. Consider a heat pump water heater instead — same 30A circuit, far lower actual draw.
Heat Pump Water Heater Amps
Heat pump water heaters use refrigeration technology to extract heat from surrounding air, dramatically reducing energy consumption.
| Operating Mode | Wattage | Amps at 240V | When Used |
|---|---|---|---|
| Heat Pump Only | 500–600W | 2.1–2.5A | Normal operation, ambient >45°F |
| Hybrid | 500–4,500W | 2.1–18.75A | Auto-selects based on demand |
| Electric Only | 4,500W | 18.75A | High demand or cold ambient |
| High Demand | 4,500W | 18.75A | Rapid recovery needed |
The key insight: Heat pump water heaters are wired identically to standard tanks (30A circuit, 10 AWG wire) but draw only 2–3 amps during typical operation. The circuit is sized for the backup resistance element, which rarely activates.
How to Calculate Your Water Heater's Amps
Formula: Amps = Watts ÷ Volts
Example: 4,500W water heater at 240V 4,500 ÷ 240 = 18.75 amps
Finding the Wattage
Look for the data plate on your water heater (usually near the upper thermostat access panel). It lists:
- Watts (W): Element wattage
- Volts (V): Operating voltage (240V)
- Amps (A): Sometimes listed directly
Note: If you see "4500/4500W" (dual elements), only one operates at a time. Size your circuit for single-element draw (4,500W), not combined.
Amp Draw vs. Operating Cost
| Water Heater Type | Monthly kWh | Monthly Cost ($0.166/kWh) | Annual Cost |
|---|---|---|---|
| Standard tank (4,500W) | 400–500 | $66–$83 | $797–$996 |
| High-efficiency tank | 350–420 | $58–$70 | $697–$837 |
| Heat pump (hybrid) | 130–180 | $22–$30 | $259–$359 |
| Tankless (18kW, moderate use) | 280–400 | $46–$66 | $558–$797 |
Cost comparison for a family of 4:
- Standard tank: $70/month ($840/year)
- Heat pump water heater: $26/month ($312/year)
- Annual savings: $528
The heat pump pays for itself in 3–4 years through energy savings alone — faster with the $2,000 federal tax credit available through 2032.
Dual Elements: A Common Confusion
Most residential water heaters have two heating elements (upper and lower), but they never run simultaneously. Here's how the sequencing works:
- Cold water enters the tank
- Upper element heats first (hot water rises to top for immediate use)
- Upper thermostat satisfies, transfers power to lower element
- Lower element heats the rest of the tank
- Cycle repeats as hot water is used
Circuit sizing: Based on one element (4,500W = 18.75A), not both combined.
Real-World Examples
Example 1: Verifying Circuit for Replacement
Scenario: Replacing a 50-gallon water heater. Existing circuit: 30A breaker, 10/2 NM-B.
New water heater specs: 4,500W, 240V
Calculation:
- Amps = 4,500 ÷ 240 = 18.75A
- With 1.25× factor: 18.75 × 1.25 = 23.4A
- Required breaker: 25A or 30A ✓
Verdict: Existing 30A circuit is correct. Compatible without changes.
Example 2: Tankless vs. Heat Pump Decision
Scenario: Family wants to upgrade from standard tank. Current panel: 200A with 40A spare capacity.
Option A: Tankless 27kW
- Requires 113A (3 × 40A circuits)
- Exceeds 40A spare capacity
- Would need panel upgrade ($1,500–$4,000)
Option B: Heat Pump
- Requires 30A (one circuit)
- Draws only 2–3A normally
- Fits existing panel easily
Best choice: Heat pump — lower installation cost, lower operating cost, no panel upgrade.
Example 3: Converting Gas to Electric
Scenario: Gas water heater failed; homeowner switching to electric 50-gallon tank.
New circuit needed:
- Breaker: 30A double-pole
- Wire: 10/2 NM-B
- Run: 35 feet from panel
- Panel spaces: 2 (for double-pole breaker)
Cost: $250–$500 professional installation (plus water heater)
Key Takeaways
- Standard tank water heater: 18.75 amps (4,500W at 240V) — the most common configuration
- Tankless electric: 33–150 amps — often requires panel upgrades
- Heat pump: 2–3 amps normal operation — most efficient option, same 30A circuit
- Formula: Amps = Watts ÷ Volts — verify from nameplate
- Dual elements don't run simultaneously — circuit sized for single-element draw
- 30A breaker + 10 AWG wire covers 90%+ of residential tank water heaters
- Heat pumps save $400–$600/year vs. standard tanks with identical wiring requirements