Shopping for a tankless water heater—or troubleshooting an install? One of the most important details to get right is the amp draw. Electric tankless water heaters can be surprisingly demanding on your home’s electrical system, and gas units require their own dedicated circuits too. This guide breaks down the typical amperage requirements by size, brand, and application, so you can choose the right heater, plan your electrical panel, and avoid costly mistakes.
Quick Answer: Typical Amp Draw for Tankless Water Heaters
- Electric Tankless Water Heaters: Most whole-house models use 60–150 amps at 240V, requiring multiple 40–60 amp double-pole breakers and heavy-gauge wiring. Point-of-use units use 15–40 amps.
- Gas (Natural Gas/Propane) Tankless Heaters: Usually draw 2–5 amps at 120V, just enough for controls, igniter, and fans. They do NOT heat water electrically.
- Always check your model’s manual or specs before buying or wiring!
Why Amp Draw Matters for Tankless Water Heaters
- Panel Capacity: Your electrical panel must have enough capacity for the heater’s load, plus everything else in your home.
- Breaker & Wire Size: Using undersized breakers or wires is a major fire hazard and can void your warranty.
- Multiple Breakers Needed: Most large electric tankless units require two or three dedicated circuits, each with its own breaker and wiring.
- Permits & Code: Local code and inspectors will check for proper sizing before you can pass inspection.
Real Examples: Amp Draw by Tankless Water Heater Model
| Model | Power | Voltage | Amps | Breakers Needed | Best For | Price Link |
|---|---|---|---|---|---|---|
| Stiebel Eltron Tempra 24 Plus | 24 kW | 240V | 100A | 2 x 50A | Whole house | View |
| EcoSmart ECO 27 | 27 kW | 240V | 112.5A | 3 x 40A | Whole house | View |
| Rheem RTEX-24 | 24 kW | 240V | 100A | 2 x 50A | Whole house | View |
| EcoSmart ECO 11 | 13 kW | 240V | 54A | 1 x 60A | Single bath/sink | View |
| Stiebel Eltron DHC 6-2 | 5.7 kW | 240V | 24A | 1 x 30A | Point-of-use | View |
| Rinnai V65iN (Gas) | N/A | 120V | 2A | 1 x 15A | Whole house | View |
How to Calculate Amps for Electric Tankless Water Heaters
- Formula: Amps = Watts ÷ Volts
- Example: A 24,000-watt (24 kW) heater at 240V draws 100 amps (24,000 ÷ 240 = 100).
- For three-phase power, or lower voltage (110V/120V units), always check the manual—amp draw changes by voltage.
Buyer’s Guide: Choosing the Right Tankless Water Heater for Your Panel
- Check Electrical Panel Capacity: Add up the amp draw for all circuits in use. Most homes with 200-amp service can run one large tankless unit—but check with an electrician before buying.
- Dedicated Circuits Only: Never share circuits between water heaters and other appliances.
- Breaker Size: Follow the manufacturer’s spec. 40–60A double-pole breakers are typical for each circuit.
- Wire Gauge: Use the correct wire size for the amp load—#6 or #8 AWG for most big units.
- Professional Installation: Large tankless heaters should always be installed by a licensed electrician to ensure safety and code compliance.
- Gas Model Requirements: Only need a standard 120V outlet for controls, so almost any home can handle a gas unit’s electrical load.
Top Product Picks: Tankless Water Heaters by Amp Draw
Stiebel Eltron Tempra 24 Plus
- 100A total (2 x 50A), 24 kW at 240V
- Whole-house performance for 2–3 bathrooms
- Digital controls, quiet, and efficient
Final Verdict: The go-to choice for modern homes with enough electrical capacity.
See it on Amazon
EcoSmart ECO 27
- 112.5A (3 x 40A), 27 kW at 240V
- Handles 2–4 bathrooms in warmer climates
- Lifetime warranty (residential)
Final Verdict: Best value for large families who need serious hot water power.
Check price on Amazon
EcoSmart ECO 11
- 54A (1 x 60A), 13 kW at 240V
- Great for a single bathroom, RV, or cabin
- Compact, reliable, and easy to install
Final Verdict: Best for point-of-use or small homes with limited electrical supply.
See details on Amazon
Rinnai V65iN (Gas)
- 2A at 120V (standard outlet)
- Powerful hot water output for most homes
- Requires only minimal electricity for ignition and controls
Final Verdict: Best for homes with limited electrical panel space—no heavy wiring needed.
See details on Amazon
FAQ: Tankless Water Heater Amps & Electrical Requirements
- Can I run a tankless water heater on a 100-amp panel?
Not for large electric models. Most require at least 150–200 amp service. Small point-of-use units may work, but always consult an electrician. - Why do electric tankless heaters use so many amps?
They must instantly heat water on demand—requiring massive power compared to tank models, which heat water slowly over time. - What about gas tankless heaters—do they use much electricity?
No. Gas models use only 2–5 amps at 120V for their controls, not for heating water. - Can I install a tankless heater myself?
Small electric units are DIY-friendly. Whole-house or gas models should always be professionally installed for safety and code compliance. - Is a tankless heater more efficient?
Yes. Both electric and gas models save energy by heating water only when needed—just be sure your electrical system can handle the load.
Conclusion
Knowing how many amps your tankless water heater uses is essential before you buy or install. Electric models draw a lot of power—be sure your panel is up to the task, and always size breakers and wires correctly for safety. Gas models use minimal electricity and are easier to retrofit in homes with smaller panels. Use the charts and advice above to find the right heater for your setup, and enjoy endless, efficient hot water without electrical surprises!