Wondering how much power an electric tankless water heater really uses—and how it impacts your monthly bill? You’re not alone! Tankless heaters are famously efficient, but they demand serious amps when heating water. Whether you’re planning an upgrade, comparing costs, or just want to avoid surprises, this guide will break down exactly how much electricity a tankless water heater uses, with examples, tips to save, and top product picks for every household.
Quick Answer: Typical Electricity Use for Tankless Water Heaters
- Whole-House Electric Tankless: Draws 18,000 to 36,000 watts (18–36 kW) when running at full power. Most require 60–150 amps at 240V—much higher than a standard appliance.
- Point-of-Use Models: Use 3,000 to 13,000 watts (3–13 kW), requiring a 20–60 amp breaker.
- Monthly Cost: For a family of four, expect to use 300–500 kWh/month for hot water only, costing $45–$75 per month at a $0.15/kWh rate.
How to Calculate Electricity Usage (and Cost) for Your Tankless Water Heater
- Find the Power Rating: Check your heater’s kW rating (e.g., 24 kW, 27 kW, 36 kW).
- Estimate Daily Use: Most families run hot water for about 1 to 2 hours total per day (all showers, laundry, and dishes combined).
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Monthly kWh Calculation:
- Example: 24 kW x 1.5 hours/day x 30 days = 1,080 kWh/month
- In reality, heaters rarely run at full power the whole time—so real-world use is usually about one-third to half the max.
- So, expect 300–500 kWh/month for a typical household.
- Cost to Run: Multiply kWh x your local rate (e.g., 400 kWh x $0.15 = $60/month for hot water).
What Affects Electricity Use in a Tankless Water Heater?
- Number of People/Hot Water Fixtures: More hot water means more power needed.
- Unit Size (kW Rating): Bigger heaters use more power, but deliver more hot water at once.
- Incoming Water Temperature: Colder groundwater = heater must work harder to reach your set temp.
- Temperature Setting: Higher set temps increase electricity use. 120°F is ideal for most homes.
- Usage Patterns: Back-to-back showers or laundry/dishes at once increase power draw.
- Efficiency (UEF): High-efficiency models deliver more hot water per kWh.
Do I Need to Upgrade My Electrical Panel?
- Most whole-house electric tankless heaters need 100–150 amps of dedicated service.
- If you have a 200-amp panel and not too many other big appliances, you’re usually fine. For older 100-amp panels, upgrades are often required.
- Each heating element may require its own 40–60 amp breaker and #6 or #8 wire.
- Always check with a licensed electrician before purchasing and installing a high-power tankless unit.
Buyer’s Guide: Choosing the Right Electric Tankless Water Heater
- Power Rating (kW): Match your max GPM needs (see our full sizing guide).
- Amps & Voltage: Know your panel’s capacity—never overload!
- Efficiency: Higher UEF (Uniform Energy Factor) means bigger savings.
- Controls: Digital displays and thermostatic controls help save power.
- Warranty & Brand: Stick with trusted brands for longer life and easier support.
- Professional Install: Big electric tankless heaters should always be installed by a licensed electrician for safety and code compliance.
Top Electric Tankless Water Heaters: Reviewed
EcoSmart ECO 27 Electric Tankless Water Heater
- 27 kW, 112.5 amps at 240V (needs 3 x 40A breakers)
- 6.5 GPM (warm climates), 3.5–4.0 GPM in colder regions
- Digital temp control, lifetime warranty for residential use
- Estimated monthly cost: $40–$70 (typical family)
Final Verdict: Most popular and versatile electric tankless heater—great for families in warm to moderate climates.
See it on Amazon
Rheem RTEX-24 Electric Tankless Water Heater
- 24 kW, 100 amps at 240V (needs 2 x 50A breakers)
- 5.9 GPM (warm), 2.5–3.5 GPM (cold climates)
- Simple digital thermostat and easy install
- Estimated monthly cost: $35–$65 (typical use)
Final Verdict: Reliable, affordable, and easy to use—perfect for smaller homes or apartments.
Check price on Amazon
Stiebel Eltron Tempra 36 Plus Electric Tankless Water Heater
- 36 kW, 150 amps at 240V (needs 3 x 50A breakers)
- 7.5 GPM (warm), 4.0–5.0 GPM (cold)
- Advanced flow control and digital display
- Estimated monthly cost: $60–$90 (large family, high use)
Final Verdict: Maximum power for big homes or simultaneous multi-fixture use.
See details on Amazon
Comparison Table: Electric Tankless Water Heater Power Usage
Model | Power (kW) | Amps @ 240V | Max GPM | Estimated Monthly Cost | Best For | Price Link |
---|---|---|---|---|---|---|
EcoSmart ECO 27 | 27 | 112.5 | 6.5 | $40–$70 | Most homes | View |
Rheem RTEX-24 | 24 | 100 | 5.9 | $35–$65 | Smaller homes | View |
Stiebel Tempra 36 Plus | 36 | 150 | 7.5 | $60–$90 | Large families | View |
How to Save Electricity With a Tankless Water Heater
- Set Temperature to 120°F: Lower temps use less power—enough for comfort and safety.
- Install Low-Flow Fixtures: Showerheads and aerators with 1.5–2.0 GPM ratings cut demand.
- Fix Leaks Fast: Even a small drip wastes hot water and power over time.
- Schedule Showers & Appliances: Avoid running too many hot water appliances at once.
- Perform Regular Maintenance: Descale yearly in hard water areas for peak efficiency.
FAQ: Electricity Use for Tankless Water Heaters
- Do tankless water heaters use electricity when off?
Electric units use almost zero standby power—just a tiny amount for electronics. Power is only used while heating water. - How much does it cost per month to run?
For a family of four, plan on $40–$80/month depending on use and electricity rates. - Can my existing panel handle a tankless heater?
Check your panel size and how many other major appliances are in use. Most big tankless units need 100–150A available. - Are electric tankless units more efficient than tank models?
Yes, especially when installed close to where hot water is needed. No standby heat loss! - Is installation DIY-friendly?
Small point-of-use units can be DIY. Whole-house models should be professionally installed for safety and code compliance.
Conclusion
Electric tankless water heaters are efficient, powerful, and space-saving—but require careful planning for your home’s electrical system. Use the tips, examples, and product picks above to choose the best model and get the most value for your energy dollar. Have questions about sizing, wiring, or saving on your electric bill? Just ask below and enjoy endless, efficient hot water!