A tankless water heater typically uses between 15 to 30 kilowatts per hour when in operation, depending on the model and the temperature rise needed, making it more energy-efficient than traditional tank heaters by only heating water on demand.
Tankless water heaters use 8-28 kW per hour during operation, with monthly consumption ranging from 20-50 kWh for most households. While they draw more power when active, their on-demand operation makes them 17-40% more efficient than traditional tank heaters.
How Much Electricity Does a Tankless Water Heater Use?
Electric tankless water heaters consume power only when hot water is demanded. Their electricity usage depends on three key factors:
- Flow rate: More gallons per minute (GPM) requires more power
- Temperature rise: The difference between incoming and desired water temperature
- Usage patterns: Frequency and duration of hot water use
Typical Power Consumption
| Heater Size | Power Draw | Flow Rate | Best For |
|---|---|---|---|
| Small (point-of-use) | 3-8 kW | 0.5-2 GPM | Single faucet |
| Medium | 18-24 kW | 3-5 GPM | 1-2 bathroom home |
| Large | 27-36 kW | 6-8 GPM | Whole house |
Monthly Electricity Costs
A family of four typically uses about 50 gallons of hot water daily. With an 18 kW unit operating at half capacity:
- Daily: 9 kWh ($1.35 at $0.15/kWh)
- Monthly: 270 kWh ($40)
- Yearly: 3,285 kWh ($493)
Compare this to traditional tank heaters that maintain water temperature 24/7.
Tankless vs. Traditional Water Heater Electricity Use
While tankless models draw more power when active, they operate for shorter durations:
Key Differences
- Standby losses: Tank heaters lose 1-2% of heat hourly
- Recovery time: Tankless provides endless hot water
- Peak demand: Tankless requires higher amperage circuits
According to the U.S. Department of Energy, tankless heaters can be 24-34% more efficient for homes using 41 gallons or less daily.
Gas vs. Electric Tankless Water Heaters
Gas models use minimal electricity (25-65 watts during operation) but have other considerations:
Electric Tankless
- Higher efficiency (98% vs 80-85% for gas)
- No venting required
- May need electrical panel upgrade
Gas Tankless
- Lower operating costs in most areas
- Requires gas line and proper venting
- Needs annual maintenance
For those considering gas options, our guide on propane tankless water heaters provides detailed comparisons.
Factors Affecting Electricity Consumption
Climate and Water Temperature
Groundwater in northern states can be 20°F colder than southern states, requiring more energy to heat.
Household Size
A single person might use just 10-15 gallons daily, while a family of five could use 75+ gallons.
Usage Patterns
Simultaneous showers, appliances running, and peak demand periods affect consumption.
Installation Considerations
Electric tankless heaters often require:
- 240V circuit (some need multiple 40-50A breakers)
- Proper wire gauge (typically 6-8 AWG)
- Possible service panel upgrade
The MRCOOL study found installation costs averaging $510 but varying by home requirements.
Maximizing Efficiency
Temperature Settings
Set to 120°F (49°C) for optimal efficiency and safety. Each 10°F reduction saves 3-5% on energy.
Flow Restrictors
Low-flow showerheads (1.5-2.0 GPM) reduce demand on the heater.
Maintenance
Annual descaling (especially in hard water areas) maintains efficiency. Consider a water filter to prevent mineral buildup.
Alternative Options
For those concerned about electricity use:
- Heat pump water heaters: 2-3x more efficient than resistance heating
- Hybrid systems: Combine tankless with solar pre-heating
- Point-of-use heaters: Small units at each faucet reduce pipe heat loss
