How Much Does It Cost to Run an Electric Tankless Water Heater in Hawaii? (2026)
Electric tankless heaters draw enormous power, 12 to 36 kW, but only while hot water is flowing. They avoid the standby losses of a tank, saving 10 to 30 percent for most households, but need heavy wiring.
A typical electric tankless water heater (18,000 W) costs $9.49 per hour, or about $156.58 per month at 0.55 hours a day in Hawaii. Expensive to run
| Wattage | Per hour | Per day | Per month | Per year |
|---|---|---|---|---|
| Low 12,000 W | $6.33 | $5.22 | $156.58 | $1,905 |
| Typical 18,000 W | $9.49 | $5.22 | $156.58 | $1,905 |
| High 36,000 W | $18.98 | $5.22 | $156.58 | $1,905 |
Formula: watts ÷ 1000 × hours × price per kWh. Typical use is 0.55 h/day ≈ 3,614 kWh per year. A more powerful model does the same job faster, so it uses the same energy: the cost per hour changes from row to row, the cost per day does not.
One hour of an electric tankless water heater (18.0 kWh) is the same electricity as
- 6.0dryer loads
- 180kettle boils
- 400hours of a laptop
- 2,000hours of an LED bulb
In Hawaii, with electricity at 52.7¢ per kWh (source: EIA Table 5.6.A, 2026-06), a typical electric tankless water heater costs $9.49 per hour and about $1,905 per year at 0.55 hours a day. That is about 187% more than the national average for the US ($54.47 per month), because electricity in Hawaii costs 52.7¢ per kWh against 18.3¢ nationally. Each $1.00 of electricity buys roughly 0.1 hours of use.
How to lower the cost of running an electric tankless water heater
- Install low-flow showerheads. Flow rate directly drives power draw.
- Fix hot water drips. Each one fires the heater.
- Set the outlet temperature to 49 C and skip mixing cold water at the tap.
In standby it draws about 2 W, which adds roughly 18 kWh ($9.24) per year if it is never unplugged.
Frequently asked questions
How much does a tankless water heater cost per month?
About 300 kWh a month for a family of four, roughly 10 to 30 percent less than a tank.
Do tankless heaters use a lot of electricity?
A lot at once, but for short periods. Total use is typically lower than a tank.
Do I need a panel upgrade for an electric tankless heater?
Often yes. Whole-house units need 100 amps or more of dedicated capacity.
Compare with
Cost by region
US states
- Alabama
- Alaska
- Arizona
- Arkansas
- California
- Colorado
- Connecticut
- Delaware
- District of Columbia
- Florida
- Georgia
- Hawaii
- Idaho
- Illinois
- Indiana
- Iowa
- Kansas
- Kentucky
- Louisiana
- Maine
- Maryland
- Massachusetts
- Michigan
- Minnesota
- Mississippi
- Missouri
- Montana
- Nebraska
- Nevada
- New Hampshire
- New Jersey
- New Mexico
- New York
- North Carolina
- North Dakota
- Ohio
- Oklahoma
- Oregon
- Pennsylvania
- Rhode Island
- South Carolina
- South Dakota
- Tennessee
- Texas
- Utah
- Vermont
- Virginia
- Washington
- West Virginia
- Wisconsin
- Wyoming
Canadian provinces
Related appliances
- Electric Blanket100 W typical
- Heat Pump (Ducted or Mini-Split)2,000 W typical
- Baseboard Heater1,500 W typical
- Portable Fan (Box or Pedestal)50 W typical
Use the generic electricity cost calculator · Which uses more? Take the quiz