How many watts does a tankless water heater use?
A tankless water heater uses 10,000–27,000 W (about 18,000 W on average). Running 0.5 hours/day, that is about 9.00 kWh a day and 270.0 kWh a month — roughly $49.44 a month at the U.S. average rate of 18.31 ¢/kWh.
This is the tankless water heater electricity usage reference: watts, amps on a 240 V circuit, the kWh math, and links to what that usage costs in each state.
Watts, amps, and kWh for a tankless water heater
| Measure | Value |
|---|---|
| Rated wattage range | 10,000–27,000 W |
| Average draw used in our math | 18,000 W |
| Amps at 240 V | 42–113 A (75 A at the average draw) |
| kWh per hour | 18.00 kWh |
| kWh per day at 0.5 hours/day | 9.00 kWh |
| kWh per month | 270.0 kWh |
| Cost per month at the U.S. average (18.31 ¢/kWh) | $49.44 |
The math is kWh = watts × hours ÷ 1000 and amps = watts ÷ volts. A tankless water heater is normally wired for 240 V in US homes; a 120 V unit of the same wattage would draw twice the amps. For the dollars in your state, open cost to run a tankless water heater in Texas and switch states from there.
Tankless Water Heater electricity usage profile
| Metric | Value |
|---|---|
| kWh per hour | 18.00 kWh |
| kWh per day (typical) | 9.00 kWh |
| kWh per month (typical) | 270.0 kWh |
| kWh per year (typical) | 3285.0 kWh |
| Low runtime scenario | 0.5 hours/day |
| High runtime scenario | 2.5 hours/day |
Connect usage to cost tools
Related appliance usage pages
Source & Method
Source: U.S. Energy Information Administration (EIA) Retail Sales of Electricity. Last dataset period: July 2026. Usage calculations use fixed appliance wattage and runtime assumptions so results stay comparable across pages.
Frequently asked questions
How many watts does a tankless water heater use?
A tankless water heater uses 10,000–27,000 W (about 18,000 W on average). Our usage and cost math uses 18,000 watts running 0.5 hours/day.
How many amps does a tankless water heater draw?
On a 240 V circuit, 10,000–27,000 W works out to about 42–113 A; at the 18,000 W we use in the math that is 75 A.
How much electricity does a tankless water heater use per month?
About 270.0 kWh a month at 0.5 hours/day. Lighter use (0.5 hours/day) comes to roughly 270.0 kWh and heavier use (2.5 hours/day) roughly 1350.0 kWh.
How much does it cost to run a tankless water heater?
About $49.44 a month at the U.S. average rate of 18.31 ¢/kWh — from roughly $34.34 in Louisiana to $129.60 in Hawaii at the same usage. The state cost-to-run pages price it at every state's rate.