How much does it cost to run an under-tank heater?
An under-tank heater costs about 0.3¢ per hour, 6.0¢ a day, $1.84 a month and $22 a year at typical use (24 hours a day) and the U.S. average rate of 17.99¢/kWh. Heat mats draw 8-40 W continuously, usually on a thermostat.
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Cost by hours of use
| Hours per day | kWh/day | Per day | Per month | Per year (all year) |
|---|---|---|---|---|
| 1 hour | 0.01 | 0.3¢ | $0.08 | $1 |
| 2 hours | 0.03 | 0.5¢ | $0.15 | $2 |
| 4 hours | 0.06 | 1.0¢ | $0.31 | $4 |
| 8 hours | 0.11 | 2.0¢ | $0.61 | $7 |
| 12 hours | 0.17 | 3.0¢ | $0.92 | $11 |
| 24 hours | 0.34 | 6.0¢ | $1.84 | $22 |
Cost to run an under-tank heater in every state
The same under-tank heater costs $15 a year in North Dakota and $53 in Hawaii, at each state's average residential rate (12 months ending July 2026).
| State | Rate | Per hour | Per month | Per year |
|---|---|---|---|---|
| North Dakota | 12.32¢ | 0.2¢ | $1.26 | $15 |
| Idaho | 12.65¢ | 0.2¢ | $1.29 | $16 |
| Nebraska | 12.86¢ | 0.2¢ | $1.32 | $16 |
| Louisiana | 12.99¢ | 0.2¢ | $1.33 | $16 |
| Utah | 13.32¢ | 0.2¢ | $1.36 | $16 |
| Nevada | 13.36¢ | 0.2¢ | $1.37 | $16 |
| Arkansas | 13.43¢ | 0.2¢ | $1.37 | $16 |
| Tennessee | 13.56¢ | 0.2¢ | $1.39 | $17 |
| Oklahoma | 13.70¢ | 0.2¢ | $1.40 | $17 |
| Montana | 13.84¢ | 0.2¢ | $1.42 | $17 |
| Kentucky | 13.92¢ | 0.2¢ | $1.42 | $17 |
| Missouri | 13.95¢ | 0.2¢ | $1.43 | $17 |
| Wyoming | 14.01¢ | 0.2¢ | $1.43 | $17 |
| Washington | 14.12¢ | 0.2¢ | $1.44 | $17 |
| Iowa | 14.13¢ | 0.2¢ | $1.45 | $17 |
| South Dakota | 14.20¢ | 0.2¢ | $1.45 | $17 |
| Mississippi | 14.77¢ | 0.2¢ | $1.51 | $18 |
| North Carolina | 14.77¢ | 0.2¢ | $1.51 | $18 |
| Kansas | 15.09¢ | 0.2¢ | $1.54 | $19 |
| Georgia | 15.12¢ | 0.2¢ | $1.55 | $19 |
| New Mexico | 15.32¢ | 0.2¢ | $1.57 | $19 |
| Florida | 15.39¢ | 0.2¢ | $1.57 | $19 |
| Arizona | 15.40¢ | 0.2¢ | $1.57 | $19 |
| West Virginia | 15.48¢ | 0.2¢ | $1.58 | $19 |
| Oregon | 15.50¢ | 0.2¢ | $1.59 | $19 |
| South Carolina | 15.64¢ | 0.2¢ | $1.60 | $19 |
| Texas | 15.96¢ | 0.2¢ | $1.63 | $20 |
| Minnesota | 16.22¢ | 0.2¢ | $1.66 | $20 |
| Alabama | 16.44¢ | 0.2¢ | $1.68 | $20 |
| Virginia | 16.48¢ | 0.2¢ | $1.69 | $20 |
| Colorado | 16.58¢ | 0.2¢ | $1.70 | $20 |
| Indiana | 16.94¢ | 0.2¢ | $1.73 | $21 |
| Delaware | 17.79¢ | 0.2¢ | $1.82 | $22 |
| Ohio | 18.25¢ | 0.3¢ | $1.87 | $22 |
| Wisconsin | 18.74¢ | 0.3¢ | $1.92 | $23 |
| Illinois | 18.79¢ | 0.3¢ | $1.92 | $23 |
| Pennsylvania | 20.70¢ | 0.3¢ | $2.12 | $25 |
| Maryland | 21.03¢ | 0.3¢ | $2.15 | $26 |
| Michigan | 21.05¢ | 0.3¢ | $2.15 | $26 |
| New Jersey | 23.78¢ | 0.3¢ | $2.43 | $29 |
| Vermont | 23.80¢ | 0.3¢ | $2.43 | $29 |
| District of Columbia | 24.20¢ | 0.3¢ | $2.47 | $30 |
| New Hampshire | 26.67¢ | 0.4¢ | $2.73 | $33 |
| Alaska | 26.85¢ | 0.4¢ | $2.75 | $33 |
| Connecticut | 27.99¢ | 0.4¢ | $2.86 | $34 |
| New York | 28.39¢ | 0.4¢ | $2.90 | $35 |
| Rhode Island | 29.27¢ | 0.4¢ | $2.99 | $36 |
| Maine | 29.31¢ | 0.4¢ | $3.00 | $36 |
| Massachusetts | 30.43¢ | 0.4¢ | $3.11 | $37 |
| California | 32.99¢ | 0.5¢ | $3.37 | $40 |
| Hawaii | 43.51¢ | 0.6¢ | $4.45 | $53 |
How to cut the cost
- Always use a thermostat; it cuts power use and prevents burns.
- Size the mat to one-third of the tank floor.
- Keep the enclosure in a warm room.
Cheaper ways to get the job done
Cycles the mat off when the target temperature is reached.
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Compare with similar appliances
| Appliance | Watts | Typical use | Per month | Per year |
|---|---|---|---|---|
| Under-tank heater | 20 | 24 hours a day | $1.84 | $22 |
| Reptile heat lamp | 100 | 12 hours a day | $6.57 | $79 |
| Aquarium heater | 100 | 24 hours a day | $3.94 | $47 |
| Heated pet bed | 6 | 24 hours a day for 7 months a year | $0.79 | $6 |
| Aquarium | 135 | 24 hours a day | $6.39 | $77 |
| Pet water fountain | 2 | 24 hours a day | $0.26 | $3 |
Head-to-head comparisons
Frequently asked questions
How much does it cost to run an under-tank heater per hour?
An under-tank heater drawing 20 watts uses 0.01 kWh per hour while running (70% duty cycle). At the U.S. average of 17.99¢/kWh that's 0.3¢ per hour. In North Dakota (12.32¢) it's 0.2¢. In Hawaii (43.51¢) it's 0.6¢.
How much does it cost to run an under-tank heater per month?
At typical use (24 hours a day), an under-tank heater costs about $1.84 a month and $22 a year, at the U.S. average rate. Enter your ZIP in the calculator above for your utility's rate.
How many watts does an under-tank heater use?
Most under-tank heaters use 8 to 45 watts. Check the label on the back or bottom for your model's exact rating.
How many kWh does an under-tank heater use?
About 0.34 kWh a day and 123 kWh a year at typical use (24 hours a day).
Does an under-tank heater use a lot of electricity?
No. At about 123 kWh a year it's a small share (1.2%) of the average U.S. home's 10,492 kWh.
Is it cheaper to run an under-tank heater or a reptile heat lamp?
At typical use, an under-tank heater costs about $22 a year versus $79 for a reptile heat lamp. So the under-tank heater is cheaper by about $57 a year. Use the comparison table above to compare them at your own settings.
How can I lower the cost of running an under-tank heater?
- Always use a thermostat; it cuts power use and prevents burns.
- Size the mat to one-third of the tank floor.
- Keep the enclosure in a warm room.
Rates updated 2026-10-21: EIA data through July 2026. Typical wattage and usage reviewed against DOE, ENERGY STAR and manufacturer specs. Methodology.