Under-tank heater vs. aquarium heater: running cost
An under-tank heater is cheaper to run: about $22 a year versus $47 for an aquarium heater at typical use and 17.99¢/kWh, a $25 difference.
| Under-tank heater | Aquarium heater | |
|---|---|---|
| Typical watts | 20 W | 100 W |
| Watt range | 8–45 W | 25–500 W |
| Typical use | 24 hours a day | 24 hours a day |
| Energy per year | 123 kWh | 263 kWh |
| Cost per hour | 0.3¢ | 0.5¢ |
| Cost per day | 6.0¢ | 13¢ |
| Cost per month | $1.84 | $3.94 |
| Cost per year | $22 | $47 |
| Per year in Hawaii (43.51¢) | $53 | $114 |
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What drives the difference
- Under-tank heater: Heat mats draw 8-40 W continuously, usually on a thermostat.
- Aquarium heater: Heaters cycle with the thermostat; in a 70°F home a heater runs about 25-40% of the time.
Ways to cut either cost
Reptile thermostat
Cycles the mat off when the target temperature is reached.
See options on Amazon Aquarium background insulation
Cuts heat loss through the glass.
See options on AmazonWe may earn a commission from qualifying purchases. It never changes the numbers we show. Disclosure.
Frequently asked questions
Which costs more to run, an under-tank heater or an aquarium heater?
At typical use and the U.S. average rate (17.99¢/kWh), an aquarium heater costs about $47 a year versus $22 for an under-tank heater. That's $25 more, or 2.1× as much.
How many watts do under-tank heater and aquarium heater use?
An under-tank heater typically draws 20 W (range 8–45 W). An aquarium heater draws 100 W (range 25–500 W). Watts alone don't decide cost. Hours of use, cycling and standby matter just as much.
Rates: EIA, 12 months ending 2026-07. Methodology.