How much does an aquarium heater cost to run?

Heater cost calculator

What if the duty cycle dropped to (%) You'd save .

Formula: kWh/month = watts × 24 × duty ÷ 100 × 30.44 ÷ 1000. The example rate is close to the US average residential price of 18.31¢/kWh for July 2026 (Colorado: 17.00¢), from the EIA Electric Power Monthly, Table 5.6.A. Use the rate on your own bill. The 30% example duty cycle sits inside the 20–40% range ReefKalk gives for heaters in a heated room (source).

How to find your real duty cycle

Plug the heater into a plug-in energy meter or a smart plug that reports energy use for a few days, then divide the kWh it used by what it would use running nonstop (watts × 24 × days ÷ 1000). Many aquarium controllers also log heater on-time. Duty cycle changes with the seasons, so a winter reading will be higher than a summer one.

Ways to cut heater cost

• Cover the top where you safely can. Evaporation carries heat out of the water, so a lid or partial cover means the heater has less to replace. Leave room for gas exchange and keep covers clear of lights.
• Mind the room. The heater only makes up the gap between room and tank temperature. A tank against an outside wall, near a drafty window or in a cold basement works harder.
• Count the heat you already pay for. Pumps and lights warm the water too. That's why heaters often run less than you'd expect, and why turning off a pump can raise heater run time.
• Bigger isn't more expensive, just riskier. At a steady temperature the energy used is set by heat loss, so an oversized heater runs in shorter bursts for roughly the same kWh. The real cost of oversizing is the damage if it sticks on, which is why a separate temperature controller is worth considering.
• Measure before you buy anything. Get the duty cycle first, then use the calculator above to see whether a change is worth its price.

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