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Aquarium heater calculator
Enter the tank size and temperatures to see which heater fits and roughly what heating costs per month.
How it is calculated
Heater wattage = litres × temperature difference × factor. The factor describes how much heat the tank loses: 0.1 W per litre and degree with a lid in a normal room, 0.15 W for an open tank, draughts or a basement.
Example: 200 litres, room 19 °C, water 25 °C, with a lid: 200 × 6 × 0.1 = 120 W. Heaters come in fixed sizes, so the calculator picks the next one up (150 W here). A little headroom is intended: a stronger heater runs for shorter periods, it does not cost more.
What matters is the coldest room temperature, for example at night in winter or while airing the room. Do not use the temperature of a warm afternoon.
Cutting the electricity cost
- Lid or glass cover: an open tank loses a lot of heat through evaporation.
- No warmer than needed: 24 to 25 °C is enough for most tropical fish. With the water 6 degrees above the room, every degree less saves about a sixth of the heating cost.
- Location: not against a cold outside wall or in a window, and not right above a radiator either, where the temperature swings a lot.
- Shrimp and cold-water species: Neocaridina shrimp, white cloud minnows or goldfish usually need no heater in a normally heated home.
In the app: equipment and temperature at a glance
In Aqualizer you add your heater with the tank. The planner estimates the electricity cost for your country, and the temperature of your readings is checked against the animals in your tank.
- Heater, filter and light per tank
- Temperature matched to your animals
- Running costs in the tank planner
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Aquarium heater FAQ
How many watts does an aquarium heater need?
As a rule of thumb 0.1 W per litre and degree of difference between room and water, with a lid. For 100 litres with a 20 °C room and 25 °C water that is 50 W. In a cold room or with an open top, about one and a half times as much.
Is an oversized heater a problem?
Not as long as the thermostat works: it just switches on for shorter periods. If a heater sticks on, however, a big one heats the tank faster. That is why two smaller heaters are better from about 200 litres.
What does an aquarium heater cost per month?
Less than the wattage suggests, because it only heats part of the time. A 100-litre tank with a lid, 4 degrees above room temperature, uses about 17 kWh per month, roughly €5 at €0.29 per kWh.
Do shrimp need a heater?
Neocaridina shrimp (e.g. red cherry) are comfortable at 20 to 26 °C and usually need none in a heated home. Caridina species such as crystal shrimp prefer a steady 22 to 24 °C.
Where do I place the heater in the tank?
Where the water flows well, for example near the filter outlet or intake. That spreads the heat evenly. The heater must be submerged as deep as the manufacturer states.