Aqueon’s heater chart sizes a heater by the tank and by how far the water has to rise above the room, so a 20 gallon tank heated 10 °F above the room takes 100 watts. Most other makers rate their heaters by tank size alone.
Set the water to the temperature your fish need. Aqueon bases its chart on a room at 68 to 72 °F.
Heater size
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When the makers disagree
The charts don’t always match. Tetra’s 29 gallon kit comes with a 200 watt heater, while Aqueon’s chart puts a 30 gallon tank at 100 to 150 watts and Marineland rates its 100 watt heater for up to 29 gallons. Each figure is for that maker’s own heater, so go by the rating for the heater you have.
Some heaters can’t be set. Tetra’s HT heaters hold the water at 78 °F, while EHEIM’s thermocontrol heaters can be set from 18 to 34 °C.
EHEIM’s ratings and the conditions they’re for
EHEIM’s manual for its thermocontrol heaters calls these standard ratings for closed aquariums in a 21 °C (70 °F) room, with water up to 26 °C (79 °F).
| Type | Watts | Liters | US gallons |
|---|---|---|---|
| 3611 | 25 | 20–25 | 5.2–6.5 |
| 3612 | 50 | 25–60 | 6.6–15.8 |
| 3613 | 75 | 60–100 | 15.8–26.4 |
| 3614 | 100 | 100–150 | 26.4–39.6 |
| 3615 | 125 | 150–200 | 39.6–53 |
| 3616 | 150 | 200–300 | 53–79 |
| 3617 | 200 | 300–400 | 79–106 |
| 3618 | 250 | 400–600 | 106–159 |
| 3619 | 300 | 600–1000 | 159–260 |
The manual heads the table 230–240 V, with the 120 V types in brackets, and gives one set of figures. Gallons are EHEIM’s own.
Does my tank need a heater?
Tropical fish need a heater set to the right temperature for the species, and goldfish, kept at 10 to 21 °C, normally don’t. Every heater must be controlled by a thermostat, and heaters are available with one built in.
What the heater manuals say about safety
The Aqueon, Marineland and EHEIM manuals all say to unplug the heater before you work in the tank, and never to run it out of the water. They differ on how long to let it cool before you lift it out, so follow the manual for your own heater.
| Maker | Its manual says |
|---|---|
| Aqueon | “ALWAYS disconnect all immersed electrical equipment from power source before placing hands in water.” “DO NOT operate or leave product plugged-in when outside of water.” “Make sure that the appliance is submerged at least to the minimum water level line.” |
| Marineland | “Always disconnect the heater before performing water changes.” “Always allow your heater to cool for at least 15 minutes after unplugging and before removal from water.” “Wait at least 15 minutes before plugging in your heater.” |
| EHEIM | “After disconnection from the mains, the appliance must be left in the water for 30 minutes in order to cool down.” “Prior to the initial operation of the heater, place it in the water of your aquarium for 20-30 minutes without turning it on.” “If you have accidentally removed the heater during operation: Do not submerge the heater back into the water. Do not touch any hot surfaces. Remove the mains plug and allow the heater to cool down for at least one hour on a heat-resistant base.” |