Aquarium Heaters: What Size You Need, by Each Maker's Chart
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Heaters are simple until you try to size one and every chart says something different. Here are the makers' own numbers. Product details are from the listings; we haven't tested them.
Target temperatures
Aqueon: "Bettas, discus and certain other species do best in water that is between 76° and 85° F, most other tropical fish prefer a range of 75° and 80° F, and goldfish do best from 68° to 74° F." Aqueon also warns: "Do not change your aquarium's water temperature suddenly or dramatically."
Sizing: each maker's chart
| Wattage | Aqueon chart | Fluval M Series | EHEIM thermocontrol |
|---|---|---|---|
| 50W | 5-20 gal | Up to 15 gal | 6.6-15.8 gal |
| 100W | 15-40 gal | Up to 30 gal | 26.4-39.6 gal |
| 150W | 30-55 gal | Up to 45 gal | 53-79 gal |
| 200W | 50-75 gal | Up to 65 gal | 79-106 gal |
From Aqueon's wattage guideline PDF, Fluval's M Series page and EHEIM's thermocontrol manual table. Aqueon's general rule is "5 watts per gallon for aquariums 55 gallons or smaller," and it says to size up or add a second heater for a cold room or an exterior wall.
Heaters compared
Aqueon Pro
Adjustable 68 to 88°F with an electronic thermostat accurate to ±1°, shatterproof, and an auto shut-off that resets when it cools, per the listing. Aqueon's page adds it shuts off if tilted top-down.
Aqueon Pro 100W Heater
- For tanks up to 30 gallons (title)
- Adjustable 68-88°F, accurate to ±1°, per the listing
- Shatterproof; auto shut-off if it overheats
EHEIM Jager
Fully submersible with dry-run protection and a TruTemp recalibration dial, per the listing. EHEIM's current thermocontrol line, which retailers sell in the US under the Jager name, lists 18 to 34°C adjustment and ±0.5°C accuracy.
EHEIM Jager 100W Heater
- Fully submersible, per the listing
- Shuts off if the water level drops too low
- TruTemp dial for recalibration
EHEIM Jager 150W Heater
- Fully submersible, per the listing
- Dry-run protection
- TruTemp recalibration dial
Fluval M Series
Borosilicate glass with a reflective finish; Fluval lists settings of 66 to 86°F.
Fluval M 50W Heater
- For tanks up to 15 gallons, per the listing
- Borosilicate glass; reflective finish
- Adjustable dial
Fluval M 150W Heater
- For tanks up to 45 gallons, per the listing
- Borosilicate glass; ceramic heat sink
hygger mini heater (for small tanks)
10W for 1 to 5 gallons, with an external digital controller and shut-off above 95°F or at low water, per the listing.
hygger Mini Betta Heater (10W)
- 10W for 1-5 gallon tanks, per the listing
- 59-93°F range; external digital controller
- Stops heating above 95°F or if water level drops
Use a thermometer
EHEIM builds in a recalibration dial for a reason: a separate thermometer tells you the real temperature.
AQUANEAT Digital Aquarium Thermometer
- Submersible probe with LCD display, per the listing
- Accuracy ±1°C
- Battery included
Safety
- Drip loop: Aqueon says cords should approach the outlet from below so dripping water "will fall off at the upward bend in the cord."
- Wait before plugging in: Aqueon: allow "at least 30 minutes" after installing before plugging in, and unplug and let it cool 30 minutes before removing.
- Placement: Aqueon suggests placing it near the filter outlet for even heat.
FAQ
What size heater?
Use the maker's chart; Aqueon says 5 W/gal up to 55 gal.
Tropical temperature?
75-80°F for most, per Aqueon.
Safe install?
Drip loop, wait 30 minutes before plugging in.