Sized for a 20 gallon tank
| Model | Rated for | Power | Length |
|---|---|---|---|
| Aqueon Pro 50 Adjustable, electronic · Its 50 W is under the 100 W both charts give, so it may not hold 78 °F unless the room stays warmer than 70 °F. | Up to 20 gal | 50 W | 9 in |
| Aqueon Submersible Glass Heater 50 W Adjustable submersible · Its 50 W is under the 100 W both charts give, so it may not hold 78 °F unless the room stays warmer than 70 °F. | Up to 20 gal | 50 W | 8.75 in |
| hygger Precise Aquarium Heater 100W Adjustable, electronic | 10–20 gal | 100 W | 5.9 in |
| hygger Titanium Tube Heater 100W Adjustable, electronic | 15–20 gal | 100 W | 7.09 in |
| Aqueon Preset Heater 50 W Preset · Its 50 W is under the 100 W both charts give, so it may not hold 78 °F unless the room stays warmer than 70 °F. | Up to 20 gal | 50 W | Not published |
| EHEIM thermocontrol 75 Adjustable submersible · Its 75 W is under the 100 W both charts give, so it may not hold 78 °F unless the room stays warmer than 70 °F. | 15.8–26.4 gal | 75 W | 10.6 in |
| Cobalt Aquatics Neo-Therm Pro 100W Adjustable, electronic | Up to 29 gal | 100 W | 9.75 in |
| Fluval E100 Adjustable, electronic | Up to 30 gal | 100 W | 11.75 in |
| Fluval M100 Adjustable submersible | Up to 30 gal | 100 W | 11 in |
| Aqueon Preset Heater 100 W Preset | Up to 30 gal | 100 W | Not published |
| Tetra HT30 Preset | 10–30 gal | 100 W | Not published |
| Aqueon Pro 100 Adjustable, electronic | 15–40 gal | 100 W | 10.5 in |
| Aqueon Submersible Glass Heater 100 W Adjustable submersible | Up to 40 gal | 100 W | 10.325 in |
| hygger Precise Aquarium Heater 200W Adjustable, electronic | 20–40 gal | 200 W | 9.25 in |
| Fluval M150 Adjustable submersible | Up to 45 gal | 150 W | 13 in |
| Aqueon Pro 150 Adjustable, electronic | Up to 55 gal | 150 W | 12.75 in |
| Aqueon Submersible Glass Heater 150 W Adjustable submersible | Up to 55 gal | 150 W | 11.875 in |
| Aqueon Preset Heater 150 W Preset | Up to 55 gal | 150 W | Not published |
| Fluval E200 Adjustable, electronic | Up to 65 gal | 200 W | 14 in |
| Fluval M200 Adjustable submersible | Up to 65 gal | 200 W | 13 in |
| Aqueon Pro 200 Adjustable, electronic | Up to 75 gal | 200 W | 12.75 in |
| Aqueon Submersible Glass Heater 200 W Adjustable submersible | Up to 75 gal | 200 W | 13 in |
| Aqueon Preset Heater 200 W Preset | Up to 75 gal | 200 W | Not published |
The charts are for an average room. In a colder room, or a tank without a lid, work out your own figure in the heater size calculator; for a warmer one, the smaller heaters here are enough.
Rated for it, but more than it needs
These cover 20 gallons, but they are much more powerful than the makers’ charts ask for. If its thermostat sticks on, an oversized heater overheats the water faster.
- Fluval M300: Rated up to 80 gal, but its 300 W is more than twice the 100 W the makers’ charts give for 20 gallons.
- Aqueon Pro 300: Rated up to 100 gal, but its 300 W is more than twice the 100 W the makers’ charts give for 20 gallons.
- Aqueon Submersible Glass Heater 300 W: Rated up to 100 gal, but its 300 W is more than twice the 100 W the makers’ charts give for 20 gallons.
- Fluval E300: Rated up to 100 gal, but its 300 W is more than twice the 100 W the makers’ charts give for 20 gallons.
Not for a 20 gallon tank
- hygger Digital Mini Heater 15W: Rated 0.4–2.64 gal: too small for 20 gallons.
- Aqueon Aquatic Flat Heater 7.5 W: Rated 1–3 gal: too small for 20 gallons.
- hygger Digital Mini Heater 25W: Rated 0.4–5.3 gal: too small for 20 gallons.
- EHEIM thermocontrol 25: Rated 5.2–6.6 gal: too small for 20 gallons.
- Aqueon Aquatic Flat Heater 15 W: Rated 5–10 gal: too small for 20 gallons.
- hygger Precise Aquarium Heater 50W: Rated 5–10 gal: too small for 20 gallons.
- Tetra HT10: Rated 2–10 gal: too small for 20 gallons.
- hygger Digital Mini Heater 50W: Rated 0.4–11.9 gal: too small for 20 gallons.
- Fluval M50: Rated up to 15 gal: too small for 20 gallons.
- hygger Titanium Tube Heater 50W: Rated 10–15 gal: too small for 20 gallons.
- EHEIM thermocontrol 50: Rated 6.6–15.8 gal: too small for 20 gallons.
- hygger Digital Mini Heater 75W: Rated 0.4–15.9 gal: too small for 20 gallons.
- EHEIM thermocontrol 100: Rated 26.4–39.6 gal: built for bigger tanks than 20 gallons.
- hygger Titanium Tube Heater 200W: Rated 30–40 gal: built for bigger tanks than 20 gallons.
- Tetra HT40: Rated 30–40 gal: built for bigger tanks than 20 gallons.
- EHEIM thermocontrol 125: Rated 39.6–53 gal: built for bigger tanks than 20 gallons.
- Tetra HT55: Rated 40–55 gal: built for bigger tanks than 20 gallons.
- hygger Precise Aquarium Heater 300W: Rated 40–60 gal: built for bigger tanks than 20 gallons.
- hygger Titanium Tube Heater 300W: Rated 50–60 gal: built for bigger tanks than 20 gallons.
- EHEIM thermocontrol 150: Rated 53–79 gal: built for bigger tanks than 20 gallons.
- hygger Titanium Tube Heater 500W: Rated 70–80 gal: built for bigger tanks than 20 gallons.
- hygger Precise Aquarium Heater 500W: Rated 55–100 gal: built for bigger tanks than 20 gallons.
- EHEIM thermocontrol 200: Rated 79–106 gal: built for bigger tanks than 20 gallons.
- EHEIM thermocontrol 250: Rated 106–159 gal: built for bigger tanks than 20 gallons.
- EHEIM thermocontrol 300: Rated 159–264 gal: built for bigger tanks than 20 gallons.
Before you choose
Put the heater where the filter’s flow passes it, so the warmth spreads, and check the temperature with a separate thermometer. How to size and place a heater.
Tank pages: 20 gallon long · 20 gallon high · Filters for a 20 gallon tank →