Aquarium heaters
For a tropical tank, choose an adjustable, fully submersible heater of about 3 to 5 watts per gallon, using the higher figure when the water needs to sit about 10°F above your coldest room temperature. For extra safety, run it through an external temperature controller so a stuck heater can't cook the tank. Cold-water animals like goldfish and axolotls don't need a heater.
Which heater does what
- Fully Submersible Glass HeaterVersatile, adjustable internal tank heatingUse for standard freshwater or marine tanks where you want to set the temperature and place the heater flexibly.Amazon ↗
- Titanium Heater with ControllerShatterproof durability for large aquariumsUse in tanks with large, boisterous fish or turtles that could break glass. Most titanium heaters are bare elements and must run through a separate controller.Amazon ↗
- Inline HeaterOut-of-sight plumbing-integrated heatingUse on the return tubing of a canister filter to keep equipment out of the main display tank.Amazon ↗
- Preset HeaterFixed temperature, usually about 78°FFine for small tropical tanks in rooms that stay fairly steady. You can't adjust it, so check the water with a thermometer, and don't use one where you need a lower or higher temperature.Amazon ↗
Sizing: Plan for about 3 to 5 watts per gallon of actual water, using 5 watts per gallon when the water needs to sit about 10°F above room temperature (for example, about 100 watts for a 20-gallon tank). If the room can drop 15°F or more below your target, size up or split the load across two heaters.
What each animal's guide calls for
From the checklists on each care guide, so this table and those pages always agree.
- Betta fish25W adjustable aquarium heater78–80°F water$12–$22
- Red-eared sliderSubmersible Water Heater75–80°F water$25–$55
- AxolotlAquarium Water Chiller or Cooling Fan60–68°F water$20–$180
- Freshwater shrimpSubmersible Preset Heater68–78°F water$12–$25
- Neon tetra100W Submersible Aquarium Heater72–78°F water$20–$35
- GuppySubmersible Aquarium Heater (50W)72–82°F water$12–$25
- Mystery snailSubmersible Aquarium Heater 25W70–78°F water$10–$20
- Angelfish100W Submersible Glass Heater76–82°F water$18–$35
- Musk turtleSubmersible Heater with Guard72–80°F water$20–$40
- Bristlenose plecoSubmersible Aquarium Heater73–80°F water$15–$30
- African dwarf frogSubmersible Aquarium Heater 50W72–78°F water$12–$25
How to choose
- 01Work out your real water volume and temperature liftAllow for water displaced by substrate and decor, then subtract your coldest room temperature from your target water temperature. The bigger the gap, the more watts you need.
- 02Choose titanium elements for large or aggressive speciesLarge cichlids, catfish, or turtles can easily strike and shatter glass heaters, causing fatal shock hazards.
- 03Install a protective heater guard for burn-prone animalsTurtles, plecos, snails and scaleless fish often rest against heaters and can be burned.
- 04Add an external temperature controller as a failsafeA heater's built-in thermostat can stick in the on position. A separate controller with its own probe cuts power if the water gets too warm.
- 05Split total wattage between two heaters on tanks over 50 gallonsTwo smaller heaters mean one stuck heater is less likely to overheat the tank, and the other keeps some heat going if one fails.
Common mistakes
- Plugging in a new glass heater immediately. Let it sit in the water for 15 to 30 minutes first so the glass can adjust to the water temperature.
- Leaving a heater powered on during water changes. A heater running out of water can crack or melt.
- Heating cold-water animals like axolotls or goldfish to tropical temperatures. Warm water holds less oxygen and stresses them, and axolotls suffer above about 70°F.
- Placing the heater in a dead zone with poor water circulation: Weak flow causes local hot spots around the heater while leaving the rest of the tank cold.
- Trusting the heater's dial. Settings are often off by a few degrees, so check with a separate thermometer.
Questions people ask
Which animals must NOT have an aquarium heater?
Cold-water species such as axolotls, goldfish and white cloud mountain minnows don't need a heater in a normal indoor room. Axolotls need water between 60°F and 68°F, and temperatures above 70°F cause stress, fungal infections and death. Always check your species' care needs before adding heat.
Why should I use two heaters instead of one on large tanks?
On tanks of about 50 gallons and up, splitting the wattage across two heaters spreads heat more evenly and adds backup. If one fails off, the other keeps some warmth. If one sticks on, it heats the tank more slowly than a single large heater would.
Why is an external temperature controller recommended?
A common cause of tank disasters is a heater's thermostat sticking in the 'on' position. An external controller powers the heater through its own probe and cuts the electricity if the water passes your set point.
Where is the best place to position an aquarium heater?
Place it near the filter outlet or another area of strong flow, angled at about 45 degrees if it's a long tube heater, and keep it below the maker's minimum water line. Put a thermometer on the far side of the tank to check the heat is reaching everywhere.
What is the difference between glass and titanium aquarium heaters?
Glass heaters are inexpensive, all-in-one units, but they can crack from a knock or from running out of water. Titanium heaters are shatterproof and good for large, rough fish and turtles, but most are bare elements that need a separate controller.