We independently research, test, review, and recommend the best products—learn more about our process. If you buy something through our links, we may earn a commission.
Whether you’re investing in your first aquarium or looking to give your current school a fin-tastic new home, an aquarium heater should be on your list of supplies. When selecting the best heater, you’ll want to consider what type and how many fish will be living in your aquarium, how large the tank is, and where you should place the heater. We researched the best submersible aquarium heaters with all of those factors in mind.
Here are the best submersible aquarium heaters for happy, healthy aquatic pets.
Best Overall: FREESEA Aquarium Heater Fish Tank Submersible Heater
Thanks to this heater’s real time temperature displayed in large, easy-to-read LED, you won’t have to buy a separate thermometer. Better yet, you gain peace of mind that your tank is always the right temperature because the heater will automatically turn on if the tank water drops below your set temperature. This heater can also be installed on the side or bottom of your tank for flexibility when designing your aquarium.
This fully submersible thermometer can heat the water in a tank from one to 10 gallons anywhere from 59 to 94 degrees Fahrenheit, making it a smart choice for saltwater or freshwater fish. The heating function automatically kicks on and off as needed, and you control the temperature via a touch button on the cord. Be sure to avoid submerging the cord underwater as this portion of the heater is not waterproof. Turn the power off on the heater at least 10 minutes before cleaning or changing the water in your fish tank.
Best for Large Tanks: Orlushy Submersible Aquarium Heater, 500W
Large tanks require stronger heaters, and this 500-watt unit can keep tanks up to 100 gallons in a fish-safe range of 68 to 89 degrees. It’s 13 inches long and does need to be fully submerged in water to work. If your tank isn’t that deep, consider buying two smaller heaters, something experts recommend for a more even distribution of heat (you’ll want to place the heaters on opposite ends of the tank). You set the heat via a temperature control knob on the heater and can tell that it’s working by the red indicator light. It has a long, 6-foot cord.
Best for Small Tanks: Eheim Jager Aquarium Thermostat Heater
This old school aquarium heater from German company Eheim will keep the water in your smaller aquarium—up to 10 gallons in size—in a healthy range of 65 to 93 degrees. You can use the TruTemp dial to precisely recalibrate the heater by up to 8 degrees in either direction if you notice it running slightly high or low. It has a thermo safety control, which will automatically turn it off if/when your tank starts to run low on water. With double suction cups, the heater readily sticks to the side of your tank. It’s made of shock-resistant and shatterproof glass.
Best for Betta Fish: Marina Betta Submersible Aquarium Heater
This thin, flat 8-watt heater is designed specifically with betta fish in mind. It is safe to use in plastic or glass tanks up to 1.5 gallons in size and keeps the water warmed to 75 to 85 degrees. (Experts recommend betta fish live in 75 to 80 degree water).
This heater doesn’t have an on/off switch, but you’ll know it’s working thanks to its red indicator light. When it’s time to clean the tank or switch out the water, unplug it and let it cool for 15 minutes first. The exterior is made of a polymer that’s more durable than traditional glass, which you’ll appreciate during those cleanings.
Best Splurge: Innovative Marine Helio PTC 200 Watt Aquarium Heater w/ Controller
This heater costs more than others, but those who are serious about their in-home marine reef aquariums say the innovations are well worth the investment. For starters it has two 100-watt heaters to safely heat up to a 50 gallon tank. It does so using Positive Temperature Coefficient (PTC) technology, meaning it contains solid state ceramic chips. This allows the device warm up quickly, and heat evenly with no hot spots, and keep a low surface temperature. It's self-regulating to turn off when it reaches a predetermined set temperature.
Should there be any unexpected temperature fluctuations, the Smart Controller will instantly alert you. An additional benefit is that this heater uses less energy than some similar models.
Best Electronic: hygger Fast Heating Titanium Aquarium Heater
With a large, easy-to-read LED temperature display, you’ll always rest assured that your finned friends’ home is at the exact right temp. The submersible heater is made of premium titanium and double sealed by a black protective guard, which means should your fish touch it they won’t get burnt and the heater itself is resistant to explosion and corrosion.
It includes a run-dry protection that automatically turns the unit off if the water gets too low. An external temperature control means you won’t have to get your hands wet when you want to adjust the temp. The 500 watt unit is made for fresh or saltwater tanks 60 to 120 gallons in size.
Best for Reptiles: AIICIOO Under Tank Heater Reptile Heating Pad
If your aquarium is home to certain species of lizards, snakes, turtles, or frogs, you’ll want an under tank heater that runs without water. This top-rated heating pad contains a nichrome heating wire for fast, steady, even heating, and PVC material for insulation to keep the pad—and your tank—warmer for longer. This heater can be stuck to the side of your tank, which is recommended for hermit crabs among other animals. Note that you’ll need to purchase a thermostat separately to control the exact temperature of the pad.
For home aquariums up to 10 gallons in size, our top pick is the FREESEA Aquarium Heater Fish Tank Submersible Heater (view at Amazon). It’s well priced, reliable, and has a large LED temperature display. Those with smaller tanks, should consider the Eheim Jager Aquarium Thermostat Heater (view at Amazon). It allows you to calibrate the temperature function to suit your tank and will last for years to come.
What to Look for in an Aquarium Heater
Most fish aquarium heaters are submersible, meaning they should only be when under water. In fact, some will automatically turn off when the water levels get too low. Substrate heaters, which are used on the floor of the tank, are typically used with reptiles and/or plants.
Most aquarium heaters are rod shaped. Be sure to select one that isn’t longer than the depth of your tank’s water level.
Heaters run on wattage and the higher the wattage the greater the volume of water it can heat. As a general rule, you’ll want between 2.5 and 5 watts per gallon of actual water volume in the aquarium. Larger tanks may benefit from two smaller watt heaters as they’ll heat the tank more evenly.
Look for a heater with one or two suction cups that will securely attach to the inside of a glass or plastic tank.
Some heaters come with attached or built in thermometers. These are a nice reassurance that your fishs’ habitat is at the exact right temperature. If your heater doesn’t have one, you can purchase one separately.
Why Trust The Spruce?
This piece was written by Anne Fritz, who has been researching pet products for The Spruce for more than two years. Before writing this article, she gathered information from customer reviews, third-party articles, and brand websites' details. She also reviewed veterinary websites to learn about the healthiest habitats for different types of fish