Best Aquarium Heaters [2021 Complete Guide]

Best Aquarium Heaters [2021 Complete Guide]

Supplying your fish tank with the right heater is imperative for the well-being of your fish. When shopping for the best aquarium heaters, you need to consider several factors, such as temperature settings, compatibility, safety features, and more.

Considering the variety of aquarium heaters on the market, let us guide you through some of our top picks. This article will also cover what you should keep an eye on when purchasing a fish tank heater and what to avoid.

Best Aquarium Heaters Reviews

Rarely does anyone’s home maintain the same temperature throughout the entire year. Because room temperature affects the fish tank temperature, your fish can also be influenced by these changes. Cold water can cause your fish to feel stressed, ill, and in some cases, it can shorten their lifespan.

To prevent this from happening, many aquarium owners prefer installing an aquarium heater. By maintaining and shifting the tank’s water temperature according to your fish’s needs, you will guarantee a healthy environment for them. Below you’ll find our best aquarium heaters reviews.

Aqueon Pro Adjustable Heater, 150W

This high-quality aquarium heater is a favorite among fish tank owners, and here’s why. The Aqueon Pro Adjustable Heater comes in 50-, 100-, 150-, 200-, and 250-watt output levels, although we highly recommend the 150W model.

One of its most essential features is the ability to set the temperature, which can be adjusted from 68° to 88° F. It also comes with LED lights that will let you know if the water has reached its highest set limit.

When the indicator light turns red, it means that it’s still emitting heat. When the water is warmed to the desired temperature, the lights will turn green, and the heater will automatically turn off.

This fully submersible heater can be placed either vertically or horizontally in your tank. Furthermore, it can be used for both freshwater and saltwater fish. Since it comes in different sizes, it can be installed in practically any type of tank.

This tank heater is made of thermoplastic, which means that it’s basically unbreakable. What’s more, its rugged plastic cover prevents the heat from harming the fish.


  • Adjustable in terms of aquarium size
  • Indicator light
  • Lifetime assurance
  • Durable plastic construction
  • Affordable


It might be difficult to read the temperature dial

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Finnex Hang-On Electronic Controller Aquarium Heater

What sets this aquarium heater apart from the rest is its titanium tube. Not only is it virtually indestructible, but the titanium heater warms the water much faster than other materials.

Through the electronic controller, which hangs outside of the tank, you can adjust the temperature within the range of 2°.

Another one of its capabilities is that it’s resistant to corrosion, which also makes it long-lasting. It can be installed in both freshwater and saltwater tanks without difficulty.

In terms of wattage, it can range from 100W to 500W. We recommend opting for the 300W heater, which can be used for tanks with 80 to 100 gallons of water.

The Finnex electronic heater also comes with a LED indicator light, switched on whenever the heater is warming up the tank water.


  • Titanium heater
  • Corrosion-resistant
  • Compact size
  • Clip-on electronic controller


Unreliable temperature accuracy

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EHEIM Jager Aquarium Thermostat Heater

This fully submersible heater is very long, so it’s better suited for deeper tanks. If you can manage to place it vertically in your aquarium, the thermostat dial will be near the tank’s surface, and you’ll be able to set the temperature more easily.

The thermostat allows you to set the temperature from 65° to 93° F. When you first set up your thermostat heater, you will also need to go through a calibration process a few days in a row after its initial setup.

Once removed from the water, it automatically shuts off, and the moment it’s placed back in, it will start again, consistent with the most recent temperature settings. Another fantastic feature is its ability to process changes in water levels, after which it will automatically turn off.

It’s suitable for both freshwater and saltwater fish tanks. This aquarium heater is made from shatter-resistant glass, which is unaffected by chemical and biological substances.


  • Shatterproof glass construction
  • Fully submersible
  • Accurate temperature dial
  • Low cost
  • Thermo safety control


The calibration process can take too long

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Cobalt Aquatics Flat Neo-Therm Heater

Another favorite among fish tank owners, the Cobalt heater comes with an excellent reputation. One of its top features is its capability to display the desired water temperature and the actual tank temperature at the same time. What also sets it apart from other aquarium heaters is its easy one-touch system.

Made of solid thermoplastic, which makes it shatterproof, aquarium owners need not worry about overheating. You can find it in 25, 50, 75, 150, 200, and 300 watts, and it can adjust the water temperature from 66° and 96° F.

In comparison with other aquarium heaters we’ve listed so far, the Cobalt is more compact, fully submersible, and doesn’t ruin your tank’s aesthetic.

The heater, which comes with a three-year warranty, can be installed in freshwater and saltwater tanks, as well as terrariums. Its protective covering is safe for any aquatic animal.


  • Easy to operate
  • Aesthetic design
  • Convenient size
  • Great protective coverage
  • Safe and reliable


  • Expensive
  • Suction pads tend to get loose quickly

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ISTA 150w/300w/500w In-Line External Heater Aquarium Heater

As opposed to our other picks, the ISTA in-line heater is external, meaning that it is attached to the tank wall’s outer side. Therefore, it has to be positioned vertically, and it must be connected to the filtration system. If you want to save some space in your aquarium, this is an excellent option.

It comes in six different models, and its sensors accurately detect water temperature. Once the water is warmed up, the heater will automatically switch off. You can set the temperature manually by simply pressing the button on the screen.

It’s suitable for both fresh and saltwater tanks. Thanks to its heat-resistant protective covering and its superb quality, it’s resistant to corrosion.


  • It provides more space
  • Easy to install
  • Heat protection glass
  • Auto-power safety system


It only shows the water temperature in Celsius

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Buyer’s Guide

When you are in the market for an aquarium heater, there are some factors you need to consider before purchasing one. Here are some key aspects of fish tank heaters that you need to look for.

Types of Aquarium Heaters

Before we go into the details, let’s take a look at different types of aquarium heaters and which one would work for your fish tank.

Hanging and Submersible Heaters

These are the most popular types of heaters. The only difference between them is their ability to function while being underwater.

A hanging heater shouldn’t be placed directly in the water but rather be attached to the aquarium’s top. On the other hand, submersible heaters are intended for underwater usage, and they are installed by placing the suction cups on the aquarium’s inner wall. These types of heaters are long-lasting and very reliable.

In-Line and In-Filter Heaters

As opposed to submersible heaters, in-line heaters are found on the outer side of the tank wall.

The main difference between in-line and in-filter heaters is that in-line heaters are linked to a canister filter line that goes into your tank, while in-filter heaters are located inside the canister filter.

These two types of aquarium heaters are a good option if you have curious fish, which might get hurt by submersible heaters. They are also much easier to clean.

Substrate Heater

This type of tank heater consists of a cord with a built-in thermostat, and it’s located at the bottom of your aquarium. Substrate heaters are also the best option for plants in terrariums since they boost their growth.

Because they don’t measure your water temperature the same way submersible and in-line heaters do, they may not be the best option for your fish.

Sump Heater

Similar to hanging heaters, sump heaters are installed inside of your sump. It’s not as popular as other types of heaters, but it gets the job done as well.

Level of Safety

When purchasing an aquarium heater, be mindful of the type and model of the heater. Do some research about your fish and find out what their typical behavior is around heaters. They can easily be distracted by them, and they could get hurt if they get too close.

Search for heaters that turn off automatically once they reach the desired water temperature. Overheating your tank could cause big problems. Conversely, if the water temperature drops, the heater will start on its own.

Similarly, aquarium heaters also come with a LED indicator light which will notify you when the water temperature reaches its optimal level.

Wattage in Relation to Aquarium Size

Your heater’s wattage level indicates the amount of power it uses to heat the water. The general rule is that for every gallon of water, three to five watts are required. Following this rule, this is how many watts your aquarium heater would need:

  • 50 watts for 15 gallons of water
  • 100 watts for 30 gallons of water
  • 200 watts for 65 gallons of water
  • 300 watts for 100 gallons of water

If you have a huge aquarium, consider getting two tank heaters rather than purchasing one high-wattage heater.

Water Temperature Control

Even if you find an aquarium heater that does a marvelous job of heating the tank water, using it can still be complicated. But it doesn’t need to be. Here’s what the best water heaters usually offer:

  • The option to access the temperature settings
  • Digital thermostats and dials that allow you to adjust the water temperature
  • Temperatures that are displayed numerically


Aquarium heaters vary in price, based on the heater’s type, wattage, quality, material, options and features, size, and many more aspects.

Considering it’s an object you will be using for a long time, they tend to be somewhat pricy but worth the investment. Exterior models tend to be less expensive than submersible heaters.

What can also affect the price is the store where you purchase it and whether it’s ordered online. Also, note that not only will the actual purchase affect your wallet, but your electrical bill as well.


How Many Heaters Do I Need?

You would usually need one aquarium heater for your tank. And depending on the size of your tank, you’ll need to choose a tank heater with the appropriate wattage levels. You can find a guide with the proper wattage-to-tank-size ratio in the previous section.

If you have a significantly large aquarium, then consider buying two heaters. Instead of placing them beside the other, make sure they are installed on opposite sides of the tank. That way, heat will emit from both sides equally.

Where Should I Place My Heater?

This depends on the type. Submersible heaters are supposed to be placed inside the tank while hanging, and in-line heaters go outside the tank.

Placing your aquarium heater near a filter inlet/outlet or a circulation pump is advised to ensure the heat is distributed equally.

Also, make sure to find heaters that are the right size for your aquarium. The tube of your heater should match your tank’s height.

Final Verdict

We’ve presented you with some of the best aquarium heaters there are on the market. Considering the various features they have and their value and quality, we believe one beats all the rest – the Cobalt Aquatics Flat Neo-Therm Heater.

This aquarium heater is the best due to its accessible touch-screen thermostat, the variety of reliable models it offers, its flat aesthetic design and compact size, and its nearly indestructible covering.