Best Heaters for Betta Tanks (& Small Aquarium Fish): Safe, Reliable Options

When heating your small fish tank, it is important to select a heater that works effectively with smaller volumes of water.

After a long search for the best ones, I’ve come up with some great options, and the Aqueon Mini Aquarium Heater is the one that made it on top of my list!

Let’s take a closer look at the best heater for small aquariums with reviews of the following:

Product Details
1. Aqueon Mini Aquarium Heater

Premium Features

  • Fully Submersible
  • Shatterproof
  • Easy To Install
  • Great For Desktop
  • Up To 2 Gallons
Click here for best price
2. Marina Submersible Aquarium Heater

More Resilient

  • Easy To Install
  • Indicator Light
  • With Suction Cup
  • 8-Watts
  • Up To 1.5 Gallons
Click here for best price
3. Eheim Jager Aquarium Heater

Steady Heat Levels

  • Easy To Install
  • With Suction Cup
  • In Lab Glass Jacket
  • 18-34°C
Click here for best price
4. Cobalt Aquatics Neo-Therm Heater

2-Way Display

  • Thermal Protection
  • 1-Touch Setup
  • +/- Range Of 0.5°
  • Fully Submersible
Click here for best price
5. Fluval Submersible Aquarium Heater


  • Sleek & Compact
  • Dual Suction Cups
  • Borosilicate Glass
  • 68-86°F
Click here for best price

Best Small Aquarium Heater Reviews

1. Aqueon Mini Aquarium Heater

Aqueon’s Mini Aquarium Heater is a 5-watt energy-efficient heater that is not only beginner-friendly but also heavy-duty.

For a 5-watt heater, you’d be expecting low capacity, however, this heater maintains a steady temperature even in tanks that hold two gallons of water! It is made of shatterproof material and can be placed anywhere in the tank, you can even fully submerge it.


  • Suction cups make it easy to install
  • Constructed with safe and durable material
  • Designed for aquariums that contain half-gallon up to two gallons of water


  • Requires resetting after a certain timeframe


2. Marina Betta Submersible Aquarium Heater

Save energy and allow your betta to thrive with the 8-watt Marina Betta Submersible Aquarium HeaterThis heater was specifically designed to set and maintain a specific temperature for bowls and tanks up to 1.5 gallons.

Its resilient exterior is constructed of durable polymer, and its suction cups allow for easy installation. Its simple design allows it to fit along with the other elements in the tank, and just right above is its red indicator light to let you know when it’s on.


  • Made of durable polymer
  • Does not require manual adjustments
  • Has an indicator light
  • Can heat and maintain up to 1.5 gallons


  • Needs occasional monitoring


3. Eheim Jager Thermostat Aquarium Heater

The Eheim Jager Aquarium Heater is a small heater with a basic design and easy operation. It helps your aquarium maintain the perfect temperature. Equipped with its precise control, simple recalibration, and a control lamp that’s easy to read, this top-rated heater helps you create a comfortable home for your finned warrior family.


  • Adjustable temp from 18-34°C
  • Lab glass jacket to increase the heating surface
  • Constant temperature


  • Will struggle for a bigger tank


4. Cobalt Aquatics Neo-Therm Heater

A heater with a modern look and built to last, This 25 watts Cobalt Aquatics Heater is designed with a shatterproof outer casing that should provide you with a unit that is durable. The modern design is very thin, which is a great feature when used with a smaller tank.

The Neo-Therm is able to supply a temperature range from 66 to 96 degrees Fahrenheit. A one-touch control system allows you to make adjustments more easily than other heater designs. Thermal protection circuitry adds a nice safety feature that can shut down the heater before it overheats.

You may find this compact unit working overtime with tanks that approach or exceed ten gallons in water volume. The LED display offers the temperature setting as well as water temperature readings.


  • The Neo-Therm comes with a three-year warranty
  • A flat design that is one-third of an inch in thickness
  • Can maintain higher temperature ranges up to 96-degrees Fahrenheit


  • This heater comes at a higher price point than some units in the smaller range
  • Water temperature may be one or two degrees less with ten-gallon tanks or larger


5. Fluval Submersible Glass Aquarium Heater

The Fluval Submersible Glass Aquarium Heater provides sleek and compact heating in both freshwater and saltwater tanks. With its unique reflective technology, the heater automatically blends in and camouflages. It is made from high-density ceramic.

With a high-density ceramic outer core and a shock-resistant borosilicate glass-encased heating element, you can rest assured of its durability. The package includes dual suction cups that make its attaching and detaching easier!


  • Exceptionally durable
  • Temperature ranges from 68 to 86 degrees Fahrenheit
  • Easy installation


  • Requires water level maintaining


What Size Of Aquariums Does This Article Focus On?

When we are writing about small freshwater aquariums, what we will be focusing on are tanks that range between 3 to 10-gallons in size. The aquariums in this range are a popular choice for a beginner’s first fish tank. The 10-gallon sized tank is often sold in kit form, with everything a novice will need to get a tank up and running.

Tanks Less Than One Gallon

Freshwater fish aquariums that are one gallon and below are not really suitable for fish keeping. However, if your tank is this size and you would like some options you should look towards the eight-watt Marina Betta Submersible Heater.

Heaters For Tiny Fishbowls

Fishbowls are a controversial way to house your fish, and we do not recommend them (especially for betta fish – no matter the common myths you may have heard). They offer your pet a poor quality of life and may also cause health issues or even premature death. If you have no other choice than to use such a container to keep your fish, placing something like the Aqueon’s Mini Aquarium Heater underneath the gravel may be an option.

A Note About Water Temperature And Fluctuations In Smaller Tanks

Fish are unable to maintain their own body heat as they are poikilotherm animals. Because they are unable to generate body heat, it must be generated from the outside. This means that fish will use the tank environment to help them keep a proper temperature.

Due to this, a freshwater aquarium must be able to maintain temperature ranges between 71 and 86 degrees Fahrenheit on average (and even more specific temperature ranges for certain freshwater fish species).

A smaller aquarium will heat up and cool down much faster than a tank that is over 5-gallons.

The heater used must be powerful enough to keep the water at acceptable levels, but not too powerful, as this will cause fast changes in temperature and overheating the environment.

The temperature fluctuations experienced by a small tank require that any heater used is able to measure temperatures as accurately as possible. They must also be durable enough to withstand the constant cycling that they will go through.

Wide temperature fluctuations can cause stress for your fish, and water that is too extreme will cause health problems or even death for your pet.

Types Of Heaters And Their Compatibility With Small Freshwater Aquariums

A heater used for smaller tanks is designed similarly to those used with larger aquariums. A thermostat is set to the desired temperature range and a sensor will monitor the water conditions continually. When needed, a heating element will be activated to help maintain the temperature in the aquarium. There are several types of aquarium heaters, most of which will not work well with smaller tanks.

Immersible Heaters

These are also referred to as hanging heaters. They may be found in 10-gallon starter kits, but are considered less effective than submersible heaters. With aquariums smaller than 10-gallons, these systems are often too bulky for use.

In-Line Heaters

These types of heaters are located outside of the tank between it and the filtering system. This feature is a negative when space is a consideration (which is often the case for owners with a smaller tank). These heaters also come with a wattage power that is too high for small tanks and would exceed the temperature range quickly.

In-Sump Heaters

This type of heater is also located inside the filter/pump system itself. Size becomes an issue as most filtration systems for a tank under 10-gallons would be too small to house them. Higher wattages are also an issue with these units for the same reasons as with in-line heaters. Your best option to use will be a submersible heater.

Using A Submersible Heater For Small Aquariums

These heaters are completely submergible within the tank, which eliminates the need for an extra exterior room. A submersible design for smaller tanks must, therefore, be compact in design so they do not take up too much room.

Many fishkeepers feel that these units are more efficient at maintaining temperatures evenly within the tank. Another consideration when using these heaters in smaller tanks is wattage levels.

There are many submersible products available that offer the lower wattage range required for smaller aquariums. In aquariums that are between 5 and 10-gallons, you will want heaters with a level of 50-watts. In aquariums of 2 and 5 gallons, you should look towards a 25-watt heater.


After our reviews, we feel the Aqueon Mini Aquarium Heater is the best small aquarium heater. The durable design offers longevity and safety in your tank. The controls are easy to use, and the heat supplied is distributed evenly. This heater can fit a variety of tanks and tank set-up designs. It provides quality at a reasonable price point. Consider it when you next shop for a heater to use in your small freshwater tank!

Last Updated: October 17, 2021

Subscribe today and receive a FREE Betta Fish Care for Beginners eBook

Betta fish crazy? Yeah? Join our 10,000 subscribers and get betta fish fun, updates and our betta fish care eBook sent direct to your inbox for free.

Thank you for subscribing.
Check your inbox for instructions

Oops... Something went wrong.