Best Heater For Small Aquarium (Tanks Of 3-10 Gallons)

Choosing the best aquarium heater for small tanks is always a big thing to consider. 

The main challenge comes from the limited space inside with decoration and fishes. Not only that, with a heater, but the small size may also cause the aquarium to heat up quickly.  

So, assuming that you have a fish tank with the size, not more than 10 gallons. How should you do, and what are ideal heaters to pick?

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Top 5 Of Best Heaters For Small Fish Tanks

In this article, we pick 5 of many best heaters for small fish tanks on the market these days. Basing on the size, compatibility as well as efficiency, we consider them. We know for sure that all of these five will never let you go wrong. 

Product Images Product Name Editor's Rating Prices
Cobalt Aquatics Flat Neo-Therm Heater 3.8 out of 5 stars (3.8 / 5) See price on Amazon
FREESEA Aquarium Fish Tank Submersible Heater 4.2 out of 5 stars (4.2 / 5) See price on Amazon
Hydor Submersible Glass Aquarium Heater 3.5 out of 5 stars (3.5 / 5) See price on Amazon
Tetra HT Submersible Aquarium Heater 4 out of 5 stars (4 / 5) See price on Amazon
GOOBAT Mini Betta Heater 4.1 out of 5 stars (4.1 / 5) See price on Amazon

Now, it is time to explore one by one. 

Cobalt Aquatics Flat Neo-Therm Heater

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For the first idea of the list, we recommend you on the heater from the Cobalt Aquatics brand. It has a durable shatterproof encasing layer and runs by the wattage level of 25.   

Another feature makes the device suitable for a small aquarium is its modern compact flat design. Plus, the submersible and the reversible structure help you place it flexibly inside the tank.

Next, the heater comes with a one-touch control system. You can easily adjust the temperature between 66 and 96°F. 

Besides, we love to mention the thermal protection circuitry. This part reduces the risk of overheating. We mean that it will automatically shut off when the temperature reaches the desired level. 

It is not that we find no drawback with this Cobalt Aquatics heater. The minus point is the water temperature. In comparison with larger tanks, small tanks with this device have about 2°F cooler water.  


  • Compatibility with up-to-6-gallon aquariums
  • Compact submersible design
  • One-touch control system
  • Overheating protection
  • Warranty within three years


  • Lower-than-normal water temperature

FREESEA Aquarium Fish Tank Submersible Heater

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Next, we turn to an oval-shaped heater of the FREESEA brand. While the first recommendation is for tanks from 1 to six gallons, this one is suitable for up-to10-gallon aquatic spaces.

There is a shield covering the whole device. So, when the heater sits entirely under the aquarium, no water can damage its operation. On the front of the device, it is a bright LED display for you to view the temperature clearly.

In addition, the FREESEA heater runs with the power-off memory function. In case of power failure, the device will save the preset temperature and resume when the power is on. 

Also, the automatic constant temperature function is available. To prevent the risk of overheating, the heater shuts off when the temperature reaches the preset level. 

To be honest, it will be a perfect choice if the warranty term is longer than one year. 


  • Compatibility with 1-to-10-gallon aquariums
  • Automatic constant temperature function
  • Submersible design
  • A bright LED displaying temperature
  • Power-off memory function


  • Short-term warranty

Hydor Submersible Glass Aquarium Heater

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We have already mentioned above that tough plastic heaters are always durable than glass ones. However, this Hydor heater is a different story.

The Hydor glass heater comes with the PTC technology with high shock resistance. So, it tends to be more durable than many other glass heaters on the market. Despite the 100% submersible design, there will be no damage in case of suddenly getting dry.

You can see that a cord is available with the heater. Its length is around 70 inches. Assuming that the tank is not near the wall power socket, it does not matter then.

However, for years of use, the temperature reading seems to be less accurate. The number tends to change at different positions around the tank.


  • Shock and shatter resistance
  • Durability
  • Submersible design


  • Inaccuracy temperature reading

Tetra HT Submersible Aquarium Heater

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If you are tired of adjusting the heater with a complex control system, we recommend this Tetra HT one. 

It is a type of non-adjustable submersible heater for the aquariums with the size ranging from 2 to 10 gallons. Furthermore, the heater is quite perfect to hide behind the aquarium decoration because of the compact design without LED display. 

There are only two indicator lights including red and green. For the red light, the device is on the process of heating the tank. And when it turns green, the temperature is at 78°F – fixed level of this heater.

The simple control is an advantage and disadvantage as well. You cannot choose any other temperatures except for 78°F. This level will be suitable for tropical fishes at best.


  • Long-term warranty of two years
  • Automatic thermostat
  • Submersible design
  • Compatibility with 2-to-10-gallon aquariums


  • Fixed temperature

GOOBAT Mini Betta Heater

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Another heater with no need for manual adjustment is the GOOBAT Mini Betta heater. We love this device so much because of it extremely compact submersible design. It seems to be the smallest option that we collect for the list.

Made of PPC plastic, the heater comes with high durability than any traditional glass ones. Plus, the suction cup included will help you install the device easily. 

It runs with the wattage of 15 and shows the compatibility with 1-to-1.5-gallon tanks. If the indicator light is red, it means that the heater starts heating the tank. When you see the green light, the heating gets done. 

Don’t forget to bear in mind that there is only a fixed temperature at 78°F. So, you had better choose suitable fishes for the aquarium with this heater. 


  • Compact submersible design
  • Durability 
  • Simple control system


  • Fixed temperature

Aquarium Sizes That We Focus On

When searching for the best water heater for a small aquarium, we focus on the sizes between 3 and 10 gallons. 

Are you wondering the reason why?

Firstly, for those who are beginners caring for fish tanks, this range is the most common choice. Moreover, these tanks often go with a kit that will be in need for tanking up in the future. 

Secondly, for the less-than-1-gallon tank, it is not an ideal option to keep fishes in. If you still want to try this size, we suggest you choose an 8-watt heater. 

No 3-10-gallon aquariums! No less-than-1-gallon one! Some people look for heaters used for small fish bowls. We do not think it is a good idea and such a controversial option instead. 

Inside the tank, it is an uncomfortable space for fishes to live. Consequently, they have to struggle with many health problems and even premature death. However, if there is no better choice than a fishbowl, you can use a 4-watt heater. 

Types Of Heater For Small Freshwater Aquarium

For fish tanks with a size between 1 and 10 gallons, we suggest two types of heaters. They are preset heaters and adjustable heaters.

Preset heater

We call it the always-on type. The device maintains a certain desired level of heat that you preset. However, because of the naturally fluctuating water temperature, we find the preset heater with a drawback. 

For example, in some places, the daytime temperature tends to be higher than the nighttime one or vice versa. It seems to be hard to forecast the weather that can affect the water temperature inside the tank. You preset the device, and the risk of overheating may come then. 

Adjustable heater

Unlike the preset heater, an adjustable heater can automatically regulate the temperature thanks to a thermostat. 

For instance, you set the temperature of 78°F. The device shuts off automatically after reaching this level. And it will turn on when water tends to cool down.

The adjustable heater helps to prevent the risk of overheating. But it is not a budget-friendly option with a little bit of bulky design. 

Submersible Heaters Are The Best Choices 

Due to the compact submersible design, this heater does not require any extra room outside the tank. Plus, it comes with a LED light on the top to let you know whether the device is on or not. 

In comparison with the immersible ones, the submersible heater can keep the tank temperature more stable all day long. 

There is a tube encasing the coiled things of the heater. Some brands make this part with the glass, while many others choose the tough plastic. For better use, we suggest you choose heaters with the latter-mentioned material to reduce the risk of cracking.

When choosing the submersible heaters, you need to consider the wattage level, too. It depends much on the size of the tank.

  • A 25-watt heater for a 2-5-gallon tank
  • A 50-watt heater for a 5-10-gallon tank


Preparing the best heater for small tanks is also an important task when caring for an aquarium. The better the heater can run, the more ideal the tank will be for fishes to live inside. 

Besides the information above, if you need more help, feel free to let us know. We will be back with a lot of exciting recommendations.

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