How to Choose the Right Fish Tank Heater? Complete Aquarium Heater Guide

Aquariums are closed ecosystems in which we try to mimic the natural habitats of fish. We use heaters to provide the temperatures that the fish are accustomed to in their natural environment in our aquariums and to ensure that the water temperature is constant.

Aquarium heaters are indispensable equipment, especially for tropical fish aquariums. Especially in winter, it is absolutely necessary that the aquarium water is at the required temperature and that the water temperature must be maintained. Constant changes in water temperature weaken the immune system of the fish. You must ensure that the temperature of the water remains constant and at the temperature required by your fisherman. There are many types and strengths in the market. If you are confused about these options, find out how to choose the right aquarium heater in our article.

What Types of Aquarium Heaters are on the Market?

There are many brands and models of heaters used in the aquarium. The size of the aquarium is important in order to choose the right one for you. In other words, you should not buy a 150-watt for a small aquarium, nor should you buy a 100-watt for a big aquarium. For this reason, before you buy a heater, try to find out how many liters of aquarium your product is suitable for. Choosing the best and the best type of aquarium heater suitable for your aquarium is also important as you think. Other than that, the remaining features are only details that provide ease of use and comfort, so you can choose according to your taste.

Aquarium heater types:

  • Glass Aquarium Heater
  • Steel Aquarium Heater
  • External heater between the hose
  • Aquarium Bottom heater
  • Cable Aquarium heater

In addition, heater types are diversified among themselves, with or without a thermostat. Apart from this, there is a classification such as 25 watts, 50 watts, 100 watts, 150 watts, 200 or 300 watts that express the power of the product you bought. The most important factor in choosing a heater is power.

What to Consider When Choosing an Aquarium Heater?
When you buy an aquarium heater, the most important issue you should pay attention to is the operating range of heat. The equipment you will purchase must have a range that can provide the water temperature in which the fish can be healthy in order to provide the natural living environment and also must be able to maintain this temperature stably.

It is important that the equipment you choose has a thermostat in order to keep the heat constantly. Although the prices of an aquarium heater with a thermostat are slightly higher than those without a thermostat, it is necessary to keep your fish safe. If you are going to use a equipment without a thermostat, you should definitely get an aquarium thermostat and check the water temperature frequently. Because of the variability of the aquarium water weakens the immune system of the fish, and cause stress in fish. Constantly changing or lower water temperature than it should have can cause the fish to become ill and cause stress.

An important issue that you should pay attention to when choosing a heater should be its power and size. You should choose a equipment suitable for the height of the fish tank. It will be much easier if you choose a equipment that shows the minimum water level on it. In this way, you can immediately notice when the water level in the aquarium is low.

If the heater you choose is a bottom heater, you can use it completely in water. These types of equipment are particularly suitable for horizontal use at the bottom of the aquarium and for use at low water levels. The aquarium bottom heater, which is used horizontally completely in water, is also ideal for a terrarium.

The power of the fish tank heater you choose should also be suitable for your fish tank. As we mentioned before, for a large fish tank, it is not enough to put a 25-watt or 50-watt equipment and it will not heat the water. For this reason, you must first calculate the volume of the aquarium and choose a equipment that is powerful enough to heat this volume of water. In addition, for a little more comfort, you should pay attention to the warning light of it. The light turns on when the equipment is turned on and goes out when the water heats up and the thermostat turns off. In this way, it is easy to follow the temperature changes in the aquarium.

High-quality fish tank heaters can measure precisely and immediately detect very small changes in water. This ensures that the fish in the aquarium are healthier. It is important that the equipment you choose has a safety control mechanism. In this way, when the fish tank heaters go out of the water or when the water level drops, this mechanism cuts the electricity and provides safety. Otherwise, your fish tank heater will break down.

Aquarium Heater Size Guide in Gallons

Β Tank SizeΒ Difference Between Target and Room Temperature
Β 10 Β° FΒ 20 Β° FΒ 25 Β°F
5 Gallon25 watt50 watt75 watt
10 Gallon50 watt75 watt75 watt
20 Gallon50 watt75 watt150 watt
25 Gallon75 watt100 watt200 watt
40 Gallon100 watt150 watt300 watt
50 Gallon150 watt200 watt2 x 200 watt
65 Gallon200 watt250 watt2 x 250 watt
75 Gallon250 watt300 watt2 x 300 watt

Aquarium Heater Size Guide in Liters

Β Tank SizeΒ Difference Between Target and Room Temperature
Β 5 Β° CΒ 10Β Β° C15 Β° C
20 Liter25 watt50 watt75 watt
40 Liter50 watt75 watt75 watt
75 Liter50 watt75 watt150 watt
100 Liter75 watt100 watt200 watt
150 Liter100 watt150 watt300 watt
200 Liter150 watt200 watt2 x 200 watt
250 Liter200 watt250 watt2 x 250 watt
300 Liter250 watt300 watt2 x 300 watt

Where Should I Put the Aquarium Heater?

It is generally suitable for use in the corner of the tank. It is helpful to place the equipment near fish tank supplies such as an aquarium filter. In this way, the warmed water is distributed more quickly within the aquarium. The middle parts should not be either in the passage of the fish.
If a bottom heater is used, the entire equipment can be inserted into the aquarium. Some heaters are only suitable for vertical use. Therefore, it is recommended to read the user manual of your fish tank heater before use.

What Should Be Considered When Using Heater?

  • If you are using a thermostat heater, the heater must be kept on constantly. When the water reaches the desired temperature, the heater will stop working. When the water temperature drops, the equipment will start working. These types of heaters are more efficient because they work according to the water temperature.
  • When using an fish tank water heater, the most important issue you should pay attention to is not to operate the equipment outside the aquarium, in a dry environment.
  • If the water level has decreased without you noticing and the heater is working, the first thing you should do is to unplug it and take it out of the aquarium after waiting for at least half an hour to cool down.
  • When the water level is low, you should not add water without cooling the fish tank heater and taking it out of the aquarium. If you pour water on a equipment that has worked without water, the heater glass may break.
  • Fish tank heaters are water-resistant. There are also varieties that can be completely submerged in water.
  • Nevertheless, it is safer for only the resistance part of the heater to remain in the water and the top part where the temperature adjustment knob is out of water.
  • You should definitely not put your hand into the aquarium while the heater is running.
  • You should not take it out of the water while the equipment is running. When you take it out of the aquarium, you must unplug it and take it out after it has cooled for 15 – 20 minutes.
  • The equipment must be fixed in the aquarium with the help of suction cups and its movement must be prevented.
  • If possible, you should use two small equipment instead of one very powerful equipment. In this way, you can be sure that the water in the tank is heated homogeneously.
  • If you position the heater close to equipment with strong water circulation (filter, etc.), you can ensure that the warm water is distributed in the aquarium.

Is a Backup Heater Essential?

Heaters are susceptible to failure due to their mechanical structure. Water temperature is vital for fish. Therefore, it is critical that the water temperature is at the desired temperature and constant. Many aquarists have encountered fish deaths due to failed equipment. Therefore, it is important to use a backup heater.

How Should I Use Backup Heater?

You should set your backup equipment at a temperature a few degrees lower than your main heater. It is helpful to observe the equipments during the first installation as the thermostats of the heaters can sometimes be out of order. While your main heater is running, your backup equipment’s heating lamp will be off. If the lamp of your backup heater is on, you can understand that your main heater has failed. Since the backup equipment will not operate under normal conditions, the backup equipment will last longer than the main equipment.


Aquarium heaters are critical in the aquarium and quality products should be used absolutely. Please do not use poor quality equipment for both you and your fish healthy.

πŸ π™ƒπ™‹ Team
πŸ π™ƒπ™‹ Team
We're just like you - aquarium enthusiasts who love aquatic life! We've been caring for and breeding all sorts of freshwater and marine aquarium fishes, plants, and other pretty little creatures for years. We love sharing our knowledge with other fish hobbyists, and this article you have just finished reading is the best proof of that. You can read more about us here.

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