It’s not a secret that fish and other aquarium habitats are cold-blooded creatures. It means that they can’t regulate their body temperature by themselves. Instead, they fully depend on their environment. This is why sustaining a comfortable temperature of aquarium water is crucial for their health and life. A device that is used to keep the water temperature at a due level is known as an aquarium heater.

Aquarium heaters come in a variety of types and sizes. By aquarium heater size, we mean its capacity, which is measured in watts. Knowing how to calculate the heating power depending on the tank size will help you choose the best aquarium heaters for various types of aquariums.

Table of Contents:

Aquarium Heater Types
How to Choose the Aquarium Heater Size Correctly
How to Use Aquarium Heaters: Useful Tips
Frequently Asked Questions

Aquarium Heater Types

Based on construction, three main types of aquarium heaters are distinguished. Each of them has its advantages and disadvantages. Choose the right option, taking into account the size of your aquarium and its type.

  • Hang-on heaters are the smallest and the cheapest but they tend to be less powerful and less effective than other options. As the name implies, they are mounted (hung) on the tank’s wall so that they are partly submerged in water.
  • Submersible heaters are mounted under the water on the tank’s back. They are effective and versatile: you can use them in both saltwater and freshwater aquariums.
  • Heating cables are placed on the tan’s bottom under the gravel. They are quite effective but specialists do not recommend using them in saltwater tanks.

How to Choose the Aquarium Heater Size Correctly

Essentially, larger aquariums require larger (and more powerful) heaters. Approximately, you need 2.5 through 5 watts to heat up one gallon of water. However, the amount of water is not the only thing to consider. There are two more variables: the temperature in the room and the desired water temperature.

To find an optimal heater size for your aquarium do some simple preliminary calculations. First of all, find how many degrees you need to raise the temperature on. For example, you need a temperature of 75 degrees while an average temperature in the room is 65 degrees. It means you need to add 10 degrees. The volume of your aquarium is 30 gallons. The right heater capacity will be 75-100 watts.

Use the chart below to find the best heater size for your aquarium. If you received a borderline value (e.g. 75-100), opt for the larger size (100).

Aquarium size (gal.)Add 9 degrees FAdd 18 degrees FAdd 27 degrees F
525 W50 W75 W
1050 W75 W75 W
2050 W75 W150W
2575 W100 W200 W
40100 W150 W300 W
50150 W200 W2 x 200 W
65200 W250 W2 x 250 W
75250 W300 W2 x 300 W

How to Use Aquarium Heaters: Useful Tips

  1. If you use two heaters simultaneously, don’t place them close to each other. Instead, try to place them at the opposite corners of the tank to make water heat up evenly.
  2. Two 75-watt hang-on or submersible heaters are better than one 150-watt heater. They provide an evener heating while the load on each device is smaller. Also, it’s a good idea to have one spare heater just in case of the main heater outage.
  3. The length of a vertically placed heater must correspond with the aquarium height. Heat tends to rise up, and if the tube is too short, the lower layers of water may stay cold.
  4. Consider potential temperature fluctuations in the room. Try not to place an aquarium near heat sources, open windows or under a vent.
  5. Switch off the heater before changing water. You should never leave a plugged-in heater outside the water or it can overheat and break down.

Frequently Asked Questions

To sum the things up, here are short answers to some popular buyers’ questions. Check yourself if you are still not sure how to choose the right aquarium heater size. We hope our tips and recommendations will help you to find the best option.

Q: What Size Heater Do I Need for My Fish Tank?

A: It depends on the tank size, the temperature in your room, and the target temperature of water in the aquarium. Use the chart above to make the right choice.

Q: What Size Heater Do I Need for a 65-Gallon Aquarium?

A: A 200-watt heater is sufficient if you need to raise the temperature on 9 degrees F. For raising the temperature on 18 or 27 degrees, you need 250 or 500 watts respectively.

Q: What is the Most Reliable Aquarium Heater?

A: Submersible heaters are considered reliable and effective. Try to choose products from reputable brands, such as Fluval, Tetra, or EHEIM.

Q: What Temperature Should My Aquarium Be?

A: It depends on what fish species you have. Coldwater fish feel good at the temperature of 65-68 F while tropical fish need the temperature of 75-80 F to feel comfortable.


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