Best Aquarium Heaters (Review & Buying Guide) 2019

Creating and maintaining perfect conditions for your pet fish can be difficult. Some species prefer colder aquarium water, while others prefer warmer temperatures, and some are just finicky and require the absolute best in order to thrive. No matter what your fish like, it’s vital to frequently monitor the temperature of their habitat and maintain the optimum conditions. To do that, you’ll need an aquarium heater.

With a good aquarium heater, you’ll easily monitor the water temperature and adjust it if needed, thereby keeping your fish safe and healthy. To help you find the best aquarium heater, we tested and reviewed dozens of different units, coming up with the following, best-of-the-best fish tank heaters list.

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Tetra HT Submersible Aquarium Heater

Tetra HT Submersible Aquarium Heater

Hydor In-Line External Heater

Hydor In-Line External Heater

ViaAqua 300W Quartz Glass Submersible Heater

ViaAqua 300W Quartz Glass Submersible Heater

Best Aquarium Heaters Buying Guide & FAQ

Having aquarium fish is a lot of work – you need special equipment, food, decorations, and of course, an actual effort to keep your fish healthy and happy. It’s easy to feed your pets from time to time, and perhaps even clean their aquarium when needed, but keeping their water at optimum temperature? Not that easy.

Since you can’t manually heat or cool the aquarium water to find ideal conditions for your fish, it’s crucial to find the right fish tank heater that can do that for you. Most heaters work automatically, meaning they ‘sense’ when aquarium water is below or above the set temperature, so they turn on to either warm or cool the water. Some heaters only have basic functions and can’t sense when the aquarium water is out of the set range, so you have to manually set the temperature you want the water to be. And then there are internal (submersible) and external (hang-on) fish tank heaters. Which one is the best?

To help you find the right fish tank heater for your fish, we’ve put together this handy buying guide and answered some of the frequently asked questions. Read on to make a fully informed purchase.

aquarium heaters

Aquarium Heaters And The Importance of Maintenance

Aquarium heaters are a critical piece of equipment that is absolutely necessary if you’re serious about the well-being of your fish. Heaters become even more important if you have a saltwater aquarium, but they may be necessary even if you don’t.

However, buying a fish tank heater is just a part of the equation – to keep the aquarium water at optimum temperature, regular maintenance is needed. By spending a few minutes on the heater maintenance every other day or so, you can save yourself from time-consuming and pricey problems, and your fish from life-threatening conditions. So let’s talk about the maintenance and how to prevent heater disasters.

  • Buy a high-quality aquarium heater

Yes, this is not a part of the heater maintenance per se, but to prevent serious disasters, it’s wise to first and foremost invest in a high-quality unit. This doesn’t mean that a top quality fish tank heater needs to be super expensive, but it does mean it should be made of a durable material, have accurate sensors and preferably come with some form of warranty.

  • Always follow the instructions

It’s not uncommon for people to install and use things without looking at the manual and instructions that come with the product. Don’t make that mistake – read and follow the instructions for installing, guidelines for cleaning, etc.

  • Use an aquarium thermometer

It’s always better if a fish tank heater has a thermometer included, however, even if it doesn’t, you can always buy a basic thermostat to help you monitor aquarium water and adjust the temperature for optimum conditions. Although a simple piece of equipment, the aquarium thermometer can greatly help in keeping your fish healthy and happy.

  • Consider using a temperature controller

If you’re often away from home and cannot check water temperature regularly, or your aquarium heater cannot automatically monitor and control fish tank water temperature, consider purchasing and using a temperature controller. This device automatically monitors and adjusts water temperature so that it’s always within the optimum range. This helps your fish live comfortably and may help your aquarium heater function better.

Things to Consider When Buying Aquarium Heaters

Before purchasing an aquarium heater, it’s important to consider a few things. First of all, what kind of fish do you have? You don’t want to buy a heater only to find out (in a very bad way) your fish prefer room-temperature water. Secondly, how big is your fish tank? If it’s very large, you don’t want to buy one small heater that won’t be able to properly heat aquarium water. There are many factors you should be aware of before buying a fish tank heater, so let’s get into the specifics.

  • Fish Type

As mentioned, before using an aquarium heater, make sure your fish actually need warm water in order to thrive. For example, fish like tetras, bettas, angelfish and guppies love their water nice and warm at all times, meaning it’s wise to keep the temperature very stable. Obviously, for that, you’ll need a top-quality heater.  Other fish like swordtails and barbs don’t mind slight temperature fluctuations, so although you always want to use a good-quality heater, you can relax a little with these types of fish.

  • Heater type

It’s good to know there are several types of aquarium heaters: submersible, external, inline and substrate. We’ll deal with each one in a bit more detail down below, but for now, let’s just say that some heaters are probably more suitable for your aquarium than others.

  • Heater size

Aquariums come in different shapes and size, and so do the heaters. To find the best fish tank heater for your aquarium, it’s crucial to get the right size. The bigger your fish tank, the greater-in-power (watts) heater you need. Generally speaking, 25-watt heaters are good for 5-gallon tanks, 50-watt heaters for 10-gallon tanks, 75-watt heaters for 25-gallon tanks, and so on.

  • Heater placement

Placement of the fish tank heater is another important thing to consider. If you have a large aquarium and don’t mind the look of the bulky heaters, you can easily find good-quality high-powered submersible heaters. They can be placed on the end or in the middle of the tank – the choice is yours. If, however, you prefer minimalistic look when it comes to heaters, it may be best to purchase a substrate aquarium heater, as they’re placed below the tank’s gravel and are less visible.

  • Additional features

And finally, keep in mind all the additional features that may come with a heater. For instance, it’s always a plus if a heater has or comes with a thermostat, as well as adjustable heat settings.  These features make monitoring and adjusting the water temperature much easier. Auto-shut off function also comes in handy in case the water overheats. Generally, although additional features are not an absolute must, they do tend to make everything easier – however, they also make the units more expensive.

Different Types of Aquarium Heaters

There are four types of aquarium heaters, and we’ll discuss main differences between them in this chapter. Read on to find out which heater is best suited for your aquarium.

  • Submersible heaters

These are the most common types of fish tank heaters. Usually, they need to be fully submerged in water in order to properly work, but can be installed horizontally or vertically, depending on your preferences and size of your fish tank. These units can be used for both freshwater and saltwater aquariums, and are suitable for small, medium and large tanks.

  • External heaters

Hang-on, or external heaters are basic and effective devices that are installed outside the aquarium, usually in a vertical position. They are usually less expensive than submersibles, but the drawback is that they are not always able to distribute heat evenly across the fish tank, so they’re best suited for smaller to medium-sized fish tanks.

  • Inline heaters

These types of heaters are attached to the tank filter, meaning they heat the water as it is pumped in, returning it warmer in the aquarium. They are very safe, efficient and pretty simple to use, although you usually need to purchase several different parts in order to install them.

  • Substrate heaters

As the name suggests, substrate heaters work by heating up the substrate of the aquarium via a cable that has a heating element inside. This cable is flexible and buried underneath the tank’s sand, which makes this particular heater very aesthetically pleasing, as you can’t even see it.  However, the substrate heaters are the least common types of water heaters, as many people find submersible, hang-on and inline heaters more practical.

heaters for aquarium

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Ideal Temperature of an Aquarium

The ideal temperature of a fish tank depends on the type of fish you have. Generally speaking, a good range is between 76° to 80°F, or 25° to 27°C, but some species require warmer water, while others demand several degrees cooler water. However, what’s true for all fish species is that they thrive best when water is kept at a constant temperature, meaning you need an aquarium heater of good-quality that will monitor the temperature and either adjust it when above/blow set range, or let you know when and how to adjust it.

  • Cold water fish

Cold water fish prefer cold or room-temperature (unheated) water, so it’s possible you may not need a heater if you own some of the following fish:

    • Goldfish
    • White Cloud
    • Bloodfin Tetras
    • Barbs
    • Zebra Danio, and others
  • Tropical fish

Tropical fish require warm or heated water, which generally falls within the range of 75-80°F, or 24-27°C. Therefore, if you own tropical fish, you definitely need a reliable fish tank heater that will keep aquarium water at optimum temperature. Some of the tropical fish include:

  • Bettas
  • Danios
  • Guppies
  • Swordtails
  • Platties, and others.

Because different types of fish have different needs, tropical fish should never be kept in the same tank with cold water fish.


Q:  How do aquarium heaters work?

A:  Fish tank heaters are pretty simple devices that help fish owners keep the temperature of their aquarium water within an optimum range. How do they do this, you ask?

Most heaters have a heating element inside them, encased in glass, ceramic, polymer or other durable material that makes submerging the heater in water safe. Some come with thermostats, others don’t, but those that do usually have adjustable heating settings. To monitor temperature changes, some heaters use bimetallic strip thermometers which are composed of two metals (usually steel or copper) that expand at different rates as the temperature changes. Other, more modern heaters, use intelligent microchip tech that is able to produce more accurate readings.

Q:  Why do aquarium heaters have to be submerged?

A:  Actually, not all heaters have to be submerged –for instance, external heaters are not to be placed in water but attached to the filtration system, while substrate heaters need to be buried underneath the tank’s gravel or sand.

However, submersible aquarium heaters usually need to be fully submerged in water in order to properly work. The general advice is to get a heater as long s the aquarium itself, so that the unit can allow even heating across the entire tank. So, naturally, to heat the water, the submersible heater needs to be inside it. But, even this depends on the model in question as some heaters can be partially submerged.

Q:  Can you have the cord of the submersible heater in the water and is it safe?

This is a common question among aquarium owners, and the answer is: yes, you can put the cord in water, and yes, it’s perfectly safe.

Pretty much all modern submersible heaters are designed to be fully submerged in water, cord and all. In fact, if your heater is fully submersible, it’s advisable to completely submerge it, as they have a “minimum water level” line anyway.

Q:  What Size Heater do I need?

A:  The size of the heater you need depends on two factors:

  • Your aquarium size
  • The ideal temperature for your fish

Some heaters are marketed for specific aquarium sizes, so it’s easy to find heaters for 10 gallons, 25 gallons, 50 gallons, and so on. While these units can be used as some form of a guide, it’s important to keep in mind that when it comes to fish tanks, sizes are not absolute. If, for instance, you own goldfish in a 10-gallon aquarium, you may not need an actual 10-gallon heater because goldfish are coldwater fish that don’t require heated water, except maybe slightly warmer (a degree or two) than room temperature. For this reason, most tank heaters are sold according to their power, or wattage.

Generally speaking, you want to take into account the ideal temperature for your fish species, current room temperature and the size of the aquarium. For example, if your fish require water of 75°F, and the room temperature is 65°F, you only need to raise the temperature by 10°F. This is easily done if you have a small to moderate-sized tank, as you only need a 25-watt heater, but if you have a larger aquarium, you may need a more powerful heater. For instance, for a 50-gallon tank, you’ll need a 150-watt heater to increase the temperature by around 10°F.

Q:  Do heaters wear out?

A:  Like all devices, aquarium heaters tend to wear out over time. Luckily, some come with a years-long warranty, but even those need proper care and maintenance from time to time. Here are some basic tips to keep your tank heater working properly for as long as possible.

  • Acclimate the heater: before you turn on the unit for the first time, let it acclimate to the current temperature of the aquarium. Set it up and let it sit in the water for about 60 minutes before you turn in on. Do the same thing when removing the unit from the tank (when cleaning, etc.), so that it can cool down properly. This should prevent potential shocks and help the device acclimatize.
  • Place it properly: always follow the instructions that come with the unit. Some heaters should be placed horizontally, some vertically, others should be fully submerged. Placing the device properly will keep your fish, the aquarium, and the heater safe and sound.
  • Clean it: like aquariums, tank heaters should be cleaned from time to time. Because this is a tiresome work, make sure you pick the heater that is easy to take care of. Still, no matter which unit you choose, regular cleaning is a must.

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Q:  Where should I place my heater?

A:  The best place to put your heater depends on the type of the heater you have. Of course, you can put your unit on the end, front or in the middle of the aquarium – the choice is yours, but you should also take into account the model and size of the heater.

However, placing the heater near the outflow, inflow or a powerhead is probably the best idea because this allows the unit to heat the water more evenly. Basically, when the aquarium water is flowing directly past the heater, heat is more evenly spread out throughout the tank.

And if you have a large aquarium? Consider purchasing two tank heaters which will be placed at the opposing ends of the aquarium. This allows heaters to properly and evenly heat a large amount of water, plus, in the event one unit fails, the aquarium will have another heating source.

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Q:  How safe are aquarium heaters?

A:  Most fish tank heaters are, simply put, safe. They’re designed to be safe around, in and on water, as well as for fish and humans. However, the longer you have the heater, the more there are potentials for accidents – if the heater is not properly managed and maintained.

For instance, cracked heaters present potential electrical hazards, and so do frayed wires and damaged light fixtures. Then, there is always a chance the heater will simply stop working and either overheat or overcool your aquarium water, killing the precious cargo inside.

That’s why it’s a good idea to:

  • Do your research thoroughly and purchase a top-quality heater,
  • Properly install the unit by following the directions in the manual,
  • Use a thermostat along with a temperature controller,
  • Regularly check all your aquarium equipment,
  • Have a backup heater in case one fails.


  1. Heater (aquarium), Wikipedia
  2. 10 Reasons Fish Make Good Pets, HuffPost
  3. Temperature Control, THF Magazine
Olivia Williams
Olivia is our head of content for, mum of one and a true animal lover. With 12 different types of animal in her family, it's never a dull moment. When she isn't walking the dogs, feeding the cats or playing with her pet Parrot Charlie, you will find her product researching and keeping the site freshly updated with the latest products for your pets!