3 Best External Inline Aquarium Heater


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Worried that an aquarium heater that sits inside your fish tank will mess up your decor? Well, you’re in for a treat! External inline aquarium heaters may be the just thing to end your worries.

An inline heater is installed on the outflow line of your aquarium filter, heating the water as it flows back into the aquarium. This is perfect for those who don’t want to clutter their tanks with heating equipment.

If you’re looking for an external inline aquarium heater, in this article I’m going to review the three contenders to the title of best external aquarium heater.

Benefits of External Aquarium Heater

As a crafty device, external heaters are essentially a more robust-looking pipe that features a heater element and a built-in thermostat that will switch off once the preset temperature is reached.

What can you expect from an inline aquarium heater? How and why is it better than an internal heater that sits in your aquarium? Here are just a few of the advantages of choosing an external heater:

Out of Sight

An inline aquarium heater will stay out of view and still heat your aquarium to the required temperature.

It’s even greater news for those with small aquariums, who don’t want their heater to take up extra space within the tank.

Not to mention how an aquarium heater can put a damper on a well-designed aquarium, something that aquascaping aquarists usually want to avoid.

Evenly Heated Water

A submersed aquarium heater may not heat up the water evenly throughout the aquarium. Usually, the water that’s close to the heater will be warmer than in other parts of the aquarium.

This isn’t the case with inline heaters, which heat the water as it flows back into the tank and it gets evenly distributed.

Easier Tank Maintenance

A traditional aquarium heater needs to be unplugged when carrying out a water change or tank maintenance tasks because there’s a risk of overheating when exposed to air.

With an inline heater, things are simpler and there’s no need to turn it off when you perform a water change.

There are, however, a few downsides to owning an aquarium heater, namely the fact that they’re dependent on your filter operating well and leaks can occur if you add extra equipment to the line.

For the most part, quality external heaters are also more expensive than traditional aquarium heaters, but if you want to save space or declutter your aquarium, they’re well worth the extra cash.

These risks are manageable, especially if you choose a quality aquarium heater and you set up your inline aquarium heater correctly. Let’s see how you should go about choosing your heater and setting it up.

How to Choose an External Aquarium Heater?

Like with any aquarium heater, you’ll need to make sure the heater you’ve set your eyes on is rated for the tank volume you have.

You’ll also need to look at the heater’s ability to sustain a precise temperature and that temperature fluctuations don’t exceed 2 degrees.

It’s also essential for your inline heater to have protection from overheating, which can happen if it runs dry for too long.

Therefore, make sure the aquarium heater features an automatic shut-off system or overheating protection.

Another important thing to look for is compatibility with your canister filter. You should check if the tubing or hoses that ship with the heater are compatible with your canister filter’s outlet line, otherwise, you will need to do a little tweaking.

How to Setup an Inline Aquarium Heater?

Even though your aquarium heater will come with an instruction manual on how to set it up, there are a few things that are worth reiterating when it comes to its setup.

The first important thing to remember is always install it vertically to avoid air bubbles and dry spots, which can crack the glass lining the heater.

Secondly, it’s always a good idea to also get a heater controller to avoid overheating your aquarium should the built-in thermostat fail.

An aquarium heater controller cuts off power to the heater once the pre-set temperature is reached acting as a fail-safe system should the thermostat fail.

Lastly, you should not attempt to install the aquarium heater on the inlet of your filter because debris and gunk can also build up in the heater, plus water has to pass through the filter first before it reaches your aquarium.

This can result in a loss of temperature, which, however minimal, can still affect the time it takes for the aquarium to heat up.

Best External Aquarium Heater

Now that you know what to expect from an external aquarium heater, let’s see the 3 best inline external heaters:

1. Hydor In-Line External Heater

The Hydor is a high-precision external heater that has a temperature swing of just 0.1 degrees, which is a remarkable feat compared to some traditional heaters and even some other inline heaters on the market. No wonder then that it’s at the top of my list of best external aquarium heater.

The heater is available in three different sizes with different hose sizes so you can pick the one that’s compatible with the tubing you’re already using.

Like I mentioned, it’s crucial to install these heaters vertically. Keeping them on their side or installing them upside down will cause air bubbles to accumulate in the temperature control, which can interfere with the heater’s ability to shut off when the preset temperature is reached.

The Hydor inline heater is perfect for terrariums, freshwater or marine aquariums. It can be used with aquariums up to 129 gallons.

Simply install it on the return line of canister filters. The system’s self-limiting PTC heating element offers protection against overheating.


  • Saves space in the aquarium;
  • Easy to install;
  • Keeps temperatures stable;
  • Overheating protection.


  • Pricey compared to traditional heaters;
  • A bit bulky, even though it doesn’t go inside the tank.


2. Feileng 200W/500W External Aquarium Heater

This Feileng external aquarium heater is another good example of a best-in-line external heater. It’s designed to be used with a canister filter but can be easily adapted for use with a sump pump too.

This heater features an automatic shut-off system for the event that the heater is left to run dry. The internal heat pump system prevents temperature variations.

If space in your tank is valuable to you or you simply don’t want it cluttered with heating equipment, this external inline heater is a great alternative, especially that it’s designed to fit most canister filters.

In this case too, be very careful to install the heater vertically, which the manufacturer expressly mentions in its product description.

Temperature is easily adjusted between 68-95 F. The system features LCD display for easy monitoring and use.


  • Automatic shut-off to protect from overheating;
  • Affordably priced;
  • LCD display;
  • Temperature control;
  • Compatible with canister and sump pumps.


  • Specs use the metric system (US customers will need to make conversions to figure out which model to use).


3. ISTA in-Line External Aquarium Heater

The Ista inline aquarium heater is a complex heater system that comes in various sizes and configurations, designed to match your canister filter perfectly.

Apart from canister filters, the heater can also be easily adapted to be used with dry/wet sump pumps and almost any scenario in which heated aquarium water is required.

As all external heaters, this too should be installed on the output of your canister filter. The manufacturer recommends using the attached loop to support the heater because canister filters are not designed for loadbearing.

The heater is designed for vertical use, so don’t attempt to install it on its side or upside down because this may cause issues as I explained above.

If the heater is left running dry for a short period, it automatically switches itself off to ward off any overheating issues.

The Ista heater features a thermal spraying glass, which speeds up the heating process and increases efficiency.

An auto power off safety system ensures that temperatures don’t exceed preset temperature or when there is a 5 degrees temperature difference between the sensors on the inlet and outlet. The heater will also switch off if water temperature exceeds 36 degrees (96 F).


  • Temperature variations are within 1 degree;
  • Automatic shut-off system;
  • Compatible with most canister filters;
  • Thermal spraying glass included


  • More expensive than a traditional aquarium heater;
  • Specs use the metric system.


These were my top picks for best inline aquarium heaters. I’ve chosen three heaters at three different price points to meet all budgets.


Overall, external heaters are an excellent solution if you don’t want aquarium equipment to clutter your tank either for aesthetic reasons or because of lack of space.

Quality aquarium heaters that are installed in-line tend to cost more than their traditional counterparts, but they’re a lot more convenient to use and install.

I hope you’ve found my overview of the best external aquarium heater contenders useful and you can now compare these heaters to traditional ones to make up your mind about which one would be best for you.

Updated: November 27, 2019
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