Hydor Inline Heater Review (Best External Aquarium Heater For Today)

The Hydor inline heater is one of the top aquarium heaters in the market. Whether you make a self-sustaining aquarium, a biotope aquarium, or a generic one, at some point, you’ll feel the necessity for a heater. An aquarium heater helps to achieve and maintain the optimum temperature for your fish to flourish.

This Hydor inline heater review aims to let you know its features, pros, and cons in detail. You’ll get an honest overview of the product & then decide whether you should choose it.

The heater I am talking about is an external type heater. However, there are other types like submersible or semi-submersible. I choose an external type heater to review since there are some benefits of this sort of heater over others.

External heater doesn’t clutter an aquarium with gears inside since it mounts outside, so you don’t need to sacrifice your aquarium’s aesthetic appeal to set up a heater. Moreover, you’ll get a constant temperature and a much better heat distribution with an inline external heater than a stand-alone one.

200 Watt - 1/2 Inch Hose
200 Watt - 5/8 Inch Hose
300 Watt - 5/8 Inch Hose
Hydor ETH 200 In-Line External Aquarium Heater,...
Hydor ETH 200 In-Line External Aquarium Heater,...
Hydor ETH 300 In-Line External Aquarium Heater,...
200 Watt - 1/2 Inch Hose
Hydor ETH 200 In-Line External Aquarium Heater,...
200 Watt - 5/8 Inch Hose
Hydor ETH 200 In-Line External Aquarium Heater,...
300 Watt - 5/8 Inch Hose
Hydor ETH 300 In-Line External Aquarium Heater,...

Inline heaters are electric heaters, which heats the fluid instantly that flows through them. In an inline aquarium heater, liquid (water) circulates in a closed-loop until it reaches the desired temperature.

The thermostat sensor measures the temperature and controls the heating. An external inline heater must be installed on the filter’s outlet line; water gets heated while it flows back to the aquarium through the heater.

There are two models offered by the company. One is a Hydor 200 watt inline heater, and the other one is Hydor 300 watt inline heater.

Hydor 300W inline heater is rated for 80 gallons, meaning you can heat as big as an 80 gallons tank. It only fits with the tubing of ⅝ inch. You just need to cut the tube into pieces and joints on the two ends of the heater.

The Hydor 200w inline heater is for use in as large as 60 gallons tank. It offers two different diameters, ½ inch and ⅝ inch. So, you have the option to buy, which is suitable for your filter hose diameter.

Hydor inline heater sizing

∆: The difference between the set temperature (required temperature) and the minimum temperature in the room.

Always buy a heater for an under or specified size of the tank. This may help you get optimum heater performance and long-lasting service. Don’t install a heater for a tank that is oversized for the heater.

Buying Hydor 200W inline heater for heating 80 gallons (which is not recommended) will take longer to heat the tank & will function with lesser efficiency. This suggests the heater presumably won’t last long. 

Higher wattage means higher heating power. The wattage requirements depend on the water volume and the difference between the room temperature and the tank’s desired temperature.

The unit makes an audible click sound when it turns on and off each time. Obviously, it’ll make less click noise if it has to turn on and off less frequently. More click sounds are often monotonous if your aquarium is located in a quiet place. Selecting the proper size heater can alleviate this little problem too.

You always have the option to modify the filter hose to match the heater diameter size. But, If you don’t want to take the extra hassle of altering your canister filter hose, select the heater in between available sizes that exactly match your hose size. Otherwise, you have to opt for modification of the filter hose.

In this Hydor external heater review, I’ll discuss the heater’s different features, which I found most handy for the fishkeeper. The most important features to look at in a heater are the safety features and its reliability. Let’s have a look at what this Hydor inline external heater offers.

The manufacturer claims it’s the first of external heaters with advanced PTC (Positive Thermal Coefficient) technology, which will keep you tension-free in terms of overheating. This self-limiting heating element also ensures long-lasting service life.

With the PTC technology, the traditional resistor coil is replaced by a conductive ink deposited polymer sheet. This conductive heating element is wrapped inside a glass tube and heats the water while flowing through it.

The feature that nearly all fishkeepers like in a heater is the automatic shut-off option. Meaning the heater will shut itself automatically when it reaches the set temperature; otherwise, it may spoil up cooking all of your efforts in the aquarium.

PTC technology improves the safety and efficiency of the product. It enables uniform heating and eliminates the probability of overheating by self-regulating to a designed temperature.

The safety also has an automatic shut-off when it runs dry. But, for this instance, you need to be a bit cautious. Since it’s glass inside, with any glass that’s heated and if suddenly exposed to cold water temperature, there’s a possibility that it may crack or break. But, you can prevent snapping with little extra care.

Before circulating water again, give a while to cool down the heater. Afterward, start the water flow, let it for some time, and then activate the heater. In this way, you can extend the lifetime of any glass-made electric heater; as you know, electric appliances stay longer if you handle them well.

The glass won’t break in regular use, only when it’s not installed correctly & utilized in a way it’s not designed for. If glass breaks, you’ll see a noticeable water leak.

Hydor inline heater for fish tank review

This external inline heater fits with almost all the canister filters like Fluval canister, EHEIM canister, etc. It is also easily adaptable with sump pumps (wet/dry).

But, you may have a filter hose that doesn’t match with the heater dimensions. You can still use it if you have a filter hose that is ribbed or smaller/larger diameter than this heater size. It would help if you modified the hose to splice into. For this, you’ll need some adapters, clamps, etc. Local hardware stores can help you to do so.

The full range of temperature settings is 62°F – 94°F. You can set whatever temperature you would like for your heater to maintain within this range. The good part is outside of the heater won’t get hot.

It doesn’t instantly heat the water but is quick enough to boost the temperature and most significantly maintains that within the 0.2 ~ 0.5-degree range. Therefore, just set and forget. It’ll keep doing an excellent job of keeping your fish safe and comfortable.

There is a red light indicator, red light glowing means the heater is on. If that’s off, it’s at the set temp. Just to let you know, as you can’t guarantee electrical equipment, if the red light is on and the water isn’t getting hot enough, it may be a sign of heater burnout.

Conversely, users mentioned it has a long service life. Some are using the same heater for nearly 5-10 years so that you can think of burnout as a rare phenomenon. The maker provides 02 years warranty; within this period, they will fix it free of cost if your heater gets faulty under normal use. An excellent, responsive customer care service is in place to serve all of your needs.



  • Easy to put in and use
  • Precise temperature control, safe and UL listed
  • Automatic shut off to prevent overheating.
  • Proper heat distribution throughout the tank.
  • Usable in both fresh and marine water.
  • Long-lasting service under regular use.
  • Two years warranty.


  • Some may find the click sounds boring.
  • Not waterproof, it can be inoperable if it’s exposed to water.
  • Not useable with filters except canister and sump pump.
  • It is quite a bit expensive.

Unlike other aquarium heaters, inline heaters do not stay inside the aquarium tank. Typically an inline heater and a canister filter/sump is the only possible combination. You’ll have to install the inline heater at the discharge line of the filter.

When water returns to the tank, it passes through the heater. The heater heats water to a preset temperature. The tank water gets warmer. A built-in thermostat shuts the heater when the water temperature reaches the preset point.

After a while, the heater starts again when the water temperature drops. And this cycle continues.

Obviously, you don’t want to call a plumber to install simple equipment like a heater. Yes, you don’t need to, since installation is straightforward, not so cumbersome; get the hose ready and follow the step-by-step guideline.

The heater is unidirectional, only allowing flow in one way. A flow indicator on the body indicates the direction of the water flow. Confirm the heater is pointing in the same direction as the water flows into the tube.

The Hydor inline heater needs to be installed in line with external canister filters or sump pump. You must place it on the return lines, ensuring the water entering the heater is freed from dirt and debris. With the tube hose, cut into pieces and splice into both ends of the heater. Each lot has connectors and sealing gaskets designed to clamp the filter hose snuggly. 

Tips: It is designed in such a way so that it’s not possible to see inside, whether it’s clogged or not. Therefore, to stop it from clogging up quickly, you must always connect in the return line, i.e., the filtered water line. If it’s clogged, you’ll notice a significant drop in water flow, and then try cleaning your inline heater with a pipe cleaner.

Ensure the heater stays in the vertical upright position. It must remain upright as per the manufacturer’s recommendation. Also, make sure the heater is adequately supported to avoid stress on the canister filter’s output assembly since those are not designed to bear weight.

Tips: There is a problem with the horizontal position, although the heater will heat if the water is flowing through it. However, the thermostat temperature controller may malfunction since it can collect tiny air bubbles. 

Reminder: Although this heater is built to heat the water, you’ll wonder to know, it’s not water-resistant! In exposure to water, it may become non-functional. So always keep the heater far away from water and never immersed there.

If you think a video demonstration would be helpful, you can watch the video as well.

No, it doesn’t make any other noise usually, since there’s no moving part. If you hear any noise, thoroughly inspect the heater for any loose, broken, or other notable damage.

Yes, there’s just one difference, and that’s the rating, 200 W is meant to heat efficiently 65 gallons, and 300W is for 80 gallons.

No, this is only made by aiming to use inline with a canister filter or sump pump. It isn’t usable with a sponge filter since there’s no water movement. It requires water movement inside; otherwise, air bubbles will accumulate and make the heater inoperable.

You may have heard horror stories about overheating and burning out all the fishes, but this heater works perfectly. If that happens, it can occur with any heater.

Still, if you would like to be extra cautious or add more safety backup, I’ll suggest you purchase an additional temperature controller to regulate the heater. If one fails, the other will keep you safe.

If you are confused over getting an inline external heater, go for it. You won’t be disappointed! Hydor is a reliable brand; it is a bit costly compared to other heaters, but it’s affordable. It would be best if you did not skimp on vital equipment like a heater.

2 thoughts on “Hydor Inline Heater Review (Best External Aquarium Heater For Today)”

  1. These are out standing solution to getting your heaters out of your tanks. I keep large cichlids of all kinds and they are allways smashing heaters, or just a pain when cleaning tanks in side the tank so i touch the plunge a few years ago. And first put one of these on a 65 gallon with a eheim cannister. i have sence used them on many tanks never have had any issue with long term use with them. I never used with a heat controler and allways consistent temp. Now i have 2 200 w 1/2 version on a 75 gallon with a sump on the return with a inkbird wifi controler and works amazing this way as well. As stated they are pricey for sure but worth the money. GO FOR IT


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