Aquarium Heaters

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Most aquarium inhabitants are cold-blooded and so they are unable to regulate their own body temperature. In the wild, most are used to living in larger bodies of water where the temperature barely fluctuates at all.

When the temperature falls, fish’s immune systems begin to fail. They become prone to disease and illness and will often become lethargic and stop eating. If the temperature changes too quickly they can even die from shock.

To avoid these problems some kind of temperature stabilization in your aquarium is a must. This is why a reliable heater is crucial. I have spent hours researching some of the most popular heaters on the market and compiled this list of my favorites.

Recommended Aquarium Heaters 2020

Best All-RoundAqueon Pro Submersible Aquarium Heater

With so many unique and specialized designs on the market, making the right choice can be a little overwhelming sometimes. However, if you’re looking for simplicity and versatility then look no further. The Aqueon Pro has almost everything you’d look for in a submersible heater and all for a very reasonable price.

The device has an adjustable thermostat which is accurate to +/- 1° and ranges from 68 to 88°F. There is also an indicator light to let you know when the heater is working and when the tank has reached the set temperature.

Additionally, it has an auto shut-off feature that you don’t always see at this price range. If the product is removed from the water or if it overheats, it will automatically switch off and reset once the product has cooled down.

The Aqueon Pro is suitable for fresh or saltwater and in the manufacturer’s words, it is “nearly indestructible” making it suitable for even the most boisterous of tank inhabitants.

All in all, you’d be pushed to find an application in which the Aqueon Pro is not a great choice. and so I had no issues selecting it as my best all-around aquarium heater.

Best EconomyTetra HT Submersible Aquarium Heater

The Tetra HT is a no-frills yet high-quality heater that comes at a low price.

It has an inbuilt thermostat that maintains a water temperature of 78° F which is ideal for most tropical fish so you won’t have to worry about setting it when you first put it in your tank. It also comes with an indicator light to show whether the heating element is working or if the aquarium is already up to temperature.

Unfortunately, there is no auto shut-off feature (which is to be expected at such a low price). Just make sure that you have it switched off unless it is fully submerged.

The Tetra HT is designed for smaller tanks ranging from 2-10 gallons with 50-watt and 100-watt variants available. It is a fairly small device that can be mounted both horizontally and vertically making it easy to hide behind tank decorations and plants.

Overall the Tetra HT is a great choice of heater and ideal for those on a tight budget.

Best Digital – Fluval E Electronic Aquarium Heater

The Fluval E series is a very popular digital heater and has some great features.

The unit comes with a thermostat adjustable from 68 to 93° F and an LED display that gives accurate temperature readouts at a glance. The display can be changed between Fahrenheit and Celcius to suit your preference.

The temperature is measured using two different sensors which provide brilliant accuracy. Some claim that you won’t even require a separate thermometer anymore (being a belt and braces kind of guy I would still recommend having one though).

There are 2 different mounting brackets provided so that the display can always be easily viewed, no matter if the unit is placed at the back of the aquarium or to the side.

The LED display will illuminate in different colors depending on the water temperature at any given time. Blue for when it is colder than the set temperature, green for when the water temperature is as desired, and red when it is warmer than the set temperature.

Fluval E Series heaters come with an integrated fish guard and a safety shut-off feature for when the unit is removed from the water or if it overheats. 100, 200, or 300-watt models are available, making it suited for tanks up to 100 gallons.

The unit also has a low flow (LF) warning for when there is not sufficient water flow around the unit to distribute heat evenly around the tank. Some people complain about the sensitivity of this warning but I prefer this compared to other heaters which may just continue to heat only one side of the tank in silence and may even fail more quickly as a result.

Most DurableFinnex Hang-On Electronic Titanium Aquarium Heater

For a sleek, yet robust heater, look no further. This heater is one of the toughest on the market making it ideal for turtles and the like which may damage equipment inside of the tank.

With its titanium construction and corrosion-proof coating, the Finnex titanium heater has excellent protection against saltwater damage and is great for freshwater also.

The adjustable thermostat ranges from 70° F to 92° F with an accuracy of +/- 2° F.

One great feature of this particular heater is that the temperature can be changed via a control unit which is situated outside of the tank so no need to get your hands wet. This also means that turtles won’t be re-adjusting the temperature as they can do sometimes with regular heaters.

The unit is available in 100, 150, 200, 300, and 500-watt models. There is also a model that comes with a protective guard (click to check the price on Amazon) should you require one.

Best In-Line – ISTA In-Line External Aquarium Heater

In-line heaters are a personal favorite of mine as they provide even heat distribution throughout your aquarium, without any additional clutter inside of the tank. If you already have an external filtration system then an in-line heater is definitely the way forward.

Being fitted outside of the aquarium also means there is zero potential for boisterous tank inhabitants to do any damage.

The ISTA In-Line Heater is my top choice when it comes to in-line heaters. It is a very efficient and reliable unit that utilizes two thermal sensors that work in tandem to minimize temperature fluctuations. This is achieved by reading the water’s temperature both as it enters the unit and as it leaves the unit to re-enter the aquarium.

It has a variable temperature range of 68-95°F and the device gives a digital readout for temperature. Unfortunately, for US customers, this is only displayed in degrees Centigrade. However, this is easily converted to Fahrenheit with a quick google search.

The device has a number of safety features and will automatically shut off if:

  1. There is no water passing through the heater
  2. The temperature reaches 36°C.
  3. The difference between the two temperature sensors is more than 5°C.
  4. The water temperature exceeds the setting by more than 3°C.
  5. The water temperature drops below 3°C than the set temperature. The unit will also give a flashing warning signal to inform the user.

There are a few variants available. 150, 300, or 500 watts with 1/2″ (12/16mm hose) or 5/8″ (16/22mm hose) fittings.

Although I personally haven’t had any problems, there have been some reports of leakages around the hose fittings. This is a common issue with all in-line heaters and is in no way unique to the ISTA in-line. Most people say that this is easily resolved with the use of some regular hose clamps or even cable ties.

Nevertheless, the performance of in-line heaters is unrivaled which makes them worth the extra hassle and, in my view, the ISTA In-line is the best in its class.

Heater Size

For a rough guide on selecting the right heater size for your aquarium use the following table.

Aquarium Size RAISE TEMP
5° C / 9° F
10° C / 18° F
15° C / 27° F
5 Gallon/25 Liter25 watt50 watt 75 watt
10 Gallon/50 Liter 50 watt 75 watt 75 watt
20 Gallon/75 Liter 50 watt 75 watt 150 watt
25 Gallon/100 Liter 75 watt 100 watt 200 watt
40 Gallon/150 Liter 100 watt 150 watt 300 watt
50 Gallon/200 Liter 150 watt 200 watt 2 x 200 watt
65 Gallon/250 Liter 200 watt 250 watt 2 x 250 watt
75 Gallon/300 Liter 250 watt 300 watt 2 x 300 watt

It should be noted that the effectiveness of some heaters may differ even at the same wattage so it’s always worth referring to the manufacturer’s specifications.

For larger aquariums, two smaller heaters will provide better heat distribution and reduce strain compared to having a single larger heater. Another positive to this is that two smaller heaters that are not able to fully heat the aquarium alone will not cause as big of an issue should one overheat. At the same time, if one was to shut off entirely, you have a backup and the impact will not be as severe on your fish.

You should always check the temperature of your tank with an independent thermometer at least once daily as no heater is exempt from failure.