Aquarium heater guide. Its easy!

Aquarium heater is a simple device, however how many troubles you may have once it gets broken. They range from fishes boiled live to those frozen to death.

To avoid this disasters, I’ve selected the best models and reviewed them.

Aquarium heater is a device for maintaining temperature stable and for heating water or air in a terrarium. This is an important component of tank or terrarium technical equipment.

Water temperature is one of the crucial factors that influences on healthy existence of all living creatures in a tank.

Temperature parameters are especially significant for tropical and thermophilic fishes, which require temperature about 75-82°F (24-27 °C).

That’s why various models are used to keep optimal temperature to ensure healthy and comfortable living of inhabitants.

In winter heating is especially essential, since temperature may become lower than 68°F (20C°).

Such rapid temperature change may take a toll on inhabitants and in some cases it can even lead to fishes death. Abrupt temperature change is harmful for plants as well.

This is why temperature has to be the same in the whole tank. In the upper layers is always warmer, while in the bottom layers it is several degrees colder.

Recommended and acceptable difference between the bottom and upper layers temperature shouldn’t exceed 2С°. At that bottom temperature should be optimal for the tank plants.

How to choose?

You should follow the rules listed below:

  • Buy a device of required capacity
  • When buying you should also get a thermometer to check how it performs.
  • For large sized tanks it’s better to get not one high capacity model with a thermostat, but several devices of this type.
  • If the device is to be used in a tank with seawater, it is important to choose a device designed to brackish water.

What size heater do I need?

Tank SizeHeat 5ºC/9ºFHeat 10ºC/18ºFHeat 15ºC/27ºF
5 gal/25 L25 watt50 watt75 watt
10 gal/50 L50 watt75 watt75 watt
20 gal/75 L50 watt75 watt150 watt
25 gal/100 L75 watt100 watt200 watt
40 gal/150 L100 watt150 watt300 watt
50 gal/200 L150 watt200 watttwo 200 watt
65 gal/250 L200 watt250 watttwo 250 watt
75 gal/300 L250 watt300 watttwo 300 watt

The best models

I’d like to include more models into my review, but I assume that this would be pointless. All the models are quite alike, since it’s quite hard to invent something completely new.

Therefore, I’ve selected the top models according to their application – for large, medium and small sized tanks.

This list will help you to solve the problems yo­u may face with any kind of tank (both freshwater and saltwater ones).

Besides, below the list you’ll find some additional information, that will be of much help, if you don’t know which model to choose.

Aquatop Nano Aquarium

Aquatop company has a very strong position on equipment market and it continues producing high quality and stylish devices, that can be compared with such of German (Eheim) and Japanese (ADA) manufacturers.

This year Aquatop has introduced a super small sized aquarium heater for nano tanks from 5-20 gallons (like betta tanks), its capacity is 25W.

Owners of small tanks will surely like its size and ability to maintain temperature stable, LED display and possibility to put the device under the water completely.

Cobalt Aquatics Neo-Therm

This is another model for small and medium tanks, but it is manufactured using another technology.

This device is flat, made of plastic, it has an electronic thermostat which is accurate to ±0.5 ºF and includes a LED that displays Set temperature range from 66 ºF up to 96 ºF.

Eheim Jager 250W TruTemp

Eheim Jager 250 W (for smaller sized tanks they have Eheim Jager Submersible Aquarium Heater) – this is a heater with a thermostat. It was designed using the technologies: accuracy is 0.5° C and it adjusts from 18° to 34° C (65° to 93° F).

Eheim Jager can be drowned into the water completely, it has an embedded overheating protection in case if it is plugged in dry or if it falls out from the water.

It has a temperature control sensor and can be used for both freshwater and saltwater tanks.

The case is made of laboratory glass which is resistant to biological, chemical and physical influences.

Glass bulb of Jager heater is of improved quality, which increases the surface and ensures optimal and uniform spread of heat.

Thus, aquarium heater with capacity lower, than that of other brands, is capable of heating the same amount of water!

The lab glass was designed to be used in scientific experimental laboratories; it is manufactured according to a special standard including improved security of its usage as well as its composition shouldn’t contain any admixtures that could pollute water.

The glass is resistant to chemical and organic substances, it is shatterproof, it stands abrupt temperature change (for example, when getting under cold water during renew or sharp water level change when draining water from the tank).

Aqueon Pro Adjustable

Consider: Adjustable heat setting 68 to 88°F (accurate to +/- 1°), it doesn’t break, can be completely drowned, it turns off when overheated and has user-friendly plug-in indication system (the red indicator is on – the device is on, the green light is on – the device is off), lifelong warranty, made in the USA.

The device is available on the market with capacity from 50 to 250 Watts. I even don’t know what can be said on top of all above mentioned.

Thus, this aquarium heater has no rivals yet.

Finnex Deluxe Titanium Tube

If you have never had large fishes in your tank (like oscars, for instance), then you don’t know that these are quite capable of breaking an aquarium heater and they do it quite frequently.

You know what repercussions it may cause. Here is a solution for this issue – Finnex Deluxe Titanium Tube is designed right for large fishes.

What makes it different from analogue devices? It is made of titanium tube and covered with a special Protective Guard.

Even a human has to put efforts to break it, so for fishes it is almost unbreakable. Besides, this model is a very powerful one – from 300 to 800 W, which allows heating water in very large tanks (140-265 Gallons).

General information

It is essential to create proper environment for fishes, since most of them were brought from warm countries, that’s why they can live only at water temperature not lower than 25-30°C.

Even if the tank is located in a warm room it still requires an aquarium heater.

This is not only because the water should be warm, but also because its temperature has to be as stable as possible. Since some fish breeds are quite sensitive to abrupt temperature change.

Aquarium heater capacity is calculated in Watts. The manufacturers usually indicate on a packaging what size/volume is made for. Aquarium heater usually consists of two parts: heating and temperature control element to keep the temperature stable. The device may or may not have a thermostat. It is applied mainly for warm water and tropical tanks.

In modern aquarium husbandry electric heaters are more commonly used, they have coil heating element as a heating element.

In combination with temperature control elements ensure maintaining required temperature quire precisely considering their relatively small size and low price.

Depending on their location in the models are divided as follows:

  • internal, completely drowned into the water;
  • partially submersible, when the heating element is under the water and the temperature control element is not;
  • external, their heating element is in the open air.
  • Internal aquarium heaters are put either on a bottom, or in the place where there is a water flow from a tank filter or something like this. Most of the models have a suction cap that allows fixing the device to a glass wall of a tank or terrarium.

Submersible or non-submersible&

Are heaters fully submersible? Non-submersible heaters are the devices that are put under the water only partially, i.e. just their heating element.

As a rule the manufacturer indicates on the device case the maximum level till which it can be drowned. These models have their thermostat above the water level and you set the required temperature using it.

Submersible are very convenient in use since they can be put horizontally on a wall.

Such a location is especially convenient when performing water renew – you don’t have to take the heater from the tank.

When using submersible devices, first you have to unplug the heater when performing renew.

When draining water from the tank the water level will get lower and the glass tube with the heating element will stay out of water and it can just explode.

Most of modern models are already equipped with special thermostats, which help to avoid overheating. By means of thermostat you can set the required temperature, which is very convenient in every day use.

Also there are models without thermostats, they are programmed to maintain constant temperature and are more often used for small tanks, since they have low capacity. Heaters that have thermostats automatically adjust temperature. You’ll just have to set the appropriate temperature.

For example, when the temperature reaches the set value, the heater turns of. Overheating is impossible when using these models. In case if the device becomes out of order, the element will turn off automatically.

Ordinary models consist of a thermostat, contact elements and a heating spiral. Here the controls temperature and if necessary it closes and opens contacts, this way it turns the heater on or off.


Capacity is defined by the tank parameters (volume, surface square, presence of a cap or a cover-glass, the place of the location, type and power of light lamps etc.) and temperature difference, according which the device should heat the water.

In the most general case aquarium heater capacity is defined according to the tank volume and temperature difference from the range (0,2 : 0,5 W) / (l * degree).

For models with thermostat the relative capacity can be up to (1,0 W) / (l * degree).

As a rule, to heat 1 gallon of water (from 3,79 to 4,55 liters) it requires 5 W for 1 gallon. Thus, 20 gallons will require 100 W capacity aquarium heater. It is not recommended to get heaters with sufficient overcapacity, since if its control or heating element becomes out of order it may cause water overheating and death of aquatic organisms.

How to install?

The heater is a waterproof device and it can be installed both vertically – with adjusting handle above the water surface and horizontally – completely put under the water.

You mustn’t put the heater into the sand or gravels on the bottom. Water level should be always higher the minimal sinkage level, which is the mark MINIMUM WATER LEVEL, printed on the case.

You should always keep in mind that level decreases continuously due to its evaporation. The aquarium heater is fixed to the tank wall by means of a hanger with two sucking cups, which should be placed on the heater directly under its head.

The heater has to be mounted in some place in the tank with uniform and continuous water flow.

ATTENTION! Only 15 minutes later after installing in the tank, when the temperature of bimetal switcher of the heater becomes the same as the one of the water – this is when you can plug in your aquarium heater.


To ensure proper operation of the device it is significant to know how to mount and use heater. Here are the rules that will help you:

  • Make sure that the heater doesn’t touch sand or gravel on the bottom.

  • They should be mounted only vertically or horizontally, but if you have chosen the latter variant you should place the device on a tank bottom.

  • To avoid the device overheating and insure its better performance, it’s better to put it close to the tank filter. In this case the device will be constantly washed with the water flow.

  • Place the aquarium heater so, that on the chosen height the water level never gets lower than the “minimum” mark.

  • Owners of large sized tanks should be aware that the device shouldn’t be placed deeper than 90–95 cm from the surface.

  • Don’t plug in the aquarium heater if it’s not completely drown into the water.

  • After putting the heater into the tank, wait for 15–20 minutes till the device case temperature becomes the same as the water temperature. Only after this you can turn it on.

  • Don’t turn on if it’s out of service.

  • You should unplug (no matter if it is a common one or the one with a thermostat) when taking it out or putting it into the tank.

  • It is important to keep in mind, that while the device is operating you mustn’t put your hands into the tank or touch its walls.