Aquarium Heater – What You Need to Know Before You Buy One

If you want to know more about fish tank heater and how to use them, you are in the right place.
An aquarium heater is exactly what you think it is – a heater that warms the water of your aquarium.

The aquarium heater not only creates the right water temperature for your fish, but it plays a critical role in keeping that water temperature stable.

Most tropical species enjoy water that is around 74-82F or 23-28C.
It’s almost impossible to successfully maintain a water temperature at this level unless you are actually living in the tropics.
And even then, there are variables that mean your tank will struggle to keep a stable temperature through a 24-hour period.
That’s where water heaters come in.
Unless your aquarium has a steady water temperature set at the right level, your fish can suffer health problems.
Just like Goldilocks and the three bears, things must be just right for your fish to thrive.
If the water temperature is too cold, your fish can become sluggish and stop eating.
Without correction to the temperature, they could even freeze to death.
And of course, if the water temperature is too hot that is just as bad – aquarist forums are full of owners warning about the dangers of an overheated tank and a slew of dead fish.

There are a lot of facts to take into consideration when purchasing a water heater for your aquarium – the size of your tank, the kind of species you will stock, the dimension and situation of the room the tank will be in – it’s a lot to take in. A light 50w water heater? A high-powered 200-watt aquarium heater?

In this article, we’ll cover everything you need to know about aquarium heaters.
From the factors you need to take into consideration through to determining the right size and aquarium heater, we’ll cover it all.
We’ll also look at the different kinds of fish tank heaters that are available, and review products from the most popular aquarium heater categories so that you can make the right decision based on your own circumstances.
Let's dive into it!

There are plenty of online formulas to help you choose the right size water heater for your aquarium. But always remember that these formulas are just a guideline.

There are also plenty of other factors you will need to be aware of to ensure that the water temperature in your aquarium is both adequate and stable.

Using a water heater in your fish tank isn’t a set-and-forget proposition. Like all equipment, heaters can malfunction or break, potentially overheating your tank (and fish) or not keeping it (and them) warm enough.
To avoid the heartbreak of a tank full of dead fish, it’s important to think about these issues:

There are numerous different kinds of water heaters that you can buy for your aquarium, although there are four that are the most common.

There are other kinds of heaters as well, such as in-pump heaters, hanging heaters or heating mats that sit underneath a tank. While many of these other varieties work quite well, heating mats aren’t recommended. This is mainly because if they malfunction or stop working completely, you need to drain the tank entirely to be able to move it to fix or replace the mat.

Submersible heaters are designed to be placed into the water of your fish tank.
They are generally long, slender and round, like a stick or tube.
They attach to the walls of your aquarium with suction caps or clips and they can be placed horizontally, vertically or at an angle.
It’s important to keep this kind of heater off the gravel though, as gravel doesn’t conduct heat well and it could cause the glass of the heater to crack.

Because this kind of heater lives entirely within the water, it’s generally more efficient than a hanging aquarium heater, which attaches to the side of the tank and has an element below water.
A submersible heater can be placed low into the water, and if it has an internal thermostat it usually works best if you put it horizontally.
This will help the thermostat read the water temperature correctly and switch the heater on and off at the right times.
If Submersible Heathers are your choice, there are two models we particularly like that you can check out on Amazon:

The Aqueon 50W Pro Heater is a fully submersible heater and top seller across the board, highly rated for its functionality, reliability and performance.
It works in both freshwater and saltwater aquariums and has the great feature of being completely shatterproof as there is NO glass in the construction – it’s made from aluminium.

Another very popular heater is the Fluval E Aquarium Heater 100W.
The Fluval E Heaters are technologically advanced and have a clear LCD display that shows real-time water temperature.
This LCD panel changes colour if the aquarium water temperature varies from the temperature you’ve set, so that you can take immediate action to remedy any issues.
If the water temperature rises or falls quickly, the coloured screen starts to flash in order to grab your attention.

This kind of heater consists of a glass tube with a heating element wound around a ceramic or glass insert.
Some of these heaters also contain sand, and most of them are fully submersible – that is, they can be placed entirely underwater.
Others are known as hanging heaters, which hang from the top or side of your aquarium but can’t be completely submerged – they have a clear water line marked and you must make sure not to put the heater any lower into the water than that.
Some of these heaters are immersible only to the water line marked on the unit, but they do also manufacture fully submersible versions such as the EHEIM Jager Aquarium Thermostat Heater, which come in models from 50W-300W. Check out more reviews.

Also known as cable heaters, substrate heaters use a flexible cable with a heating element, usually buried underneath the aquarium sand or gravel, which has the added benefit of completely hiding the heater.
This kind of cable heating is the least common kind of aquarium water heater.
Some aquarists believe that substrate heaters are best for planted tanks, where the gravel can tend to keep plant roots cooler than is ideal for growing conditions.
The cable or wire of the heater becomes warm and heats the gravel, which then radiates the heat and warms the water.
Because the heater keeps the gravel warm, it also keeps the plant roots in a comfortable condition.
It’s best to place these in a zig-zag formation so that you are heating your substrate evenly.

In some cases, you can buy an aquarium filter that has the added benefit of a built-in heater element. These tend to be canister or power filters. These filters perform the double action of heating the water as it goes through the filter, so that they return not just clean water to the aquarium, but water that’s warm as well.

When you are adding a heater to your aquarium there are four key things to remember.

So what size of heater do you need for your aquarium? 50 watts? 75 watts? 200 watts?
There are many different factors to take into consideration, and a range of different formulas you can use to help you choose your aquarium heater.
It’s generally accepted that for every gallon of water you have in your aquarium, you should use between 2.5 and 5 watts of heat.
However, this rule is need to be taken with some grain of salt, especially with large tanks, which lose heat more slowly than smaller tanks.
And smaller aquariums will only need small heaters – a 10-gallon tank for example, will typically need a 25-75-watt water heater, while a 70-gallon tank will need an aquarium heater between 200-300 watts.
But very small tanks can be a real challenge to heat – you may need to choose a miniature option like the Tetra HT Submersible Aquarium Heater that you can check on Amazon or avoid heating altogether.

You also need to think about the temperature of the room your aquarium is in, along with the temperature you want in your tank.
What’s the starting temperature of the room you have your tank in?
If your room is usually 75F and your fish only need 78F, then you’ll need a much smaller heater than someone whose tank is in a very cold room.

Online forums are also a good place to go for questions.
There are plenty of different online guides you can use to help you with these calculations:

Here is a table with guidelines for typical aquarium heater specifications:

In this article, we’ve outlined some of the many variables that you need to take into account when thinking about Aquarium Heaters for your fish tank.
As human being you know well how a change in the temperature can affect you. For your livestock it can be even more massively critical.
We have given you all you need to take into account to manage wisely the temperature of your tank using a heater.
From type to room dimensions to the kind of fish you’ll stock, all the way through to size of the tank and the ambient temperature of your home.
Don't stop researching: speak to other fish owners, get onto the forums and run all the issues to ground before you buy your heater that suits your own tank needs.
It’s worth it doing it, and your fish will thank you in the end.
Let us know in the comments how you are doing with your heaters and if you have any questions.
Happy fish keeping!