Aquarium Heaters Guide

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

what are Aquarium Heaters?

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.

Last update on 2024-07-20 / Affiliate links / Images from Amazon Product Advertising API

Heaters are a fundamental piece of equipment particularly if you have tropical livestock.

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.

Preview Product Rating Price
Eheim 3619090 Jager Aquarium Thermostat Heater 300W, Black Eheim 3619090 Jager Aquarium Thermostat Heater 300W, Black No ratings yet $35.69Amazon Prime

Last update on 2024-07-20 / Affiliate links / Images from Amazon Product Advertising API

what kind of heater do you need?

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!

What are the things to take into consideration?

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.

  • What kind of fish are you stocking?

    What kind of fish are you stocking? Some species, like neon tetras, guppies, angelfish and bettas, like their water to be toasty warm and highly stable all the time. Others, such as barbs or swordtails, are a little hardier and can tolerate some changes to their water temperature.

  • Tank size

    If you have a big tank, you might need to think about installing two smaller heaters to warm the water consistently. Consider putting these heaters at opposite ends of the tank to ensure proper heat coverage.

  • how many heaters

    Many aquarists also recommend using more than one heater if you choose a hang-on or submersible heater. This means you have a back-up if one fails, and will help to ensure your fish don’t get a shock from water that rapidly cools around them. Tropical fish are especially susceptible to changes in water temperature. If the water temperature fluctuates by even a few degrees – for example, if it’s warm during the day but then cools at night – this can cause problems for your fish.

  • heater tube

    Make sure your heater tube length matches the height or length of your aquarium. Heat rises, so you need to make sure you’re covering the full length and depth of the tank. And how thick are your aquarium walls – that is, how quickly will it lose heat to the air surrounding it?

  • the positioning of your tank

    Think about the positioning of your tank. Is it in a big room that’s hard to keep warm, or a small room that stays toasty? Is it by a window that gets direct sun, so that it heats up during the day but then cools at night? Is it underneath or near an air-conditioning vent that might cool it too much? These are all things that can affect the stability of the water temperature in your aquarium. It’s a good idea to check regularly so that your tank is providing the optimum temperature for your fish.

Things to be careful of when using a water heater in your aquarium

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:

  • It’s better to buy a high-quality heater once.

    Heaters are the kind of equipment where quality really counts. Don’t succumb to the temptation to buy a cheap unit that you have to replace time and again – not to mention replacing the fish and other animals that could suffer when it breaks. Consider this a proper investment in the health and safety of your tank and your pets.

  • Read the instructions.

    Too often, we just go ahead and do something without reading the instructions. Do you know how to clean your heater to avoid salt pollution? Have you set everything up exactly as it should be? The instructions are there for a reason.

  • Check the temperature of your tank with a thermometer.

    Even when you have a water heater functioning in your aquarium, you should regularly check the temperature of your water. It’s an essential part of good tank maintenance and it can help you to spot any issues before they become more serious. Thermometers don’t have to cost a lot of money – but they can save you a lot.

  • Consider installing a temperature controller.

    Are you often away from home, or not able to regularly check your water with a thermometer? You can buy a special controller that automatically monitors and controls the temperature, and alerts you if something needs attention.

What type of heater should you buy?

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

Each of the four common types of heaters performs the same function – heating the water and keeping the temperature stable – in a slightly different way, using different features.
Any one of these could be the right choice for you, depending on the kind of tank and fish you are running.

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

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.

Immersible heaters

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.

Substrate heaters

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.

Filter heaters

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.

Four things to be mindful of

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

  • When you first get the heater, it’s important to let it acclimate to the current temperature of your tank. Sit it in the water, with the heater properly set up, for a good period of time – at least an hour – before you plug the heater in or set the thermostat. This will help to stop the glass getting shocked by a difference in temperature and possibly breaking when the heater element comes on.

  • You should do the same thing in reverse when you’re removing a heater from your aquarium, so that the heater element cools down properly. The last thing you want is for your heater glass to break and contaminate your tank. That could seriously hurt your fish, not to mention that it also means a full tank drain and clean. It will also stop the heater from melting any surface you might put it on after you’ve removed it.

  • When you put a water heater into your aquarium, make sure the glass of the heater isn’t touching the glass walls of the tank – or gravel, or an ornamental item inside. Again, this can cause the glass to break, potentially killing your fish through electrocution. You can buy inexpensive heater guards to protect your tank against this possibility.

  • When your fish tank heater is set up inside the aquarium, ensure that your fish can’t get caught between the heater and something else. You want to make sure that there are plenty of places – ornaments, or plants – that your fish can hide in, so that they don’t have to use the heater as a hiding place of last resort. This can hurt and burn your fish, and it’s not good for their wellbeing either. Fish can be shy, and they need plenty of places that they can hide in to feel safe. A heater is not a safe thing for a fish to hide behind!

How to determine the best size of aquarium heater

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.

Subtracting the average room temperature from the temperature you want your aquarium water to be, should provide a good guideline.

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:

Watts Tank Size
50 7 - 15 Gallons
75 15 - 20 Gallons
100 20 - 40 Gallons
150 40 - 75 Gallons
200 75 - 105 Gallons
250 105 - 150 Gallons


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!

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