How to Keep a Fish Tank Warm Without a Heater?


The most common option for heating a fish tank is often to turn to the use of a heater. However, if you aren’t using one, knowing how to keep a fish tank warm without a heater is key.

After all, regulating the temperature of a fish tank is a crucial part of caring for your fish. Not only is keeping your fish comfortable important, but it’s also important for regulating bacteria.

Luckily, if you don’t want or can’t have a fish tank heater, there are other options available. In this guide, we’ll help you find the best alternative for you!

Insulating the Fish Tank

The first thing to note is that insulating your fish tank isn’t a method to solely rely on. Yet, it’s a good addition to keeping any fishtank warm by using the other methods we’ll go over.

It’s even something that works for fish tanks of every size. Whether or not you have a full aquarium or a desktop fishtank, it’s worth insulating it.

The point of insulation isn’t necessary to add heat. Rather, the focus here is trying to trap heat in.

This means that it’s a great way to make other methods a little more effective. It’s also a good first step if your aquarium heater goes out and you need to trap heat inside quickly.

Measuring aquarium water temperature

There are a few ways that you can do this. The exact method you should use depends on your situation and goals.

If you’re working in a pinch and just want to create something quick, a blanket will do. This isn’t a long-term solution, though.

To do this, wrap the blanket around the aquarium but leave room for air to move around. Make sure you don’t get the blanket wet!

For something with more planning, you can also use styrofoam or similar insulation. Once again, these should go around the outside of the aquarium.

Expert Tip: Leaving your fish tank open at the top is crucial in this method. This way, you’ll still be able to access it for regular maintenance like feeding.

Warmth from Sunlight

This is a straightforward way to heat a tank without using a heater or any tools from an aquarium kit. The sun is, as is easy to tell, great at generating heat.

This means that if you want to keep your fish warm, putting the tank in the sunlight is a good start.

That being said, it isn’t a foolproof method. Unlike using an electronic tool like a heater or even LED aquarium lighting, it can’t regulate itself.

This means that you have to carefully monitor the temperature of the tank. Depending on the day, the temperature can fluctuate wildly.

The last thing you want is to put your fish in water that is too hot or too cold. If you’re using this method, make sure you have a thermometer handy that you check frequently.

If something is wrong with the fish tank’s temperature, you have to make sure that you regulate it as needed. This means that you might have to employ other techniques alongside using sunlight.

In other words, this is a labor-intensive choice that requires a lot of maintenance. It’s important to consider this when it comes to how much time you have to dedicate to your aquarium.

Heating the Room

This is probably the most effective method of heating a fish tank without relying on a heater. Heating the room the tank is in as a whole is the best way to ensure the warmth is constant.

Angelfish in home aquarium

However, depending on the type of fish you have, the room will have to be pretty warm. For instance, a betta fish will need a room with a higher temperature than 80 degrees.

This means that at least one room in your house will have to be dedicated to your fish this way. It can also wreak a little more havoc in energy usage than a heater alone.

Still, this is a great option for warmer climates or even warmer weather if you worried about energy consumption. This way, you won’t need to worry as much about heating it from the room’s unheated temperature.

Boiling Water

Stepping back to a short-term solution to heating a fish tank without a heater, there’s boiled water. Much like sunlight, though, this method requires a lot of maintenance and constant monitoring.

Because of this, boiling water is a method usually reserved for emergencies such as power outages or broken heaters.

For this method, you’ll need a container that can hold the boiling water – glassware and porcelain are great options. Make sure to clean them with dechlorinated water to remove any lingering soap residue.

Take your container and fill it about halfway up with boiling water. Then, place the container on top of your aquarium with one side more weighed down than the other.

Remember, don’t place the container against the flush sides of the aquarium. This will help to avoid impeding your fish or trapping them.

Employing a Low-Quality Filter

A filter can help you generate heat in your tank because they generate heat. You’ll want a low-quality filter for the job because they generate more heat.

cheap hob aquarium filter

Because this is a low-quality filter, it won’t quite do its job, though. Because of that, you’ll likely need to buy a larger filter than normal to make up for this.

The second problem with this is that it’s another example of a heating system that needs to be monitored. The temperature can fluctuate, so it’s good to keep a close eye on it.


When it comes to how to keep a fish tank warm without a heater, you have a variety of options. From adding insulation to employed boiled water, low-quality filters, and more, you have plenty of options.

Many of these options are a bit fickle, though, and require careful management. So, while you won’t need a heater, remember to keep a careful eye on the temperature in your fish tank.