How To Keep A Fish Tank Warm Without A Heater – 8 Helpful Solutions

Having two fish tanks in the space of three years made me realize that all fish have a preferred temperature range. The preferred temperature is usually between 65°F (18°C) and 85°F (29°C). These are the temperatures that fish thrive in and therefore are beneficial for breathing, feeding, reproduction, and more. But you may be wondering how to keep a fish tank warm without a heater.

There are various ways to warm your aquarium’s water temperature without using a heater. Making use of a smaller tank, moving the tank to a warmer area, and insulating the fish tank’s glass are some of the many ways you can keep the fish tank warm. In addition, using some of these methods will ensure that the fish survive even when there is no heater. 

8 Ways To Keep A Fish Tank Warm Without A Heater

The survival of fish depends on your ability to maintain a stable and constant water temperature. Keeping the water temperature becomes challenging when there is no heater. The temperature outside the tank significantly affects how quickly the temperature warms up and cools down. 

Below are eight ways you can keep your aquarium warm without a heater:

1. Use A Heating Mat 

A heating mat is one of the ways in which you can keep your tank warm without a heater. This method is usually used by people who own smaller fish tanks. A heating mat raises the water temperature in the fish tank but also acts as a protective layer against cracks. However, this method will be less effective on larger fish tanks; therefore, another method is required. 

2. Use A Heavy Towel Or Blanket

A heavy towel or blanket is a quick method that you can use to ensure that your fish tank is warm without a heater. This method is used for smaller fish tanks but can also be used for larger fish tanks. Using a heavy towel or blanket helps to avoid cold air that might find its way inside the tank. The aim is to keep water temperature constant and stable.  

3. Use A Lid To Cover The Fish Tank

Using a lid, hood or canopy is the perfect way to maintain the water temperature of the fish tank. This method is considered the easiest and most common way to keep their fish tank warm without a heater. This method limits water contact and reduces the chances of cold air entering the fish tank. 

Using a lid, hood or canopy also helps reduce unwanted elements in the air that might affect the fish. This method is an easy way to access the fish tank without affecting the water temperature too much. However, using this method can potentially reduce oxygen supply which can negatively impact the fish’s survival. 

4. Use Warm Water 

Using warm water for your fish tank is a short-term solution to keep your fish tank warm without the use of a heater. This method helps maintain the water temperature but requires you to monitor and pay close attention to the fish. Never add boiling water to the fish tank; instead, mix the boiling water with room temperature water before working it in the fish tank. 

5. Place The Fish Tank In A Warmer Room

One of the most popular methods to keep a fish tank warm is to move it to a room with a warmer temperature. This method keeps the water temperature stable and usually does not require much effort. No or little heat in a particular room may cause fish to become weak because of the water temperature fluctuation. 

If you are unsure which room is warmer, I suggest moving the fish tank to a spot where there is direct sunlight. This will keep the tank warm without the use of a heater. Remember to always check up on how your fish reacts to direct sunlight. This is an effortless, easy and inexpensive method you can use when you need to warm up your fish tank. 

If there is no good spot for the fish tank, then make sure to get a set of lights to keep the tank warm. These lights need to be strong enough to heat the water when there is no heater. The best option would be to get fluorescent lamps or LED lights. In addition to the lights, you may even want to get a timer that turns the lights on and off throughout the whole day. 

6. Make Use Of A Smaller Tank

Smaller fish tanks, or even nano aquariums, are best for people experimenting with an aquarium system for the first time. These tanks tend to heat up much faster and help maintain a constant water temperature. This method is considered the best when you do not have a heater or when your heater is not functional. 

7. Get Some Coldwater Fish

Coldwater fish are the perfect type of fish to get if your fish tank does not have a heater. These fish tend to survive and thrive in cooler water temperatures. They are also known for resisting water temperature fluctuations, which tend to happen frequently. Setting up a fish tank without a heater results in fluctuations; therefore, getting coldwater fish would be ideal. 

8. Use Insulation For The Glass Wall Of The Fish Tank

Using insulation around the glass walls of your fish tank would be the next best thing to do after you find an acceptable water temperature. This method prevents the warm temperature from escaping the fish tank. The negative thing about this method is that you will need warm-water changes more often than usual. 

Some people believe this method may not appeal to the eye, but it certainly helps trap the heat inside the fish tank. This is inexpensive and easy to use when your fish tank does not have a heater. Insulating the back and sides of the fish tank will keep the water at a stable temperature, allowing your fish to thrive. 

Why Is It Important To Keep A Fish Tank Warm?

When you are setting up an aquarium for tropical fish, concerns about temperature should be at or near the top of your list. People who experimented with aquariums know that monitoring the water temperature is important for the survival of the fish. The rapid change in water temperature is usually why fish become weak. In addition, these fluctuating water temperatures cause fish to become stressed and eventually die. 

Fish are cold-blooded and, therefore, cannot regulate their internal body temperature; their body temperature changes when the water temperature changes. 

Below are some of the reasons why you would want to keep your aquarium at a warm temperature:

Body Temperature

This is an essential factor for a fish to survive. The water temperature allows fish to thrive and survive. The body temperature of a fish is similar to the temperature of the water. Hence, they are hugely affected by the shift of the water. The water temperature can potentially hinder the life of the fish. 

The water temperature in the fish tank affects the health and growth of the fish. Maintaining the temperature can help reduce illnesses and weaknesses. Lower water temperatures prevent new plants’ growth at the fish tank’s surface. Therefore, you must constantly monitor the tank’s water temperature so the fish can live healthily. 

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Fish breathe by flowing water into the mouth and forcing it through their gills. This process allows fish to absorb oxygen and release carbon dioxide into the water. However, as the temperature alters, the water’s oxygen level decreases, which can be problematic for the survival of the fish. 

Fish tend to experience breathing problems when the water temperature becomes critical. Therefore, it is necessary to maintain warm water temperatures when experimenting with an aquarium system. Warm water allows fish to breathe efficiently and contributes to their survival.

How To Keep A Fish Tank Warm Without A Heater


The water temperature in a fish tank plays an important role in the reproduction process of fish. Each species of fish has its requirements for water temperatures regarding reproduction. If your fish tank does not have a stable water temperature, it becomes difficult for the fish to reproduce. 


Fish are more likely to feed if their body has a stable water temperature level. The functioning of the metabolism, oxygen demand, and activity of the fish tends to be more healthy when there is a constant water temperature. This encourages the fish to feed more and, eventually, leads to the survival of the fish. 


Water temperature is closely tied to the health and wellness of your fish. If you are not able to incorporate a heater into your aquarium setup, hopefully these solutions for how to keep a fish tank warm without a heater will help you manage your fish’s environment and keep them happy and healthy.

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