How To Keep A Fish Tank Warm Without A Heater

How to keep a fish tank warm without a heater? Sometimes aquarists ask the question, and I’ve come up with a detailed answer here.

If you want to grow your own fish, but don’t have the money or space for an expensive heater (or simply cannot be bothered), keep them warm without one! Here’s how.

Case-1: You Don’t Have A Fish Tank Heater At All

These instructions will show you how to set up a heater-free tank that won’t require constant attention to keep the water temperature stable. I hope with this easy setup, you’ll not have to worry about your aquarium water temperature. 

Later on, I’ll talk about emergency circumstances!

You Don’t Have A Fish Tank Heater At All

1) Increase The Temperature In Your Home:

The fish tank temperature depends on the surrounding temperature naturally. So if your home temperature is warm enough, your aquarium will remain at a higher temperature.

You can keep your tank warm without a heater by warming up the room where it’s kept. Raising the room temperature is an excellent first step, and this may be enough for certain types of fish in small nano tanks!

This tip could also work with larger standard aquariums if you place the aquarium in a warmer part of the house or near a heater.

2) Select A Warmer Location For The Tank:

Any home has colder and warmer zones, which you can take advantage of if you don’t want to use your heater. Setting up your aquarium in a hotter location will gain you a few degrees without adding any additional work.

Here are some things to look for while deciding where to put the tank:

  • No drafty areas! Even if you have a central heating system, drafty locations tend to be cold. So, the cold air coming in can lower your tank’s temperature, making it harder to stay warm.
  • Moving your aquarium to a higher level in your home in a multistory house can make a difference of at least a couple of degrees, as upper floors tend to be much warmer.
  • Finding a location in your home where your tank can receive at least 4-6 hours of natural sunshine each day is perfect, and you’ll be surprised how quickly a nano tank can warm up without any further input.

(Have some algae-control procedures on hand if you go the warmth-by-sunshine method, as algae development can surge when there’s a lot of sunlight pouring in.)

3) For Water Changes, Use Warm Water:

Water changes regularly with warm water can assist you in bringing the tank’s water temperature to the desired level without using a heater.

 It is important to gradually increase the water’s temperature. Some species may not like a sudden jump in temperature. To avoid any potential stress or discomfort on these delicate creatures, perform hot water changes very slowly!

If you use this method to warm up your tank, remember that you’ll need to save the extra water for water changes. 

Remember that you should never put boiling water directly into your tank.

4) Use A Tank That Isn’t As Big:

If this is your first time trying an aquarium system without a heater, nano tanks are ideal. They heat up quickly and maintain a consistent temperature with minimal effort on your side once set up.

However, the water in a smaller tank will be colder quickly in chilly weather conditions or in a power loss, but damage management is much easier to maintain than with more extensive arrangements.

5) Your Tank’s Glass Walls Can Be Insulated:

After you’ve gotten your tank’s water temperature to an acceptable range for the fish you want to keep, insulating the glass walls is an excellent next step to think about.

This strategy will prevent the heat from escaping, but you may need to conduct warm-water changes regularly. This is the practical disadvantage of not using a heater in an aquarium.

Insulating the glass walls of your tank is a great way to keep the water warm enough for fish. While styrofoam on the back and side panels isn’t very pretty, insulation film or foil will be more accessible on you aesthetically!

6) Get Yourself Some Cold-Water Fish:

Coldwater fish are often sturdy and thrive in cooler water. In addition, they can withstand frequent temperature changes because their body temperatures vary less than those of other types, such as tropical or heated habitats! 

The ideal range for a cold-water species like this would be between 60°F – 68°F (16 – 20 degrees Celsius).

Some of the excellent coldwater aquarium fish are:

  • Sunset Variatus Platy
  • Celestial Pearl Danio
  • Rainbow Shiner
  • Hillstream Loach
  • Endler’s Livebearer
  • Clown Killifish
  • Cherry Shrimp
  • Dojo Loach
  • Goldfish
  • White Cloud Mountain Minnows
  • Paradise Fish
  • Medaka Ricefish

If you’re setting up a tank without a heater, tropical fish are not the perfect choice. They don’t cope well with temperature changes and are susceptible to disease when exposed to unstable water conditions.

Here are some popular tropical fish that require a consistent temperature of 75-80°F in their tank:

Betta Fish, Neon Tetras, Bushy Nose Plecos, Tetras, Cherry Barbs, Swordtails, Dwarf Gouramis.

Case-2: You Have A Heater, But It Is Not Working

When your aquarium heater does not work, the fish are likely to be unhappy. You can prevent this from happening by taking some action before it affects their health.

You Have A Heater But It Is Not Working

1) Check The Heater Status:

Take a look at your fish tank heater and make sure it’s turned on. Then, use an instant-read thermometer to check the temperature of the water.

This is a quick and easy way to test if your aquarium heater malfunctions by taking it out of the tank and placing it in a water-full bucket. If there’s no increase in temperature after 10 minutes or so, you can assume that the heater is out of operation!

You can read – How Do I Know If My Aquarium Heater Is Working

2) Fix The Problem:

If your aquarium heater isn’t working, you can use the instructions below to fix it. 

Re-plug the power cord into the source, ensuring the power outlet does not contact the water. If you’re using a battery-operated aquarium heater, replace the battery. 

If something breaks, don’t try to fix them yourself – take things straight onto the vendor or repairer who will be able to help out more efficiently than an amateur like yourself.

If necessary, purchase a replacement heater for fish tanks.

3) By This Time, Retain The Existing Heat:

When your aquarium heater is unavailable, the best way to keep your fish tank warm is with insulation material like the newspaper. You can also use thick blankets or heavy towels if no newspapers are available.

4) Turn On Lights Of Your Fish Tank:

Aquarium lights can assist you in conserving your fish tank’s heat. Turn on the light and pull the lid over it. Remember that this advice should only be used as a temporary remedy because it can upset your fish in the long run.

5) If Possible, Increase The Room Temperature:

You need temporary solutions to keep your fish tank warm when the heater is out of order. To keep your fish tank at a proper temperature, you can raise the temperature of your room.

You can utilize other heaters (like room heaters, if available.) To see if this helps, experiment with the other heaters in your home. Put the heater as close to the aquarium as possible to maximize the heating impact.

In the winter, each variety of fish will require a particular temperature setting, but for most tropical aquarium fish, the water temperature should be 75°F – 80°F (23°C – 26°C).

In a betta fish tank, the water temperature should be between 76 and 85 degrees Fahrenheit (24°C – 29°C), and the goldfish tank’s water temperature should be between 68 and 74 degrees Fahrenheit (20°C – 23°C).

Case-3: There Is A Power Outage

You’re probably aware that power outages can take many forms and last from a few minutes to hours or even days. The shortest outages usually happen when a power grid is unintentionally or temporarily shut off, your circuit breaker malfunctions, or, in the most simple situation, the aquarium power connection is accidentally unplugged. 

Weather-related or natural-disaster-related outages may take longer to resolve. And a three-hour or more prolonged power outage could be harmful, and the water temperature goes down to affect your fish.

Luckily, you’ve got plenty of ways to keep your fish healthy in the event that power goes out.

There Is A Power Outage

1) Retain The Heat With Insulations: 

The heater will be out of service if there’s a power outage. So, you should try to keep the temperature inside with some insulating materials.

Cover your fish tank with thick blankets, towels, or layers of newspapers to keep the temperature from escaping, but it may not work well enough for long periods!

2) Add Something Hot In The Water:

Warm water can be added to a fish tank, but not directly; it should be turned into a water container.

Boil some water using a gas ring, hiking stove, portable propane camping, or grill (you don’t have electric power, right?). Then Fill a robust plastic container with boiling water, any type that can be sealed tightly.

Ascertain that the container will not melt due to the hot water. To keep the container from leaking water outside, put a drop of dechlorinating fluid inside. After that, you’ll submerge this hot water bottle in the aquarium’s water.

Because the water level in your aquarium will grow as you add more objects to it, you should remove some water before putting them in. After that, add the water container and allow it to float.

If you have a larger fish tank, use one or more floating water packages like this, and when the temperature declines, replace it with a new hot-water container.

3) Keep A Battery-Operated Back Up Heater:

Having a battery-powered aquarium heater on hand in case of a power outage is always a good idea. You can use this type of heater not only as a secondary heater but also as the primary heating unit for your fish tank.

Valuable Add-Ons To Help Keep A Fish Tank Warm Without Heater

With the correct add-ons, you can have a heater-free tank more easily! These are just some items that might work well in your setup and require no additional hardware.

A Lid, Hood, Or Canopy To Cover The Tank

Cover or lid The Fish Tank To Retain Heat

Employing covers will be beneficial if you look for an easy way to keep your fish tank warm without using a heater. Lids trap heat and limit the contact between the water’s surface, and a chilly airflow is a simple step.

Any aquarium lid will trap warmth and make your other warm-up activities far more effective. 

Most tanks can be installed with easily removable tops, allowing you to access the interior of the tank for feedings, maintenance, and aquascaping.

A lid can reduce the oxygen delivery to the water, but you can always add an air pump and an air stone to aid oxygenation.

Intense Lighting

High Light In The Fish Tank To Retain Heat

A similar warm-up effect can be achieved by using a lighting system with stronger lights instead of placing your tank in direct sunlight. This way, you’ll have more control over how much light your unheated tank receives. 

Even without a heater, keeping the lights on for 8-10 hours a day will keep a fish tank warm, especially if we’re talking about a nano aquarium.

Stronger lights and the extra heat they emit will also assist your plants if you’re working on a heater-free planted tank.

In this situation, algae growth may still be a concern, but you can take steps to help with algae control.

Keep The Tank Insulated

Insulate The Fish Tank To keep warm

While some people might see this method as an eyesore, adding insulation film or reflective foil to your aquarium setup is the best way of trapping heat. 

This inexpensive and easily accessible add-on can make a huge difference, especially if you have drafty windows at home or the ambient temperature fluctuates significantly during cold spells!

Thermometers are essential for monitoring the temperature in your tank and giving you an idea of how well (or not!) your heating system work and whether your tank water is at the perfect temperature or not. So you should keep one on hand.


They are your adorable pet which needs more care than the other since it lives in a different environment – water. The temperature change from high to low can sometimes be bad for fish and create problems like an illness!

Whether you want to or need to, there are many effective ways to keep a fish tank warm without using a heater. 

Regardless of which solution you choose, you should invest in an aquarium heater to ensure that everything runs smoothly. 

So now, keep your fish warm, and don’t forget to let me know if you come up with any new ideas or any additional assistance with your fish. 

Sujit Modak

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