How To Keep a Fish Tank Warm Without a Heater: 12 Tips!




How To Keep a Fish Tank Warm Without a Heater

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If your heater has broken, or you’re thinking of starting a fish tank and don’t want to use a heater, don’t worry! There are several ways to keep your fish tank warm without using a heater.

For example, you can keep your fish tank warm by simply placing it in a warm room. If you have a room in your house that tends to be warmer than the others, put your fish tank there. Or just move your fish tank around to different rooms until you find the warmest spot.

In this blog post, I’ll describe how to keep a fish tank warm without a heater so you can decide what will work best for your fish.

How Can I Keep My Fish Tank Warm without a Heater?

Don’t practice heating an aquarium without a heater when you already have an established large tank with tropical fish inhabitants. That’s a recipe for disaster that will result in more fatalities than you can count! These tips are intended to help you get by in an emergency situation.

Use a Smaller Tank

Do you remember learning about how heat transfer works in science class? The smaller the object, the easier it is to heat. The same goes for fish tanks!

If you have a smaller fish tank, it will be much easier to keep it warm without a heater than if you have a large fish tank. This is because there is less water for the heat to dissipate into.

Get Coldwater Fish

Yes, this goes against everything you know about how to keep a fish tank warm. But, if you get coldwater fish, they will be much more tolerant of lower water temperatures.

This is because coldwater fish are used to living in cooler water than tropical fish. So, if the water in your tank is on the cooler side, they will be just fine.

In addition, coldwater fish are some of the hardiest around. They can survive in cooler water temperatures and are much more resilient to changes in temperature. This makes them ideal for tanks with temperatures between 60-74°F (20-23°C).

Turn up the Heater in Your House

We often get attached to the temperature in our homes and don’t want to budge from it, but if you have a fish tank, it’s worth considering turning up the heat a bit.

If your aquarium is in a room that’s about 78 degrees Fahrenheit (25.5 Celsius), that change might be enough for some nano tanks with coldwater fish.

Bring Your Aquarium Closer to a Source of Heat

No home is perfectly heated – there are always colder and warmer spots. If you don’t have a heater for your aquarium, take advantage of this by setting it up in a warmer place. This way, you’ll save yourself the extra hassle (and expense) of heating the water.

Below are the guidelines for finding the best place to put your tank:

  • A higher level (in a multistory house): Moving your aquarium to a higher level in your home can change the temperature by at least a couple of degrees. Upper levels are often much warmer than lower levels.
  • No drafty spots: If your home has poor insulation, it can make keeping your fish tank at a consistent temperature difficult, no matter how good your central heating system is.
  • Sunnyside is best: Place your nano tank in an area of your home that gets at least six hours of sunlight per day, and you’ll be amazed how quickly it will warm up without any extra effort.

Note: If you opt for the sun-heated method, keep some algae solutions on standby. When sunlight is abundant, it causes algae growth to surge.

Use Warm Water for Water Changes

If you want to maintain a specific water temperature in your tank without using a heater, do frequent water changes using slightly warmer water.

Of course, you’ll have to raise the temperature slowly – no more than 1° per hour. Raising it quicker than that can be harmful to some fish species.

If you opt to use this method of heating your fish tank, remember that you will need to set aside extra water for the required changes. You can mix room-temperature water with boiling water but never add it directly to your tank (even if it’s empty!).

Insulate the Glass Walls of Your Tank

After adjusting the water temperature in your fish tank to a habitable level for your desired fish, insulating the glass walls can be helpful.

While covering the back and side panels of the tank with styrofoam isn’t pretty, utilizing insulation film or foil accomplishes the same goal effectively.

This method will help to keep the existing warmth from escaping, but you may need to continue doing warm-water changes. This is the drawback of not having a heater in an aquarium!

Raise the Temperature of Your Tank’s Water Gradually (Temporary Solution)

Similar to warm water changes, this method is delicate but can be helpful when trying to maintain a fish tank’s temperature without using a heater.

You can increase the water temperature in your tank by slowly adding a sealed bottle of hot water to your aquarium and letting it float. For example, if you’re trying to heat the fish tank temperature to 80°F, the water inside the floating container should be 120°F.

This option might not be the most efficient, but it’s still available if you must go heater-free. However, please note that doing this may cause large swings in water temperature.

So, if you have sensitive fish, it’s probably best to avoid this method and opt for something that will create more gradual temperature changes.

Put a Lid, Hood, or Canopy Over the Tank

Covering your fish tank limits the amount of contact between the water’s surface and colder air, thus keeping the water warm without a heater.

Most tanks can be fitted with easily removable tops, so you still have access to the interior for feedings, maintenance, and aquascaping.

However, adding a lid may cut the oxygen levels in your tank if it’s not properly ventilated. So, make sure you have an air stone or other aeration device running if you go this route.

Use Stronger Lights

If you want to replicate the effect of placing your aquarium in direct sunlight without actually doing it, use a lighting system with stronger aquarium lights.

This way, you can maintain better control over how much light exposure your unheated aquarium gets, which can help prevent algae growth.

Keeping the lights on in your aquarium for eight to ten hours per day will create enough heat to warm the water without a heater, especially if it’s a nano aquarium. If you have plants in your aquarium, they will also benefit from stronger light because it generates more heat.

Use an Energy-Inefficient Filter

If you don’t have a heater for your fish tank, one of the most out-of-the-box solutions is to use an inefficient filter. Less efficient filters tend to generate more heat because they use so much extra energy.

Simply put, the filter’s motor can quickly raise the temperature of the water in the tank quite a bit. Pair this up with an insulating material, and you’ve got a pretty good system for heating a fish tank without a heater!

Use a Heating Mat (Only for Small Fishbowls)

While heating mats are primarily used for terrariums or vivariums, they can be employed to raise the water temperature in a small fishbowl. The main drawback is that you’d have to put a barrier between the heating mat and the bottom of the bowl to stop hot spots and glass cracking.

Since glass isn’t great at conducting heat, this would be one of the least efficient methods. This warming-up method is more experimental than some of the others previously mentioned.

In an Emergency, Bring Blankets or Thick Towels

If you’re looking for a long-term way to keep your fish tank warm without using a heater, this isn’t the right solution. However, if you need an emergency measure, insulating with a thick blanket will be your best bet.

If there is a power outage, wrapping a blanket or thick towel around the tank’s glass panels will help stabilize the temperature and make it take longer to cool down. Sudden temperature drops can kill fish, especially those that are not tolerant of cooler water.

Why Might I Need to Keep a Fish Tank Warm Without a Heater?

Not sure why keeping a fish tank warm without using a heater would appeal to anyone? There are several reasons an aquarist might want (or have to!) undertake this:

  • Power outages: If there is a power outage, you obviously won’t be able to use a heater to keep your fish tank warm. Insulating with blankets or towels can help to prevent drastic temperature changes that could kill your fish.
  • Heater malfunctions/replacements: If your heater breaks or you can’t afford a replacement right away, then keeping the tank warm without one will be your only option.
  • Housing tropical fish: Some tropical fish can’t tolerate cooler water temperatures, so you’ll need to take measures to keep the tank warm even if you’re not using a heater.
  • Setting up a quarantine tank: When setting up a quarantine tank, you want to avoid adding anything unnecessary that could contaminate the water. This means not adding a heater if it’s not absolutely necessary.
  • Extreme temperatures in winter: If you live in an area with very cold winters, keeping the tank warm without a heater will help prevent the water from freezing and damaging the tank.
  • Going for a cordless system: If you’re looking for a way to heat your tank without having cords running everywhere, then an inefficient filter or heating mat could be the solution!

How To Keep My Fish Tank Warm Without a Heater in an Emergency?

How To Keep a Fish Tank Warm Without a Heater

If your fish tank heater breaks and you’re in an emergency situation, use these tips to keep your tank warm:

  • Ensure that your fail-safe measures are active, such as pre-installed backflow tubing and sump shut-offs.
  • To insulate the filtration system, use blankets, thick towels, or cardboard to wrap it.
  • Make sure to cover the glass panels and the top of the tank to keep heat from escaping.
  • Ensure that your fish have enough oxygen by not blocking the entire tank’s supply.
  • Only remove the temporary insulation layers when absolutely necessary – every time you do, heat will escape and make it harder to keep the fish alive.
  • Use a sticker thermometer to monitor the water temperature. Although it may not be the most accurate, it will notify you if the temperature drops too low for the fish inside, which could threaten their health.
  • Take action to start warming up the tank now, without a heater. If worst comes to worst and your emergency drags on, you’ll need to slowly warm up the tank using the above methods so it doesn’t reach a dangerously low temperature.

What Is the Ideal Water Temperature in a Fish Tank?

Most fish feel comfortable at temperatures between 76 and 80 degrees Fahrenheit, making this setting ideal for most aquarium dwellers.

If the water temperature exceeds 80 degrees or falls below 76, it could be detrimental to fish health. However, there are some instances where such conditions are beneficial for specific species.

How Do Extreme Temperature Changes Impact Fish?

Fish cannot acclimate to sudden or large temperature changes as easily as we can. They are much more susceptible to thermal stress, which impairs their immune systems and makes them more susceptible to disease and infection.

In severe cases, sudden temperature changes can even kill fish. This is because their internal organs are not as efficient at regulating their body temperature as ours are.

When fish experience thermal stress, you may notice them gasping for air at the water’s surface or hiding more than usual. If you see these signs, it’s important to take action to stabilize the water temperature as soon as possible.

Can Fish Survive in Extremely Hot or Cold Water?

There are a few creatures that can manage hot water for a short time. For example, some types of fish in Death Valley can endure temperatures up to 113°F. Also, some tilapia fish swim in springs with even hotter water.

Even though these animals can stand the heat for a little while, they eventually start to die because the protein in their blood starts to coagulate.

However, some fish can live in colder climates due to an antifreeze-like substance present in their blood. For instance, plenty of fish dwell near the Arctic and Antarctic Circles.

Which Fish Are Most Affected by Water Temperature Changes?

Tropical fish are a big no-no if you’re setting up a tank without a heater. They don’t do well with temperature fluctuations and are prone to diseases when stressed from inconsistent water conditions.

The following fish thrive in tropical environments where the water temperature is kept consistent at 75-80 degrees Fahrenheit:

  • Neon tetras
  • Guppies
  • Bushy nose
  • Plecos
  • Congo tetras
  • Cherry barbs
  • Swordtails
  • Dwarf gouramis
  • Panda cory cat
  • Betta fish

Furthermore, corals require UV lights and appropriate water conditions with a steady temperature to prosper and stay alive. Maintaining the correct water temperature for this type of aquarium (between 75-78°F) is difficult to do without a heater in a minimalist system.

Which Fish Types Can Withstand Water Temperature Changes?

Coldwater fish won’t be affected by not having a heater in their tank for extended periods! These fish species can live in diverse water temperatures and survive big temperature changes.

The following fish are hardy and can prosper in water temperatures between 60-74°F (20-23°C):

Coldwater fishWater temperature range
Comet goldfish60-70°F
White cloud minnows64-72°F
Paradise fish60-86°F
Variable platyfish61-75°F
Rainbow shiners60-80°F
Hillstream loaches68-75°F
Endler's livebearers64-84°F
Clown killifish68-79°F
Cherry shrimp57-84°F
Dojo loaches68-76°F


How Long Can a Fish Go without a Heated Fish Tank?

Depending on the type of fish and where you live, you may or may not need a heater. For example, if you own a betta fish and live in an area with a tropical climate and a year-round temperature of 80°F, then you likely won’t need a heater for your fish tank for at least a couple of years.

Is the Size of My Aquarium Heater Important?

It’s important to consider an aquarium heater when starting up your tank. You’ll need to figure out the wattage per gallon requirement and find a size of heater that will work for your specific needs.

Aqueon is a highly-regarded manufacturer of aquariums, lighting, heaters, and other fish-keeping-related products. According to their experts, Aqueon suggests that a good rule of thumb to work out the size of the aquarium heater you need is to allow 5 watts per gallon for 55-gallon tanks and less. Allow 3 watts per gallon for tanks over 60 gallons.

If your tank is in a particularly cold room or is positioned close to an exterior door or on an outside wall, you might need to use a larger size heater or even a second unit.

Heater Guidelines

The guidelines shown in the table below are based on a standard room temperature of 68°F to 72°F Fahrenheit.

To Increase °F Above Room Temperature
Aquarium Size5°F10°F15°F
5 gallon50 watt50 watt50 watt
10 gallon50 watt50 watt100 watt
20 gallon50 watt100 watt100 watt
30 gallon100 watt100 watt150 watt
55 gallon150 watt150 watt200 watt
75 gallon200 watt200 watt300 watt
90 gallon300 watt300 watt300 watt


How Do Aquarium Heaters Function?

The purpose of a fish tank heater is to generate heat and maintain a specific water temperature in your aquarium.

The aquarium heater can do this automatically, turning on when the water needs heating and then turning off once the desired temperature has been reached.

Last Words

Phew! That was a lot of information on how to keep your fish tank warm without a heater. As you can see, each method has pros and cons, so it’s important that you weigh the options and decide what’s best for your fishy friends.

Do you have any experience with keeping fish tanks warm without heaters? We’d love to hear about it in the comments below!

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