Guideline: How To Keep A Fish Tank Warm Without A Heater

These following ‘how to keep a fish tank warm without a heater’ will save your day when the power goes out, you break your aquarium heater, or you don’t even prepare a heater for your fish tank.

On cold days, your tropical fish, your bettas, etc. will need a warmer environment to keep their lives stable. And that is when an aquarium heater becomes more significant than ever. But who knows whether the electricity encounters a problem or you must prepare a backup heater for your fish tank?

Now, let the tips below that show how to keep a fish tank warm without a heater help you and your fish.


How To Keep A Fish Tank Warm Without A Heater

#1: Your heater is out of service

You will need:

  • A thermometer and a bucket of water
  • Newspaper, thick towel or blanket
  • Other types of heaters in your house

Don’t forget to use a thermometer to check the fish tank temperature frequently

Step 1: Check the heater status


Check the light and the place of aquarium heater to see if it still work properly

  • Take a look to see if the light of your fish tank heater is on
  • Use a thermometer to check the fish tank temperature
  • Test if the heater has a malfunction by turning it on while placing in a bucket of water and check the temperature
  • Follow the ‘How to tell if an aquarium heater is broken’ detailed steps to define the heater status exactly

Step 2: Fix the problem if the heater is not truly broken

  • After testing, if it still working properly in the bucket, try following the ‘where to place aquarium heater instruction’ to put the heater on the right place, and in the right way.
  • Re-plug the power cord in the source, make sure you keep the power outlet from touching the water
  • Change the battery if you are using a battery powered aquarium heater
  • If it broke, don’t try to fix it yourself, bring it to the seller or the repairer, and get a new heater for fish tanks if needed
  • Move to next step

Step 3: Retain the existing heat


You can use aquarium lights to keep the fish tank warm without a heater

  • Paper is an insulation material, so you can cover your tank with multi-layer of newspaper to keep the heat from escaping the tank
  • In case you don’t have enough newspaper at the time, a thick blanket or some heavy towels can help
  • An aquarium light can help you to save the heat of your fish tank: Turn on the light and do not cover its hood (or it will be easier to catch fire). Remember that you should only use this tip as a temporary solution since it can help but also bother your fish at the same time.

Step 4: Using other types of heaters to generate the fish tank temperature

  • How lucky is that you still have the power. Try turning other heaters in your house
  • Put the heater next to the aquarium to push the heating effect
  • You can also raise the temperature of your room to keep the fish tank warmer in a proper heat level, especially in winter

Turn on the heater in your house to help maintaining the fish tank temperature

In many houses, there aren’t any heater available, but don’t worry because these above tips are how to keep a fish tank warm in a cold room, when the heater broke in tropical fish tank, betta fish tank or any other types that need warm water. If you are wondering about ‘How can I heat up my fish tank faster?’, the answer is combining the third and fourth step.

Read more:  Do Goldfish Need A Heater? Goldfish Temperature Guide

After all, you should get a small aquarium heater or large aquarium heater (depends on the aquarium heater wattage per gallon) as soon as possible to maintain cold water fish tanks in the right temperature easily.

#2: There is a power outage

You will need:

  • A thermometer
  • Newspaper, thick towel or blanket
  • Candle, jar and tin foil for an emergency heater (best in 8”x2” size)
  • Materials for floating water container

In this case, no matter if your small fish tank heater is broken or not, you can’t use it. Therefore, you can take these solutions to save your fish.

Step 1: Retain the heat in your fish tank

Try to cover your fish tank with thick blankets, towels, or lots of newspapers layers to keep the temperature from escaping.


Using newspaper cover around your fish tank to keep the existing heat

Step 2: Make some water containers

We might ask, “Can I add warm water to a fish tank?” when there is no aquarium heater available. Yes, you can add warm water to a fish tank but not in a direct way, you should turn it into a water container.

  • Boil some water with gas, charcoal, or wood, using a gas-ring, hiking stove, portable propane camping or grill
  • Pour the boiled water into a sturdy plastic container, any types that can be sealed tightly
  • Make sure it will not melt because of the hot water. You should add a drop of dechlorinating fluid inside the container to prevent it from leaking water outside
  • Use one or more floating water packages like this if you have a larger fish tank
  • The water level will rise, so you should take out some water in the tank before putting them in. Then place the water container in and let it float
  • You can pour the aquarium water onto the container to make circulation and add more oxygen manually at the same time
  • Refill or replace a new one when the temperature starts dropping down

Step 3: Make an emergency heater for power outage

  • Melt the candle wax by a bain-marie way
  • Put the sand into a vertical jar (up to one third or a little bit more of the jar’s height)
  • Add a wick above the sand
  • Pour the melted wax into the jar
  • Wait for the wax to cool down and turn into hard
  • Put it in the tank to raise the heat up
  • You can use a tin foil to cover the aquarium surface, make a hole that fit the emergency heater to protect the fire as well as keep the tank warmer
  • Make an extender is an effective way to support the emergency heater in a higher tank. You can add in a PVC coupler below the heater, stick it with some double-sided tapes to help it float better. Add some more below to get the needed height.

Candle in a jar that keep floating in the tank can be used as an emergency heater

If you want to find out how to heat up fish tank water quickly or how to heat a fish tank without power, choose either solution in the second step or third step or both along with retaining the heat to create a suitable environment for your fish.

#3: You don’t have any heater

  • Prevent heat from escaping with some cover
  • Turn up the heater inside your house
  • Make some water container or emergency heater to help
  • Or just let it be if the temperature in the place you live is suitable for the fish

Actually Need An Aquarium Heater

Do I need a heater for my betta? do I actually need an aquarium heater? some people will advise you to get a room heater than an aquarium heater. Since if your house is in more proper temperature, it doesn’t need to buy a fish tank heater. With that way, you can save more power, stay away from some problems happening when you broke a heater.

In general, you might not need a heater for your fish tank when your living condition even needs a cooler, and your fish is a kind of non-tropical fish. But for all other situations, an aquarium heater is highly necessary for your fish.

It could be a disaster if the temperature in your fish tank drops down suddenly. All the tips above can help you keep a fish tank warm without a heater, but that means you will have to heat the tank manually, while the aquarium heater control and maintain the suitable temperature for your fish automatically. You only need the best aquarium thermometer along with the best fish tank heater to get the best heating result.

Besides, an aquarium heater is a must-have in winter, because your aquarium temperature control should be between 20 to 28 Celsius degrees to make the best living conditions for your fish.

Do bettas need a heater?

Yes, it absolutely needed. Betta fish are really sensitive to their living environment. The fish tank water that is either too cold or too hot can also cause some health problems for the fish. Therefore, it needs a betta fish heater to properly maintain the betta fish temperature in your tank for keeping bettas warm in winter, and staying in good health as well.


Betta fish do need a heater for their life

Frequently Asked Question about Heater

How do aquarium heaters work

A fish tank heater will turn electricity into heat and maintain the preset temperature for the water in your aquarium tank.

The aquarium heater can turn on automatically to heat the water, then also turn off automatically when the temperature meets the need.

Is the aquarium heater size matter

Yes, it does matter. Define an aquarium heater size that is matched with your tank is actually find out the aquarium heater wattage per gallon.

You can choose an aquarium heater based on the tank size and the temperature needed.

For example, if you need to heat 18 degrees Fahrenheit more for a 20 gallons water tank, you must use a 75W heater to offer enough power that can reach the goal.

Following this table to get the most suitable aquarium heater for your fish tank.

Tank Size


5°C - 9°F

10°C - 18°F

15°C - 27°F

5 gal

25 watt

50 watt

75 watt

10 gal

50 watt

75 watt

75 watt

20 gal

50 watt

75 watt

150 watt

25 gal

75 watt

100 watt

200 watt

40 gal

100 watt

150 watt

300 watt

50 gal

150 watt

200 watt

2 x 200 watt

65 gal

200 watt

250 watt

2 x 250 watt

75 gal

250 watt

300 watt

2 x 300 watt

Which are the best aquarium heaters

Among many brands of aquarium heaters in the market, these could be considered as the best options for you:

  • Aqueon submersible aquarium heaters: It’s shatterproof and has lights with different colors to let you know the heater’s working status easily
  • Marina aquarium heater: Effortless for you to use the heater and set up into the fish tank
  • Tetra HT submersible aquarium heater: This small fish tank heater is affordable for many people, has enough essential functions, and you can put it in whatever place you want
  • Top Fin aquarium heaters: Top fin aquarium heaters can show the exact temperature, along with a special design to help it distribute the heat more evenly in your fish tank
Read more:  How To Tell if Aquarium Heater is Broken? These Things Can Help!

How can I keep my betta fish water warm

You can set a heater in the betta fish tank while the fish still be inside the tank, just make sure you touch the fish. If it is hard for you to do so, (due to the small tank or other reasons), gently bring the fish out of the tank, let them stay in a bucket of water and put them back as soon as you finish setting the heater up.

The aquarium temperature control for betta fish should be around 76-85 degrees Fahrenheit or 24-29 degrees Celsius in winter or maintain 25-27 degrees Celsius in normal condition. 

What is the best temperature for heater in winter


Find out the most suitable temperature for your types of fish is a must

Each type of fish will need a different temperature preset in winter, like:

  • Water temperature in the betta fish tank should be between 76 and 85 degrees Fahrenheit or 24 and 29 degrees Celsius
  • Water temperature in the tropical fish tank should be between 75 and 80 degrees Fahrenheit or 23 and 26 degrees Celsius
  • Water temperature in the goldfish tank should be between 68 and 74 degrees Fahrenheit or 20 and 23 degrees Celsius

In general, you can maintain the heat of your fish tank around 75 - 80 degrees Fahrenheit for the best environment.


Fish are your adorable pet which needs more care than the other since it lives in a different environment - the water. The water temperature can change easily from high to low that may create some bad effects on your fish. This is the reason why maintaining the fish tank temperature is a big factor that every fish owners should care about.

In many cases, like those that have been recommended earlier in this post, you might encounter some problems like a power cut, or your heater has a malfunction, or your didn’t live with a heater before. These situations mean that you will need to heat the tank up on your own, by hands. I hope I have provided enough answers for how to keep a fish tank warm without a heater that you can choose and easily turn these into actions.

Regardless of which ways you choose as a solution, you should get an aquarium heater to keep the work performing in its best way. Now, keep your fish warm and don’t forget to share with us if you have some better solutions or need more help with your fish. We will support you as soon as we receive your requirement.

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