Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (2023)

Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (1)

If you want a compact aquarium, carefully consider the size of the equipment.

Which small aquarium heater fits best and heats the water in a small tank?

Even the water in a 3 gallon miniature tank would need to be heated, especially if you have tropical species like betta fish.


  1. The best aquarium heaters that are small - reviews
  2. How to choose a good aquarium heater

Whether your tank holds 10 gallons or 5 gallons of water, it's important that you maintain a stable temperature.

With that in mind, I'm going to walk you through the smallest aquarium heaters.

Top small aquarium heater

heater brand:For aquariums:longest dimension:
1. Tauchheizador Hygger2.5 to 6.5 gallon tanks4.5 inches
2. Aqueon preset aquarium heaterbest for small 3, 5, and 10 gallon tanks5.75 inches
3. Kobalt Aquatics Adjustable Heater2, 2.5, 3, 5 and 10 gallon aquariums6.5 inches
4. FREESEA Mini Aquarium Heater with Temperature Indicatorbest for 3 to 10 gallon tanks3.7 inches
5. Aqueon Mini Heaterbest for small tanks with 1, 2, 2.5 gallons of water3.1 inch smaller heater

In my reviews, I was careful to only list heaters that are less than 6.5 inches long and suitable for small aquariums.

I also made sure to follow the safe rule of havingat least 5 watts of heat output per gallon of water.

But before we continue, it is worth mentioning that the idea of ​​​​installing a heater in aquariums smaller than 3 liters is unfeasible.

The space is already narrow enough andVery few fish can be kept in such a small tank., despite what pet stores advertise as betta fish.

Anyway, if you want shrimp in a small heated tank with 2 gallons of water or less, you can get the Aqueon Mini 5W. With dimensions of 1.13 x 0.88 x 3.12 inches, that is,Aquaon Mini 5Wit is the smallest aquarium heater that is reasonably reliable for tanks this size.
Here are the best small aquarium heaters that are perfect for nano aquariums:

1.Hygger immersion heater with digital display

Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (2)
Click here for current pricing + MORE photos on Amazon.

The Hygger Submersible Aquarium Heater is a compact, oval-shaped heater that fits tanks between 2.5 and 6.5 gallons.

The heater itself is slightly larger than the pictures, with its longest dimension being 4.5 inches.

Manufacturers recommend using this heater in tanks from 1 to 6.5 gallons, but I think it would run a little big on tanks smaller than 2.5 gallons.

I also think this 50W heater would be powerful enough to self-heat a 10 gallon tank, but I haven't personally tested it.

Also,3 gallon tanks are the minimum for a betta fish, keep this in mind when purchasing the Hygger heater for your new Betta aquarium.

Regardless, the Hygger immersion heater does its job well and keeps the water hot in my little 5-gallon tank.

It heats up quickly, but not too quickly to stress my fish.

Another thing I like about the Hygger heater is that it has its own protection to stop working if it's not completely submerged in water.

That kind of security protection is a rarity at this price point, so kudos to the brand for that.

Regardless, I'm pleased with the overall design of this aquarium heater:

  • The protective plastic cage gives it a cool look;
  • The temperature controller is outside the tank on the wire, which is very useful;
  • The suction cups work reliably and haven't moved since I adjusted them.

The only downside I would mention is that the heater's internal thermometer can sometimes be more than 1 degree F off.

Author's note:I recommend that you always use a separate dedicated thermometer in your aquarium. It doesn't matter if your heater measures the water temperature or not. This is the kind of best practice you shouldn't ignore.

Either way, the Hygger Submersible Aquarium Heater is a great addition to small tanks in the 2.5 to 6.5 gallon volume range. I wouldn't hesitate to buy one if I needed something compact and affordable.


  • 4.5 inches long
  • attractive price
  • When the preset temperature is reached, it will stop heating and wait
  • Automatic shutdown when heater is below water level
  • It also automatically shuts off if the temperature is above 95 (according to its own built-in thermometer)


  • No Warranty
  • Sometimes the LED reading can differ by more than 1 degree (but you should still use a separate thermometer with each heater -hereis a good option)

2.Aqueon preset aquarium heater

Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (3)
Click here for current pricing + MORE photos on Amazon.

The Aqueon Preset Aquarium Heater was one of the first heaters I came across when looking for something to warm up.My betta fish's 5 gallon aquarium.

The 50 watt version of this heater is suitable for small tanks such as 3 gallon, 5 gallon and 10 gallon tanks.

The Aqueon Preset Aquarium Heater comes with a preset thermostat set to a temperature of 78°F.

Manufacturers claim that the expected deviation from the set temperature is only 1 degree. However, this depends on the size of the tank and the temperature in the room.

I recommend you buy onesmall aquarium thermometerto check if the water temperature differs from the default Aqueon heating setting.
Regardless, this preset aquarium heater is relatively small, with a 50-watt heater measuring just 5.75 inches long.

A standard 5 gallon aquarium is 10 inches (25.4 cm) tall.

This means that if you have a black background in your small aquarium, the Aqueon Aquarium Heater will fit right in and be almost invisible.

Its understated appearance really doesn't bother aquarium inhabitants or their eyes.

Another advantage of this small heater is the cheap price.

After all, this is a preset device with no customization extras.

This makes the Aqueon preset aquarium heater a "set it and forget it" solution.

One thing to note about this compact water heater is that it should only work when fully submerged.

You can phrase it however you like, as long as this condition is met.

Choosing horizontal or vertical placement depends on personal preference and how you want your nano tank to look.

Another advantage of the Aqueon small heater is that it comes with a 12 month warranty.

That's a good thing because it means manufacturers are confident in its construction, despite it being a fairly inexpensive piece of technology.

However, as this is a preset heater, in some cases the Aqueon's red indicator light may not turn off if the ambient temperature is too low.

This usually means that the aquarium is too big for the small heater you have, or that the unit has a manufacturing problem.

When I had this problem, I just ordered a low wattage heater for my setup, as I was initially testing the 50 watt version on a 30 gallon tank.

The Aqueon 50 Watt Preset Heater works best with 3 gallon, 5 gallon and even 10 gallon tanks.


  • 1 year warranty
  • Only 5.4 inches long for the 50-watt version
  • set it and forget it
  • Automatic shutdown when preset temperature is reached
  • Very good price for what you get in terms of quality.
  • material inastilável
  • You can place it horizontally or vertically in your small tank.


  • Not adjustable (still the default water temperature is 78 degrees Fahrenheit, which works in most tropical freshwater aquariums)
  • There is no indication of the current temperature in the tank (you can get a small aquarium thermometer for under $2here)

3.Cobalt Aquatics Adjustable Aquarium Heater with Thermostat Controller

Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (4)

Click here to compare prices + see MORE photos of this product:

The small Cobalt Aquatics water heater is a bit more expensive compared to other nano aquarium heaters.

However, there's a solid reason for its price.

First of all, this aquarium heater has a fresh look.

Secondly, the material it is made of is an unbreakable thermoplastic and its discreet design allows the heater to easily fit into any aquarium.

The 25 watt Cobalt Aquatics Neo-Therm heater is suitable for both 2.5 gallon and 3 gallon aquariums, while the 50 watt version will work best in water in a 5 gallon and 10 gallon heated aquarium.

A quick note: most 3-gallon aquariums are over 9 inches tall, but it's a vertical space with no substrate.

Make sure the Neo-Therm Aquarium Heater's 6.5 inches are submerged in water when using it in a 3 gallon tank, as this heater doesn't seem to be able to be placed horizontally.

A big advantage of the Cobalt Aquatics Small Heater is that it has an adjustable thermostat.

A controllable aquarium heater that is also small enough to fit in a nano tank is a rare find.

This tiny heater's built-in thermostat senses the temperature of the aquarium and responds to maintain the desired water temperature.

Unlike my previous choice, this aquarium heater has its own adjustable temperature controller, giving you flexibility in selecting fish and invertebrates for your small aquarium.

Anyway, the best thing about this compact water heater is that it comes with a 3 year warranty.

That's the incredible guarantee for every aquarium heater (in general).

Working with the Cobalt heater is very easy because you can see the set temperature and the actual water temperature at the same time.

If you want to be sure the desired heat is being achieved, simply look at the green indicator light located on the heater's temperature controller.

If it does not flash, it means that the temperature has already been reached.

Talking about the operation of this aquarium heater, there may be a small snag in the process.

If you want to adjust the water temperature in the aquarium, keep the button pressed and wait a few seconds until the green light on the screen completely surrounds the button.

Another thing I haven't personally experienced, but some people report, is that cupping doesn't always last longer than a few months.

I was able to adjust the suction cups on my small Cobalt Aquatics aquarium heater the first time around and it has been stable ever since.

Still, compared to everything this little aquarium heater does for your aquarium, I'd say those are minor concerns.

In my opinion, the overall performance of this compact aquarium heater is really good and if you finally choose it, you will probably be more than satisfied.


  • 3 Year Limited Warranty (Yes!)
  • adjustable temperature controller
  • reliable thermostat
  • Accurate temperature measurements with very little deviation
  • It has automatic overheating protection.
  • breakable thermoplastics
  • elegant design


  • More expensive compared to other smaller aquarium heaters on the market.
  • Some reports say that this particular type of aquarium heater rarely fails due to malfunction, but because of the 3-year warranty, you won't have to wait long for a replacement.

4.FREESEA Mini Aquarium Heater with LED Temperature Display

Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (5)
Click here for current pricing + MORE photos on Amazon.

Although I only used it for my 10 gallon tank for a few months, I loved this nano water heater.

The first thing you'll notice about the FreeSea Mini Aquarium Heater is its shape.

Like Hygger's aquarium heater, this one is quite small and... round.

Yes, it's an interesting shape and I'm really surprised at how elegant it looks.

The largest dimension of this small heater is only 3.7 inches, making it perfect for even the smallest nano tanks.

It comes with a 1 year warranty and a super practical LED display that constantly shows the temperature of the water in the aquarium.

In fact, the red digits are big enough to be seen from afar.

Another interesting feature of this small aquarium heater is that it switches itself off once the set temperature is reached.

It might not sound like much, but considering the price of this product, it's more or less surprising.

Just remember that the Freesea Small Heater is fully submersible and should never be operated out of water (like all aquarium heaters listed here).

Either way, it's just the temperature knob that sticks out of the water, which is pretty handy considering you don't have to dip your hands in the tank to set the water temperature.

The FREESEA Mini Aquarium Heater also has its downsides, but they aren't too bad.

For example, I've found that the unit won't stop heating after the water evaporates and the heater isn't surface covered, which can lead to potential electrical issues.

This is where the Hygger heater trumps the FREESEA. The Hygger One stops when it runs out of water.

Because of this, you should keep an eye not only on the LED display, but also on the water level.

Another small downside for me is the short cable.

You may need to place the tank somewhere near an exit.

However, despite its compact size, this aquarium heater may not be a good fit for really small tanks like the 2 gallon tank as it can be overwhelming for such a volume of water.

Use the 50 watt version in 3 gallon, 5 gallon and 10 gallon aquariums only.


  • 1 year warranty
  • Small, oval in shape, only 3.7 inches long, suitable for even the smallest aquariums.
  • Accurate temperature readings on the LED temperature display
  • The thermostat is reliable and the maintained water temperature shows only minor deviations
  • Adjustable
  • The temperature controller is out of the water, so there's no need to dip your hands in the aquarium to make adjustments.
  • elegant look


  • short cable
  • Won't come off unless covered with water

5.Aqueon Mini-Aquarienheizer 5W- the smallest.

Top 5 Small Aquarium Heaters (less than 6.5 inches) for Nano Tanks (6)

Click here to see MORE photos of this product on Chewy.

The Aqueon Mini Aquarium Heater comes in a small and compact size with a length of 3.1 inches.

These dimensions make the Aqueon Mini Heater the smallest aquarium heater you can get for your nano aquarium.

This extremely small aquarium heater comes with a 90 day warranty.

Doesn't sound like a long enough warranty period, but given its size and performance, it's understandable.

Of course, this water heater should only be used in temporary aquariums that would otherwise be too small to house tropical fish for a long time...

That said, if you have a new Betta in a small tank that is about to be upgraded, the Aqueon Mini Heater is for you.

In my experience, the 5 watt version works best for aquariums and fish tanks that hold between 1 and 2.5 gallons of water.

It is also possible to raise the water temperature in a 3 gallon tank with the 5 watt mini heater, but it will take time and maintaining the temperature may not be realistic at night when the room gets cold.

Anyway, using this super small heater is as easy as it gets.

It's a preset, which means just turn it on and go.

Just get a thermometer to see if the heater can raise the temperature of your little tank.

For the sake of transparency: I personally did not use this heater, but one of my friends who grew Artemia as live food for his fish did.

What made him not happy about using the mini aquarium heater was the fact that there was no indicator light to tell whether the heater was on or off.

So if you have this heater in your small tank, you'll need to occasionally check the water temperature to make sure it's in the desired range.

The last thing you need to know about this super small aquarium heater is that it is fully submersible and you can place it either horizontally or vertically.

Overall, the 5 watt version of the Aqueon Mini Aquarium Heater is a great solution for heating water in a 1 to 2.5 gallon tank.


  • The smallest heater you can get for your aquarium at just 3.1 inches long
  • 3 month warranty
  • Works in very small tanks (1, 1.5, 2, 2.5 gallon aquariums)
  • economic
  • material inastilável
  • easy to use


  • No light indicates whether the heater is on or off
  • It's not a long-term solution and will likely need to be replaced immediately after the warranty (still a great option if you need a cheap fix temporarily).

A to Z Guide to Choosing a Heater for a Small Aquarium

While purchasing an aquarium heater for your pet's home can seem daunting, it doesn't have to be.

There are some factors to consider before making your final decision.

With that said, here are some things worth considering before purchasing a small aquarium water heater:

With or without thermostat?

Before purchasing an aquarium heater, you should consider whether you want it with or without a thermostat.

If you look at some products online, you will see that not many manufacturers offer small aquarium heaters without a built-in thermostat.

The reason for this is the general agreement on the overall safety of the aquarium.

The thermostat communicates with the heater that when the temperature of the water in the tank reaches the desired level, it is time to turn it off.

A thermostat is essentially just that: a device that takes measurements based on the temperature of a medium (in this case, the medium is water).

It is very important that your small aquarium heater has a thermostat, as this will prevent the creatures inside from being boiled alive.

The heater should be durable but have realistic expectations.

We all want to buy an aquarium heater and stick with it until the end of our little trip to the aquarium.

Unfortunately, this is more of a utopia, because nothing lasts forever.

Let's face it, electronics fail, break and don't work properly.

However, that doesn't mean there aren't long-lasting aquarium heaters.

The best indicator of a heater's durability is the warranty period.

The warranty period reflects the manufacturer's confidence in its product.

The longer the warranty, the more likely your small space heater will last longer.

On the other hand, it is naive to expect an aquarium heater to last several years.

If your aquarium heater is at the end of its warranty period, it would probably be a smart move to replace it with a new one.

Get an extra heater just in case.

It's always a good idea to have a little backup plan in case your aquarium's main heater stops working for whatever reason.

You can get another one just to be sure.

At best, you'll need it in a few years, so why not buy two and avoid some problems down the road?

Speaking of quantity, there is another reason why you should buy two aquarium heaters.

I've discovered a little trick over the years that seems to work for other people as well.

If you are worried that your beloved fish will one day freeze or fall prey to a parasite outbreak, buy two heaters of the same type.

Make sure both are at the recommended power for your aquarium size.

Place both in the tank and set them to the same water temperature.

That way, if one heater fails, the other will see the drop in water temperature and make up for the loss.

In this way, you make your aquarium TWICE more resistant to temperature fluctuations that occur at night or on rainy summer days.

Fluctuations in water temperature are often the reason for disease outbreaks in fish.

This usually works for larger tanks and may not be practical on small tanks holding less than 3 gallons of water.

Temperature controls are nice, but you might not need them.

If you decide to use a preset heater, you already know that you cannot regulate the temperature in the aquarium.

These heaters undoubtedly have their advantages, the main ones being time savings in adjusting the degrees and also an extremely affordable price.

But they don't offer much flexibility as to the type of fish or invertebrate species you can keep in your small tank.

If it's a single species nanotank, like a 5 gallon betta fish tank, it makes sense to use a preset heater.

However, if you plan on experimenting with different types of nanofish, you should probably get an aquarium heater with a temperature controller.

Get the most powerful heater when your home's average room temperature is low

Manufacturer recommendations for an aquarium heater are relative.

If it gets really cold where you live in the winter, you should probably buy a heater, which is recommended for a tank that's bigger than yours.

For example, I would typically recommend a 25 watt heater for 2.5 gallon and 3 gallon tanks.

If it is relatively warm where you live and there is no cold winter weather, you can get the same heater even for a 5 gallon aquarium.

To be safe, you probably shouldn't get less than 50 watts of heating power for a 5 gallon tank.

That doesn't mean the heater is too powerful for your little 5 gallon tank.

The thermostat will command the device to turn off when it has finished its work.

More power just means that the heating unit is more than capable of maintaining a reasonable water temperature for your little tropical fish in cold weather.

You could literally put a 200 watt heater in a 5 gallon aquarium and everything will be fine.

However, it is important not to overestimate the heating capacity of the heater, as on a cold night the unit will not be able to heat the tank to full capacity and your fish could get sick.

To be on the safe side, I prefer a heater rated at least 50 watts on 5 gallon or larger tanks.

The material from which the heater is made is important, but it is not the key to success.

You might remember the old days when all we had were glass tube heaters.

Today there are many more materials, shapes and sizes for aquarium heaters.

In addition to aquarium heaters made of glass, there are also those made of titanium and stainless steel.

But should you care about the material of your aquarium heater?

To be honest, I never worried about it.

As long as my little heater did its job, everything would be fine.

Of course, there are some differences between the 3 types.

Glass heaters, for example, always come in tube form, which may be impractical for some people and the way they view the inside of their aquarium.

Also, despite the fact that most glass warmers are made from fused silica or some other unbreakable glass, my experience is that glass is at least breakable.

When it comes to price, glass aquarium heaters usually cost less than the other two types.

Still, cheap glass heaters may come with less accurate thermostats and have a shorter lifespan.

Stainless steel and titanium heaters have a longer lifespan than other shapes and also cost a little more.

That said, their water temperature readings are more accurate and they often come equipped with a temperature controller, giving you more flexibility in regulating the climate in your small aquarium.

Do you really need an aquarium heater for such a small space?

If you want to keep tropical species like betta fish in your small aquarium, thenIt is desirable to have a water heater there..

Most tropical fish require a water temperature range of 25 to 30°C.

These water temperatures typically cannot be achieved or maintained in an aquarium if you live in a non-tropical climate.

But the main reason you want a heater on your small tank is this:

An aquarium heater with a thermostat ensures a stable water temperature throughout the day.

Fluctuations in aquarium water temperature between day and night can lead to weakening of tropical fish.

This can lead to various types of deadly parasitic beings that are not easy to cure.

Preventing deadly disease outbreaks in freshwater and saltwater aquariums is the best reason to buy an additional heater for your aquarium.

Avoid even the slightest possibility of failure when starting an aquarium

Of course, the heater you end up buying for your small aquarium will play a key role in the well-being of your tropical fish.

But have you taken the remaining steps to create a healthy and suitable environment for your pets?

Most victims of pets and new failures in the aquarium.they are not related to the heaters in your aquarium, but to the fact that there was no established nitrogen cycle in the system.

"Cycling" an aquarium means that you have been waiting for a long timespecial groups of beneficial bacteria that settlein water and the nitrogen cycle begins.

A functioning nitrogen cycle allows your fish to stay alive and not be poisoned by their own waste in the water as these bacteria break it down.

This is especially important with small amounts of water, such as those in small aquariums under 5 gallons.

This process takes some time and is not the most fun.since you can't have fish in the tank before the cycle or they could die.

Increasing the nitrogen cycle in an aquarium takes 8-10 weeks.

Fortunately, you can shorten the cycle time to just 2 weeks by adding some bacteria from the bottle.

Ohelpful bacterial supplementsyou get the right bacteria in the tank and the tank starts working almost immediately.

And that's what it's about. Which water heater did you finally choose?

Leave me a comment below if you have something to share or want to ask me a question.

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