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Best Aquarium Heaters of 2021

Want to make sure your fish thrive in your aquarium? Keep the temperature consistent and choose the best aquarium heater from our review.

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Best Aquarium Heater Reviews of 2021

Best-in-class
AQQA Submersible Heater

AQQA Submersible 100W/200W/300W/500W/800W Aquarium Heater

Best for tropical aquariums

A digital external controller with LED indicator light helps you monitor the aquarium temperature.

Check price on Amazon

1 AQQA Submersible Heater Review

Are you looking for the best aquarium heater for your tropical environment? Then the AQQA could be the best you can grab. What makes it perfect for the task is the digital controller and an integrated thermostat.

The controller not only lets you set and monitor the temperature but also alerts you of any significant changes. In this way, you’ll be able to maintain a healthy environment for your tropical fish and marine plants.

Tropical fish aside, this heater is also perfect for all other aquarium types, thanks to the generous temperature range between 59°F and 93°F.

Coming in various sizes between 100W and 800W, the AQQA heater is suitable for larger aquariums. The 100W model is perfect for tanks between 25 and 35 gallons, but for a larger ecosystem up to 220 gallons, you can opt for a higher power.

Best value
Fluval M 200W

Fluval M Submersible Heater

Freshwater and saltwater heater

This powerful heater is suitable for tanks of up to 65 gallons and all kinds of environments.

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2 Fluval M 200W Review

Whether you’re keeping cold water or tropical fish, the Fluval M 200W could be the best aquarium heater if you don’t want to break the bank. Suitable for aquariums up to 65 gallons, it outputs a power of 200 watts and is also available in other sizes for smaller or larger tanks.

Although it doesn’t have AQQA’s fancy controller, this unit is as easy to use as it gets. All you have to do is turn the dial to set the temperature and mount it on the aquarium wall or floor. Like AQQA, this is a fully submersible model designed to do everything else on its own, thanks to the integrated thermostat that delivers outstanding temperature control.

Design-wise, we like its reflective finish that mirrors the aquarium’s interior and blends seamlessly into your underwater décor. Discreet, easy to use, and durable, this aquarium heater brings unrivaled value for money.

Also great
Cobalt 31004

Cobalt Aquatics 31004 Neo-Therm Heater

Very flat design

Shatterproof and fully submersible aquarium heater is ideal for smaller tanks.

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3 Cobalt 31004 Review

The Cobalt Aquatics Neo-Therm makes a great alternative to our best-value pick if you’re looking for a reliable heater in the 25-300 watts range.

Despite its heftier price, this aquarium heater offers better temperature control, with heat ranging from 66°F to 96°F and an accuracy of only plus or minus 0.5°F.

A convenient LED indicator shows both the temperature of the water in the tank and the set temperature, allowing for quick control of the parameters.

An integrated thermal protection circuit ensures safety and reliability, turning the unit off if it overheats. Ideal to use in terrariums, freshwater, and saltwater, this aquarium heater withstands all demands.

Best budget
FREESEA Heater

FREESEA 25/50/100/200/300 Watt Aquarium Heater

Best for small tanks

Automatic temperature control allows you to set this aquarium heater and forget it – it will keep the water temperature on its own.

Check price on Amazon

4 FREESEA Heater Review

The FREESEA 100 might not be the most performing aquarium heater out there, but it’s affordable, and it does the job. Suitable to use in fresh and saltwater environments, it is an excellent choice for aquariums of up to 25 gallons.

You can also find it in lower wattage versions for smaller tanks; no matter which model you buy, the heater is easy to set and comes with a digital thermometer for accurate temperature control.

The build quality isn’t exceptional, but as long as you don’t submerge the main control panel, everything should be fine. All in all, this is a great choice for fish keepers on a budget.

1. When to use an aquarium heater?

Many novice fish breeders and amateurs believe an aquarium heater is only useful when growing tropical fish. But even if cold water fish withstand water at room temperature, they can only thrive in water kept at a constant temperature.

The environmental temperature is subject to fluctuations, and a sudden drop of even 1°F in the temperature of the water can compromise the health of your pets. Some species are more resistant than others, but in broad terms, too many temperature fluctuations can easily eradicate the entire population in your tank.

An aquarium heater, therefore, serves two major purposes:

  • Heating water above room temperature for tropical fish.
  • Keeping water at constant temperature, either for cold water or tropical fish.

2. Types of aquarium heaters

Essentially, there are six types of aquarium heaters:

  • Hanging heaters: Are the most common and the most inexpensive type. They often come as part of aquarium kits for beginners and are very easy to install. In fact, you only have to hang them on the edge of the tank, as their name implies. They consist of a submersible glass tube and an aerial head, which may require you to cut an opening in the hood of the aquarium. Most hanging heaters are inappropriate to use in saltwater.
  • Submersible heaters: Are designed to be fully immersed in the water, a design feature that increases both their efficiency and safety. They can be positioned either horizontally or vertically and at any height in the water, as long as you mount them on the tank’s wall with suction cups. Most models come with built-in thermostats that regulate water temperature accurately. It is not recommended to mount these heaters on the gravel, as the glass could shatter.
  • Substrate heaters: Are perhaps the least popular and consist of a coil or wire grid which must be buried in the gravel or aquarium substrate. This type of heater doesn’t warm up the water, but the substrate, which then radiates heat into the water. These models are also equipped with thermostats and are particularly suitable for the tanks which contain many plants.
  • Filter heaters: Come integrated into aquarium filters and heat water during the filtering process. These heaters offer a great solution for the smaller tanks in which a submersible or hanging heater could take up too much space.
  • Sump heaters: Like the filter heaters, these ones come integrated into the sump of a trickle filter and ensure a safer environment, as they are harder to get damaged by a fish or when the aquarium is cleaned.
  • In-line heaters: Are self-contained external heaters that work in tandem with a water pump which moves water through them, getting it warmed up. Some in-line heaters don’t necessarily require a flow of water and can also be used to heat the environment in a terrarium.

3. Aquarium heater power & wattage

Size matters when it comes to aquarium heaters. A too small heater size will be incapable of warming the water in a large tank; likewise, a too large heater size can transform your aquarium into a boiling pot.

Options range from small 25-watt units to 1,000 watts. The heater must match the size of your tank. Otherwise, it could be ineffective.

How many watts does your aquarium heater need?

Experts advise calculating a power between 2,5 and 5 watts per gallon of water when choosing the best aquarium heater. To make things easier, check the chart below for the most common sizes:

Aquarium size

Heater power

10 gallons (40L)

50 watts

25 gallons (100L)

125 watts

50 gallons (200L)

250 watts

100 gallons (400L)

500 watts

200 gallons (750L)

1,000 watts

400 gallons (1500L)

2,000 watts

4. Aquarium heater placement

Depending on the size of the tank and preference, you can place the heater either at the side of the tank or in its middle. Perhaps the best place for your heater is near the water inflow and outflow, to maximize its efficiency.

Heater placement considerations

There are also a few other things to account for when choosing the right location.

  • Make sure you leave enough space between the heater and other surfaces. Otherwise, the fish could get caught between the heater and other elements.
  • Make sure your submersible heater is not touching the gravel or substrate. This could cause a gradient temperature in the heater which could shatter its glass, exposing your fish and yourself to severe injury or death through electrocution.
  • Ensure there are plenty of hiding spaces for your fish, so they won’t be tempted to hide behind the heater.
  • Before turning on your heater for the first time, keep it in the tank for at least half an hour to avoid exposing the unit to sudden temperature changes that could shatter the glass.

5. Fixed vs. adjustable temperature heaters

Aquarium heaters can have either a fixed or adjustable temperature. Most fixed temperature heaters are designed for tropical fish tanks in general, warming water to temperatures in the 78°F range. This temperature, however, is not suitable for cold water fish.

Some species, such as Gold Fish, Bloodfin Tetras, and White Cloud may not tolerate temperatures so high, and in this case, an adjustable temperature heater could be a better choice.

In broad terms:

  • Cold water fish thrive at temperatures from 60 to 72°F.
  • Tropical fish require temperatures between 72 and 80°F.

Passionate hobbyists and business owners would benefit most from an adjustable temperature heater which allows to adjust the temperature to suit different biotopes or to manipulate breeding.

6. What water temperature in a biotope aquarium?

Biotope aquariums recreate natural habitats for cold water or tropical fish to thrive. These aquariums typically require specific temperatures which closely simulate the real temperatures of the water in the area where your fish come from. For example:

  • Amazon biotope aquariums: Are typically populated by fish like the Peruvian angelfish and False rummynose tetra fish. These aquariums thrive at warmer temperatures in the 82°F range.
  • Reef biotope aquariums: The best thing to do is to set the water at a temperature level close to the water temperature in the area where your corals come from. For instance, Indo-Pacific and Caribbean corals have a temperature between 82 and 89°F.
  • Lake Malawi biotope aquariums: Populated with colorful Peacock cichlids and Mbuna fish, these habitats require a water temperature between 72 and 82°F.

7. What other features to consider?

Besides all the above, the best aquarium heaters come with a series of other features that add safety and ensure a smoother operation.

  • Perhaps the most important feature is a thermostat designed to keep water temperature constant.
  • Invest in an aquarium heater that is easy to maintain and clean.
  • An overheat shutoff function helps save your fish if the unit overheats and also prolongs the unit’s lifespan. An automatic restart when the heater cools off also ensures all its functions are reassumed in a timely manner.
  • Also, check the materials the heater is made of. Choose one that is resistant to corrosion and pH fluctuations.
  • An indicator light lets you know whether the unit is heating the water or is in standby. Some of the best aquarium heaters indicate both the temperature in the water and the set temperature, allowing for a better control of the parameters.

8. The Best Aquarium Heater for the Money

Best value
Fluval M 200W

Fluval M Submersible Heater

Freshwater and saltwater heater

This powerful heater is suitable for tanks of up to 65 gallons and all kinds of environments.

Check price on Amazon

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