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Best Heater For 20 Gallon Tank: Reviews & Guide To The Right Type

20 gallon aquariums are a great community tank but need the right type of heater. So let’s find the best heater for 20 gallon tank setups!

By Matt Thomas
Last updated on

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Best Heater For 20 Gallon Tank

20 gallon aquariums can be great community tanks, especially for beginners, due to their relatively small size. But they still need to be heated accurately and consistently. So how do you find the best heater for 20 gallon tank setups?

After extensive assessment, we chose the Orlushy 100W Submersible Aquarium Heater as the best value for 20 gallon aquariums. Its stable mid-range temperature and affordability make it a fantastic choice.

But we’ve also assessed a range of other options. So whether you’re on a budget, or want a premium digital heater, we’ve done the hard work here to help you make the right choice.

Just take a look below!

  1. Best Value: Orlushy 100W Submersible Aquarium Heater
  2. Best Budget Preset: Tetra HT 100W Submersible Aquarium Heater
  3. Budget Analog: HITOP 100W Adjustable Aquarium Heater
  4. Best Consistent Analog: Fluval M100 Submersible Heater
  5. Best For Easy Calibration: Fluval E100 Electronic Heater
  6. Best Premium Digital: Cobalt Aquatics 100W Flat Neo-Therm Heater
  7. Best For Readability: Marineland 100W Precision Heater

Best Heater For 20 Gallon Tank Setups Reviewed

We’ve assessed the heaters below for their suitability for your 20 gallon aquarium across several key criteria. This includes power, accuracy and temperature stability, ease of installation and use, and safety features.

1. Orlushy 100W Submersible Aquarium Heater


  • Heater Type: Submersible, adjustable
  • Dimensions: 9.5 (length) inches
  • Wattage: 100 Watt (other wattages available)
  • Key Features: Temperature range of 68 to 89°F, 2mm thickened shatterproof quartz glass, built-in thermostat, separate digital thermometer included, 6 ft power cord
  • Best For: Value

Orlushy’s 100 Watt Submersible Aquarium Heater is affordable yet tough. Featuring shatterproof 2mm thickened quartz glass you can be confident that you won’t have any breakages as long as you keep it fully submerged.

At just 9.5 inches long, the 100 Watt heater will easily fit your 20 gallon aquarium and can be mounted vertically or horizontally. So you’ll have space for plenty of plants and a community of fish.

The large control knob is mounted at the top for easy access. And the dial is marked with clear 2-degree increments, making it easy to read and set the temperature. 

Several owners note it runs best towards the middle of its 68 to 89°F temperature range, and we found it could be a little inconsistent if you try to run it close to 89°F. Orlushy does provide a separate digital thermometer though which you can use for further accuracy.

Overall many owners praise this heater for its ability to maintain a consistent temperature, particularly in the mid-range, its durability, and affordability.

  • Affordable
  • Toughened glass to prevent cracks
  • Small size and long 6ft power cord
  • Heating indicator light and separate digital thermometer
  • No heater guard
  • Less accurate at top of temperature range
  • Suction mounts can break easily

2. Tetra HT 100W Submersible Aquarium Heater


  • Heater Type: Submersible, preset
  • Dimensions:  8.25 (l) x 3.5 (w) x 1.63 (d) inches
  • Wattage: 100 Watt (other wattages available)
  • Key Features: Preset temperature of 78°F, active heating and temperature reached indicator lights, built-in electronic thermostat
  • Best For: Budget Preset

If you’re new to fishkeeping the 100 Watt preset Tetra HT Submersible Aquarium Heater is a great option. It’s set at 78°F, which is perfect for many tropical fish. And as there’s no need for adjustment it’s incredibly easy to use.

At 8.25 inches in length, it will easily fit your 20 gallon aquarium. And it’s fairly slim too at 1.63 inches in depth. So you can easily hide it in the corner of your tank behind a few plants if you want it out of sight.

The indicator light is simple, and unlike many other analog heaters it shows active heating (red light) and temperature reached states (green light). This makes it really easy for you to see that it’s working properly.

Its built-in electronic thermostat maintains a consistent temperature close to 78°F, generally with only +/- 2 degrees of inaccuracy. But some owners have noted concerns about overheating so always keep a separate thermometer in your tank too.

  • Easy to use with no adjustment needed
  • Clear indicator lights show active heating and temperature reached
  • Compact
  • Stable temperature at 78°F (+/- 2°F)
  • Preset so cannot be adjusted
  • A few reviewers concerned about overheating

3. HITOP 100W Adjustable Aquarium Heater


  • Heater Type: Submersible, adjustable
  • Dimensions: 8.8 (length) inches
  • Wattage: 100 Watt (other wattages available)
  • Key Features: Temperature range of 68 to 93°F, built-in thermostat accurate to +/- 2°F, LED heating indicator, 2mm thickened quartz glass, stick-on thermometer included
  • Best For: Budget Analog

Our budget analog choice is the HITOP 100W Adjustable Aquarium Heater. It’s one of the lowest-priced adjustable heaters on our list, yet at 100 Watts still has the power needed to heat your 20 gallon aquarium consistently.

At just 8.8 inches long it will easily fit the back panel of a shallower 20 gallon long tank. And with a temperature range of 68 to 93°F, it can be adjusted to suit most tropical fish. Some owners note it can run 1 or 2 degrees high, so always use a separate thermometer to check.

HITOP provides a separate stick-on thermometer with the heater, so although you’re likely to need to upgrade it can be useful for a quick check. There’s a large adjustment knob on the top, but it only has a +/- rather than a numerical dial so can be difficult to accurately set.

The LED heating light shows when the unit is actively heating so you can easily check to see if it’s working. Overall many owners praise the HITOP for its consistency (once you allow for +/- 2 degrees) at an affordable price.

  • Affordable
  • Clear indicator light showing active heating
  • Separate stick on thermometer provided
  • Stable temperature once set
  • +/- dial only with no temperature increments
  • Tendency to run 1 or 2 degrees high

4. Fluval M100 Submersible Heater


  • Heater Type: Submersible, adjustable
  • Dimensions: 11.0 (length) x 1.0 (diameter) inches
  • Wattage: 100 Watt (other wattages available)
  • Key Features: Temperature range of 66 to 86°F, easy control temperature dial, computer-calibrated thermostat, ceramic heat sink, heating indicator light, shock-resistant glass
  • Best For: Consistent Analog

Fluval’s M100 Submersible Heater is compact yet powerful. At 11.0 inches, it’s the same length as the 50 Watt heater, so will easily fit in a 24.0 (l) x 12.5 (d) x 16.5 (h) 20 gallon tank. The slim 1.0 inch diameter also leaves plenty of swimming space for your fish.

With an adjustable range of 66 to 86°F, you can support cooler water fish or those that prefer warmer water like Gouramis. And we found the 100 Watts of power to easily maintain a consistent temperature around 75°F, even if the room gets cooler at night.

The adjustment control is easy to turn, and because it’s mounted on the top it’s easy to read and access without reaching too far inside your tank. The dial shows the temperature in 3-degree increments making it easy to set accurately too.

Whilst it’s a glass heater the M100 is made of borosilicate [1], making it shock resistant and more durable than some glass heaters. So as long as you keep it fully submerged you won’t have any issues with cracks or breakages.

The M100 has an indicator light so you can see when it’s actively heating, making it easy to watch for any faults. But it doesn’t have an overheat or auto shut-off if allowed to run dry, so keep it below the water level at all times.

  • Easy to install with pre-attached mount
  • Borosilicate glass for durability
  • Slim and compact
  • Easy to access and read temperature control
  • No heater guard supplied
  • Lacks overheat or run-dry sensor

5. Fluval E100 Electronic Heater


  • Heater Type: Submersible, adjustable, digital/ electronic
  • Dimensions: 11.75 (l) x 2.0 (w) x 1.12 (d) inches
  • Wattage: 100 Watt (other wattages available)
  • Key Features: Temperature range of 68 to 93°F, adjustable in 1°F increments, two digital temperature sensors, LCD screen with VueTech color alert system, fish bumper guard
  • Best For: Easy Calibration

The first digital aquarium heater in this list is the Fluval E100. This 100 Watt model provides the power needed to heat your 20 gallon tank and is adjustable from 68 to 93°F. So you can provide the right environment for a range of tropical fish.

It’s really easy to calibrate and is accurate too. The temperature toggle and digital LCD display allow you to adjust it in 1°F increments, so it’s great if you have fish that are very sensitive to temperature changes.

The E100 is fully surrounded by a tough plastic bumper guard which not only protects your fish from the heating element but also stops the glass tube from getting knocked. And at 11.75 (l) x 2.0 (w) x 1.12 (d) the unit will fit well into your 20 gallon tank.

Fluval’s VueTech color alert system is also included on the E100. The LCD display shows green when the temperature is correct, but if it fluctuates by +/- 2°F it changes to blue for too cold or red for too hot. So it’s really easy to see if the temperature is wrong and adjust it.

Some users report difficulty in getting the placement right, as you need to position the controls above the water line and get it near to your filter’s outflow to circulate the warm water. But many praise the E100 for its accuracy and consistency in maintaining a stable temperature.

  • Accurate and consistent temperature
  • Easy to calibrate and adjust
  • Clear LCD display with temperature fluctuation alerting
  • Robust bumper guard
  • 5-year warranty
  • No run-dry sensor
  • Initial placement can be difficult

6. Cobalt Aquatics 100W Flat Neo-Therm Heater


  • Heater Type: Submersible, adjustable, digital/ electronic
  • Dimensions: 9.75 (l) x 2.25 (w) x 1.25 (d)
  • Wattage: 100 Watt (other wattages available)
  • Key Features: Temperature range of 68 to 94°F, built-in thermostat accurate to +/- 0.5°F, touch-button control, set temperature and current temperature LEDs, automated shut-off to prevent overheating, shatterproof casing
  • Best For: Premium Digital

Our alternative choice of digital heater is the 100 Watt Cobalt Aquatics Flat Neo-Therm. It’s freshwater and saltwater compatible and the 68 to 94°F temperature range is accurate to +/- 0.5°F. So it’s a great choice for marine fish that need warmer, precise temperatures.

The easy-to-use touch button control makes adjusting the temperature straightforward, and the LED gauge shows the set temperature alongside the current temperature in 2°F increments. This makes setting and monitoring your tank’s temperature really simple.

At 9.75 (l) x 2.25 (w) x 1.25 (d) the Neo-Therm is ultra-flat and modern. But you can easily hide it behind plants if needed, leaving plenty of room for your fish. It also automatically shuts off if the temperature gets too high. So there’s no danger of harming your fish.

While this heater carries a premium price, many owners praise it for its consistency in maintaining a stable temperature. And along with the 3-year warranty you can be confident the Neo-Therm will provide reliable heating for your tank for years to come.

  • Highly accurate and stable temperature
  • Easy touch button control
  • Flat, modern design to save space
  • Overheat auto shut-off
  • 3-year warranty
  • Premium price

7. Marineland 100W Precision Heater


  • Heater Type: Submersible, adjustable
  • Dimensions: 11.69 (l) x 3.94 (w) x 1.63 (d) inches
  • Wattage: 100 Watt (other wattages available)
  • Key Features: 65 to 89°F temperature range, adjustable temperature dial in 1°F increments, Thermal Switch overheat protection, mica core heating element, mounting bracket with 3 window positions
  • Best For: Readability

Marineland’s 100 Watt Precision Heater is one of the easiest analog heaters to adjust and read. The set temperature is shown on the top dial and down the side of the heater, and the mounting bracket has 3 window positions. So you can easily see the temperature from any angle.

At 11.69 inches long it will fit the back wall of a 24.0 (l) x 12.5 (d) x 16.5 (h) 20 gallon tank at a slight angle. And its slim 1.63-inch depth means it won’t get in the way of your plants or fish.

The adjustment knob allows you to set the temperature in 1°F increments and makes an audible ‘click’ for each degree. This makes setting the temperature easy although it can sometimes be out by 1 or 2°F, so use a separate thermometer in your tank to check.

There’s an indicator light showing when it’s actively heating your water, as well as a Thermal Switch that automatically cuts off the heater if it goes above a preset maximum. This means your tank won’t be in danger of overheating.

Marineland Precision Heaters have a mica core heating element to help with heat transfer and, like many owners report, we found it to hold a steady temperature. Coupled with the lifetime warranty you get a lasting product.

  • Clear temperature display can be viewed from multiple angles
  • Can adjust in 1°F increments for accuracy
  • Thermal Switch for overheat protection
  • Lifetime warranty
  • May run 1 or 2°F off from the set temperature

What To Consider When Looking For The Best Heater For 20 Gallon Tank Setups

Before choosing the best heater for your 20 gallon tank, you’ll need to consider several factors.

Zebra danios in  aquarium

Does Your 20 Gallon Fish Tank Need A Heater?

While some cooler water fish, such as White Cloud Minnows, are small enough to be kept in a 10 to 20 gallon aquarium, most species for a tank this size will be tropical. So you’ll need a heater to maintain your tank’s temperature anywhere from 74 to 80°F.

Maintaining a consistent, stable temperature is key. So even if your average room temperature is suitable for part of the day, any change in the evening or at colder parts of the year can cause your fish to become less active and sometimes lead to disease.

Consider The Type Of Fish You Keep

While many tropical fish do best around 74 to 80°F this can vary, so you should always research your chosen species. Some, like Zebra Danios, can be more tolerant to fluctuation, whereas guppies need a stable temperature around 77°F.

Look for an adjustable heater if you have fish that are particularly sensitive to temperature changes as it means you can set it with a high degree of accuracy. Some digital aquarium heaters are even accurate to +/- 0.1°F.

Power And Wattage For Your 20 Gallon Aquarium

The power of your heater is measured in Watts (W), and in general, it takes about 2.5 to 5 Watts to heat 1 gallon of water [1]. So a 75 to 100 Watt heater is the best choice for most 20 gallon aquariums.

Using the slightly higher value of 5 Watts per gallon above allows your heater to deal with cooler temperatures, for example in winter months. As long as your heater has a built-in thermometer it will automatically shut off once the right temperature is reached.

Room Temperature And Fluctuations In Your 20 Gallon Aquarium

Your room temperature can also affect the power your heater needs. If you live in a cooler climate with a room temperature of 60 to 65°F, you may need a heater of 125 Watts.

A 20 gallon aquarium has a higher thermal capacity than the water in a smaller nano aquarium, so whilst it will take a little longer to heat up the temperature won’t fluctuate as much. Even so, it’s important to use a good-quality heater to keep it consistent.

Space And Placement Of Your Heater

There’s generally plenty of space for a heater in a standard rectangular 24.0 x 12.0 x 17-inch 20 gallon fish tank. And as many heaters for this size of tank have a maximum length of around 12 inches you shouldn’t have any issues getting it to fit.

You should usually place your heater close to your filter’s output to ensure proper circulation of heated water. But pay careful attention to your heater’s instructions. Some submersible heaters recommend placing them horizontally for best performance.

How Many Heaters To Use

For larger 40 gallon fish tanks and above, some aquarists recommend using two heaters positioned at either end. Not only can this help heat the water evenly, but if one fails the other can act as a backup.

But a single heater of the correct wattage is the best option for your 20 gallon aquarium. This will help maintain the required 74 to 80°F range without taking up valuable swimming space.

submersible aquarium heater

What Is The Best Type Of Heater For A 20 Gallon Tank?

While there are a number of aquarium heaters available, there are two key types that are suitable for your 20 gallon fish tank.

Submersible Aquarium Heaters

One of the best heater types for 20 gallon tank setups, submersible aquarium heaters usually consist of a coiled metal heating element inside a glass or metal tube.

As they are designed to sit fully submerged below the water line they are highly efficient at maintaining the correct temperature and heating your tank evenly. But ensure you keep them submerged as glass models can shatter if they run dry.

Immersible Or Hanging Heaters

These heaters are designed to hang off the back of your tank with the heating element below the water line. As they are not fully submerged they are less efficient at keeping your water at a consistent temperature than submersibles.

They can also be difficult to position and make opening the hood of your tank difficult as the controls hang off the rim. Although immersible heaters sometimes come as part of smaller starter kits, they are much less common for a 20 gallon tank.

Heaters Not Suited For 20 Gallon Tank Setups

We’ve also outlined other types of heaters you may encounter that we don’t recommend for 20 gallon fish tanks, along with the reasons below.

In-Line And In-Sump Heaters

Rather than sit inside your fish tank, in-line aquarium heaters are installed on the outflow line from your external filter or sump. While this gives more room inside your tank, in-line heaters are generally designed for larger aquariums and often have a wattage of 200W or above.

As the name suggests, in-sump heaters sit inside your sump which is a smaller tank often used to filter your water in a larger saltwater aquarium setup. Whilst some aquarists use sumps with 20 gallon aquariums they are much more common for larger tanks.

Substrate Heaters

If you own a heavily planted tank, such as one used for aquascaping, a substrate heater can be used as a secondary heater. They consist of a heating wire that’s fixed to the bottom of your tank underneath the substrate.

These heaters only heat the substrate, so while they are good for promoting plant growth by creating circulation within it, they will not provide enough heat for your fish.

They’re also hard to maintain if you have a fault as you’ll need to remove your substrate.

Filter Heaters

Some larger external filters come with built-in heaters. These units filter your water and heat it at the same time before returning it to your tank.

However, filter heaters are rare and are generally used in tanks larger than 20 gallons. They also often struggle to maintain a consistent temperature throughout your tank.

How To Choose The Best Heater For 20 Gallon Tank Setups

After considering the basic requirements such as wattage and type of heater, use this guide to discover the additional features you should look for.

Cherry barb aquarium fish

Temperature Range, Adjustability, And Consistency

When it comes to choosing the best heater for 20 gallon tank setups you’ll find plenty of choice whether you are looking for a preset or adjustable heater. Preset heaters are easy to use and don’t need calibrating, but you are restricted to a constant temperature, usually around 78°F.

Many 100 Watt adjustable heaters for 20 gallon fish tanks have a temperature range of about 65 to 95°F. So you can switch from keeping cool water fish, like White Cloud Minnows at 64-72 °F, to killifish that prefer 73-77° F without changing your heater.

Do check the reviews for your chosen heater before buying. In general, adjustable heaters tend to be better at keeping a consistent temperature than preset ones. But it very much depends on the quality of your chosen heater.

Accessible Controls And Readability

Although it’s easier to reach inside your 20 gallon aquarium to adjust your heater than it can be in a larger 55 gallon tank, you should still ensure the controls are accessible and easy to adjust.

Analog submersible heaters often have a large control knob at the top, so look to make sure it’s easy to rotate and set. Many of these heaters also have an indicator dial showing the temperature in 1-degree increments so you can easily see what you’ve set it to.

Digital aquarium heaters can be even easier to use as their controls are often placed on the cable outside the tank. They tend to have clear LED or LCD screens so you can even check the temperature from across your room.

Safety Features

Submersible heaters tend to be one of the best heater types for 20 gallon tank setups in terms of safety. As they sit fully below the water line there is less chance of them being incorrectly positioned and so running out of the water than immersible ones.

But the best heaters for 20 gallon tanks have further safety features like auto shut-off sensors which detect if the temperature is too high or the water level is too low. This stops your heater from running dry and prevents the risk of shattering.

If your chosen heater doesn’t have a full LCD display, at a minimum make sure it has an indicator light that shows when it’s actively heating. This makes it easy to tell when your heater is running and helps identify any faults.

Materials, Durability, And Price

Analog submersible aquarium heaters are often made of a metallic coil or quartz core, surrounded by a glass exterior. These heaters can be very durable as long as you always keep them submerged so they don’t shatter.

Digital aquarium heaters can sometimes be made of metals such as titanium. This makes them highly durable although they tend to be more expensive.

For example, a 100 Watt analog submersible heater for a 20 gallon fish tank may cost around $20 to $35. A digital heater with the same wattage, can cost around $55 to $65.

Our Verdict

The best heater for 20 gallon tank setups can depend on several factors. Like whether you own a freshwater or marine tank, or if you prefer a digital or analog heater.

Our favorite is the Orlushy 100W Submersible Aquarium Heater for its durability and ability to maintain a consistent mid-range temperature in a 20 gallon tank.

But if you want an ultra-precise digital heater the Cobalt Aquatics Flat Neo-Therm is a perfect choice. Or if you’re on a budget the HITOP 100W Adjustable Aquarium Heater gives consistent heating at an affordable price.


Check out the answers to some of the most frequently asked questions when it comes to choosing the best heater for 20 gallon tank setups.

What Is The Best Heater For 20 Gallon Tank Setups?

The best heater for 20 gallon tank setups is a 100 Watt submersible heater like the Orlushy 100W Heater, which gives consistent heating at an affordable price.

Do I Need Multiple Heaters In A 20 Gallon Aquarium?

A single 100 Watt heater is the best choice. Whilst two heaters are a good way of evenly heating a larger tank, this isn’t needed for a 20 gallon aquarium and takes up space.

How Long Will It Take My 20 Gallon Tank To Heat Up?

A 20 gallon tank may initially take around 24 hours to fully heat up the first time you install your heater, depending on your room temperature.

How Do I Set Up And Calibrate My Heater?

Preset heaters can be switched on and left to reach temperature. Adjustable heaters may also have a separate calibration dial allowing you to accurately set the temperature.

Photo of author
Matt Thomas
Matt has been keeping fish since junior high when he used to look after his parent's tank. He loves guppies, cichlids, and his crowntail betta named Bobby.

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