The right aquarium heater is vital for keeping your tropical fish happy and healthy. But, with so many to choose from, how do you select the best one?
The task is easier when you know the essential features to look for when shopping for an aquarium heater, so I put all the information you need right here in this guide.
Inside, you will find why an aquarium heater is crucial, the types available, my recommendations for both small and large tanks, the features to watch out for, and how to set up the heater in your tank.
By taking a few minutes now to read this complete buyers guide, you’ll be able to shop with confidence for the best aquarium heater for your needs.
Why You Need an Aquarium Heater
The number one reason you need an aquarium heater is to keep the fish healthy.
Most fish sold are tropical, which means they come from an environment where the waters are, on average, between 72-82 degrees Fahrenheit.
A heater is necessary to keep your tank water temperature at an optimal level for your species of fish. Even if your house remains a toasty 72-degrees all year, the water inside your tank may not be warm enough to keep your fish happy and comfortable.
When the water gets too cold or hot, the delicate environment inside your tank changes, and your fish can become lethargic, quit eating, and become sick or die.
Even slight fluctuations in water warmth, as can happen overnight when outside temperatures drop, can stress your fish and lead to problems.
Installing a quality aquarium heater helps you avoid harming your fish since they not only maintain a proper temperature inside your tank but also should include features for safety and convenience to make using them simple.
How do I know which size aquarium heater I need?
Aquarium heaters come in a vast range of sizes, which can be confusing for beginners just entering the world of tropical fish ownership.
If you are planning to upgrade to a new tank, your old heater may not suffice if the aquarium is even a few gallons bigger than the old one.
The rule for selecting the correct size heater goes as follows:
- Differential between target temperature of tank VS average room temperature
For rooms that are no more than 8-10 degrees cooler than the ideal temperature for your tank, you will need a heater size between 2.5 to five watts per gallon of water volume inside your tank.
For example, a 10-gallon tank will need a 25-50 watt heater. The wattages increase as the temperature difference between tank and room increases.
When room temp versus tank temp range farther apart, the wattage of your heater will also need to increase. That same 10-gallon tank may need a 75-watt heater instead.
Also, each brand of aquarium heater may not work as efficiently as another with the same wattage. These issues can make finding the right heater size frustrating.
Luckily, every heater should have a chart with per gallon recommendations for safe use. If your tank size is at the upper range of any level of wattage, always choose the next larger size to ensure you’ll be getting enough power to keep your water temp constant.
Another important note is that huge tanks, typically those that are around 100 gallons on up, will need two or more heaters to maintain a constant temperature. Choosing heater size will require combining the power of separate units, for total wattage.
Types of heaters
Aquarium heaters come in different styles, which I go over below. Base the style you choose on the size and shape of your tank, but be aware that the most commonly sold heaters for aquariums are submersible.
In-line heaters sit outside the tank between the glass and the filter system. This style of heater requires more space around your tank and usually offer a higher wattage than is recommended for smaller tanks.
Immersible, or hanging heaters, are very common but are slightly less efficient at providing a consistent heat in the tank versus other styles. They are easier to check and maintain since it sits higher in the tank.
In-sump heaters set inside the filter system and have similar issues as the in-line heater, with size and high wattage a problem for installation on small tanks.
A substrate heater is a cable that lays on the bottom of the aquarium underneath the substrate. The interior of the cable generates heat, which then warms the tank.
Most of the time, this type of heater is recommended for planted aquariums since it creates a vertical current in the water that drives nutrients to the plants’ root system.
Best Aquarium Heaters for Small Tanks
Sometimes a heater, while suitable for any size tank, works best in a small tank. My top picks below are for aquariums between 3 to 10-gallons in size.
For betta tanks under three gallons, I give you a favorite pick as well.
1. Cobalt Aquatics Flat Neo-Therm Heater
The Cobalt Aquatics Flat Neo-Therm Heater comes in a nice range of wattages and does a great job keeping the temperature of the water within half a degree.
Temp range: 66-96 degrees Fahrenheit
Size: Slim and flat, so it’s easy to blend it into tank decor
Installation and use: Easy to install and control
The heater features a user-friendly control system that shows the tanks current temperature along with the set temperature so you can quickly monitor performance. The LED display is bright, which helps in reading the numbers any time of day or night.
When it comes to safety, the unit is shatterproof and offers a built-in thermal protection device, so the heater automatically shuts down if it detects overheating.
Drawbacks: A bit pricey and the attachment cups lose suction if you move them about too often.
2. Hygger Submersible Aquarium Heater
At 50-100 watts, the Hygger Submersible Aquarium Heater is no-nonsense, affordable, and attractive while also delivering consistent results.
Temp range: 75-91 degrees Fahrenheit
Size: Slender and fairly short, vertical or horizontal mount
Installation and use: Easy installation, difficult to read (see details)
The unit heats until the water is 1.5-2 degrees above your set temp, shuts off until the temp drops to 1.5-2 degrees below that number, and then kicks on again. When the unit is heating, the LED indicator light turns red.
For safety, overheat protection turns the unit off if the water hits above 97-degrees Fahrenheit and the heater will also turn off if a ground-fault occurs.
Drawbacks: The controller is not digital, so you must rely on a separate tank thermometer to read actual water temperature.
3. Freesea FS-28 Small Aquarium Heater
The Freesea FS-28 heater comes in under 7-inches long for the 25 and 50-watt models which is ideal for small tanks.
Temp range: 63-95 degrees Fahrenheit
Size: Short and oval, so it takes up less room in small tanks
Installation and use: Simple installation. Control of temp takes some trial and error.
The heater automatically cycles on (indicator light is red) and off when it hits the temperature setting you choose. You will need a separate thermometer to monitor tank temperature. This unit comes with a round LED thermometer, but the size is better suited to larger tanks.
The oval shape of the heater is safer for fish because there are no sharp edges that can snag on fins or scales. You can mount the heater either vertical or horizontal, as long as you submerge it completely.
For safety, the heater does offer automatic shut off in the event of overheating.
Drawbacks: The thermostat is manual, which can be challenging to pinpoint the exact temp degree you want. Users recommend initially setting it lower and slowly raising it to the desired temp by watching a separate tank thermometer.
Tanks Less Than One Gallon
Tiny aquariums may need heating as well, so choosing a model made for betta fish is the way to go if your tank is less than two gallons.
4. Marina Betta Submersible Heater
I like the Marina Betta Submersible Heater that utilizes 8-watts of power to keep your fish comfortable.
Temp range: No range, just continual low-level heat output
Size: Small, about 4 inches tall and two inches wide
Installation and use: Easy to install but must monitor temp manually
This type of heater, prevalent for betta and small tanks, is an “always-on” unit. There is no thermostat or settings, just a constant heat that needs monitoring with a standard aquarium thermometer.
If you see the water temp getting too warm, you need to unplug the heater until it cools down since there is no on/off switch. Some users find using an outlet timer in tandem with this heater is very useful in keeping the tank water at optimal warmth.
Best Aquarium Heaters for Large Tanks
1. Fluval E Electronic Heater
At 100-300 watts, the Fluval E Electronic Heater is an affordable option that delivers consistent results.
Temp range: 68-93 degrees Fahrenheit
Size: Long and slender, with vertical or horizontal mounting
Installation and use: Easy to install, read, and control
Once you set the temperature you desire (Farhenheit or Celcius), the readout will change color if the water goes up or down more than two degrees, which lets you know at a glance is something is amiss. The display will flash if it detects a change of more than 5.5-degrees F in either direction.
The mounting bracket is very convenient. You can pop the heater on or off for tank cleaning and place it at any angle for optimal viewing of the backlit LCD. The fish guard keeps even the little guys away from the heater core to prevent injury.
For safety, the heater warns you if water flow decreases and will shut off if the water level gets too low.
On the downside, you may need more than one of these for big tanks, and the length may pose a problem in some fishscapes.
2. Hygger Titanium Aquarium Digital Submersible Heater
The Hygger Titanium Heater provides a lot of versatility as it’s suitable for both saltwater and freshwater aquariums that need between 50-500 watts of power.
Temp range: 32-104 degrees Fahrenheit
Size: Slim and short for easier placement in tank
Installation and use: Medium effort to install and program the temp, yet easy to read/control
The heater comes with an external thermostat and thermometer you can wall-mount or hang from your tank. Just program in the temperature you desire, and the unit will turn on and off to keep the water no more than one degree below your setting.
The separate thermometer is sensitive and can detect a -68℉ to 140℉ temperature range, with an accuracy of 0.2℉ plus or minus, so you can trust the readings.
The materials are very durable and rust/corrosion resistant for a long life, which makes this model cost-efficient.
Drawbacks: The manufacturer suggests you mount the heater horizontally near the water intake for best results, which may not work for your tank’s “style” or shape. The heater is also not made for plastic or acrylic tanks, nor use in-line with a sump.
3. Aqueon Pro Adjustable Heater
The Aqueon Pro Heater is a favorite for its design and thermoplastic cover that is shatterproof and much safer for fish that swim near. It also offers an excellent range of wattages aside from this 250-watt version so that you can pinpoint the best size for your aquarium.
Temp range: 68-88 degrees Fahrenheit
Size: Slim and black, so it blends into tank decor
Installation and use: Easy to install but takes practice to master the temp setting
This heater is of a super durable, non-corrosive thermoplastic, so you know it will last a long time. The material is also beneficial since it disperses the heat evenly along the surface without getting so hot it could burn your fish.
The control knob sits above the surface of the water, making it easy to change settings when necessary without having to remove it from the tank. There are two light indicators, red for when it’s heating and green when not so you always know there is power to the unit.
For safety, the thermostat automatically turns off if the heater does not detect water, but will reset and resume operation once set back into the aquarium.
Drawbacks: To set the temperature, you use a dial, not a digital readout, which makes it difficult to know the exact degree you have it set on.
How to Install and Use an Aquarium Heater
You and your fish will get the most benefit out of your aquarium heater when you know the correct way to install and operate it.
Always read the instructions/manual that comes with your heater in its entirety, even if you have years of experience with fish tanks.
While most heaters should be set near the water filter intake/output flow for better heat distribution around the tank, there may be some models that suggest different placement.
For large tanks, it’s sometimes best to have two heaters, one on both ends of the tank for better heat control. Consider this option if your tank is around 50 gallons or more.
Most heaters come with a mounting bracket or, more typical, suction cups to hold the heater in position. Make sure the surface of the tank under the suction cups is clean of debris, or the heater will pop loose.
Once the heater is in place, run your cords to an edge or wall and bring them up and over the tank wall so you can plug the unit in. Always wait until the heater is in place and completely underwater before plugging it in.
Once you attach the heater to the tank, it’s time to program the settings.
The aquarium size, your ambient room temperature, and the type of fish you own will determine the suitable temperature setting for your heater. Again, read the manual for your particular heater’s setting control instructions.
Set the temperature and turn on the heater.
Set a thermometer as far away from the heater as you can to guarantee you are getting a proper reading of the overall tank temperature.
For the initial few days, heavily monitor your tank temperature and control settings until you reach a consistent heat level.
What to Consider When Choosing a Heater
Next, I go over the important features to look out for when choosing an aquarium heater appropriate for your needs.
The wattage amount determines the ability of the heater to maintain a specific temperature in your aquarium.
As a general rule, you need 3-5 watts per gallon of water. Heater packaging should offer charts that describe appropriate wattage versus tank size choices.
For large tanks, using two smaller heaters instead of one powerful one tends to provide better results if water circulation inside the tank is weak. For example, use two 150-watt heaters instead of one that is 300-watt.
Never use a heater with far more wattage than you need for your tank size since it makes it more likely to overheat the water accidentally.
Adjustable temperature range
Depending on what region the country you live in, the ambient air around your tank can range from cold to hot as the seasons pass.
Being able to fine-tune the water temperature to offset such an issue is critical.
The only way to handle changes with ease is to purchase an aquarium heater with adjustable settings.
For tiny tanks, you are stuck with continual-heat options, where you need to plug and unplug the heater to control the water temp. But, for anything bigger, always choose a heater with the broadest range of temperature adjustment you can find.
Nobody wants to stretch, stoop, or hassle to reach heater controls when they need adjustment.
Substantial control knobs are easier to see and turn than tiny ones. Units that mount the thermostat outside the tank are much more user-friendly than those that the thermostat is directly on the heater. Depending on how you place the heater, you may need to reach to the bottom of your full tank to change the setting.
Take a few moments before purchase to think about where you need to mount a particular model of aquarium heater and where the control access will be once it’s in your tank.
Those few moments may help you avoid months of frustration and wasted money when you find your heater is next to impossible to use.
A very important feature is being able to read the temperature your heater is set and the actual water temperature inside your tank.
The numbers should be large and clear. Either bright white on a dial gauge or crisp LED digital displays with a backlight.
You should be able to read these critical numbers at a glance, without having to perform crazy maneuvers while squinting to attempt to bring them into focus.
TIP: No matter how expensive or accurate a fishtank heater claims to be, always use a separate thermometer as a back-up in case of power outages or malfunctions.
All aquarium heaters will fail sooner or later.
Prolong the life of your heater by investing in the best quality materials and design.
Thick thermoplastic or glass tubes with a durable shroud or cage will reduce the chance of breakage when you move the heater for cleaning or rearranging the tank.
Cords should be long enough to reach outlets safely, with becoming a trip or snag hazard.
The design of the heater should keep the fish and other aquarium-living critters in mind, with shapes to deter bumps and bruising and shrouds or cages to keep fish away from the heating element and safe from burns.
The more safety features your heater provides, the less worry you’ll have that your fish will get an accidental electric shock, or the water will get too hot or cold.
Automatic shut off features are critical for:
- Water level too low
- Water flow is too slow
- Electrical faults
Another nice touch are indicator lights that let you know there is power to the heater and when the unit is in heat mode or not.
Keeping your fish content and strong is the ultimate goal of a fish tank heater, so finding one made of durable material, with convenient controls and settings, in the right shape and wattage is crucial.
Now that this guide explains what you need to look for, the job of finding the best aquarium heater will be less stressful and much more enjoyable!.