Some coldwater fish species like rainbow shiner and cherry shrimp don’t need a heater as long as you maintain the room at a stable temperature.
However, if you have tropical fish in your aquarium, a heater is a must-have. Tropical fish thrive in temperatures between 24°C and 27°C. You’ll need a heater with an internal thermostat that keeps the aquarium at a constant temperature.
In this buying guide, we recommend the best aquarium heaters you can buy online in the UK. We also have a few pointers on what to look for when shopping for an aquarium heater.
If you are in a hurry, please see below a quick summary:
Best Aquarium Heaters (UK Market)
Our Top Pick
|Interpet Deltatherm Aquarium Fish Tank Heater
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For Small Tanks
|XiLONG Aquarium Heater Small Fish Tank Heater
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Extra Large Tanks
|Eheim Aquarium Thermostat Heater
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|Uniclife 25 W Submersible Aquarium Heater
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|hygger 300W 500 Watt Aquarium Heater
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Key Considerations When Choosing an Aquarium Heater
Wattage is the most important feature to consider when buying an aquarium heater. Wattage determines the amount of water – and thus the size of aquarium – that the heater can heat comfortably and efficiently.
Oversizing or undersizing an aquarium heater are both bad.
A heater with wattage that’s too small for your tank will struggle to keep water at the right temperature, and will likely stop working before long. But the biggest danger is the water temperature dropping too low and threatening the life of your fish.
A heater with a wattage that’s too high is a waste of energy. A too-powerful heater can also be potentially dangerous for your aquarium if it breaks and doesn’t stop heating when the water reaches the right temperature. It’ll quickly overheat the water, putting your fish in danger.
Here are the best wattages for different aquarium sizes. Note that these are just general recommendation. Max capacity varies among different brands, even those with the same wattage.
- 4-30 litres – 25W
- 23-45 litres – 50W
- 45-90 litres – 100W
- 68-135 litres – 150W
- 90-180 litres – 200W
- 135-270 litres – 300W
As you can see, each wattage covers a pretty wide range of fish tank capacity. To further narrow down the ideal wattage, consider by how many degrees you need to raise the water temperature.
Subtract the room’s average temperature from the target aquarium temperature. For instance, if the room stays at around 20°C and the target fish tank temperature is 24°C, you need to raise water temperature by 4°C.
In that case, you can be conservative with the wattage. For a 90-litre aquarium, a 100W heater will do. But if the room is colder than 20°C, go with a higher wattage. For a 90-litre fish tank, a 150W or 200W heater is ideal.
If the room temperature is similar or slightly higher than the ideal aquarium temperature, you don’t need a heater. In fact, you may need an aquarium chiller if the room temperature climb too high.
B. Type of Heater
Submersible heaters are the best. Because both the heater and thermostat are underwater, the aquarium stays uniformly warm without hot or cold spots. A submersible heater will also do a better job keeping the aquarium at a precise temperature range.
On the downside, submersible heaters don’t last long.
External heaters have the control module outside the tank (hang on the tank or some other surface), with only the heating coil or tube going into the water.
To ensure uniform and accurate heating, we recommend getting an external heater with a separate submersible probe that monitors water temperature.
The main advantage of external heaters is the ease of monitoring and adjusting aquarium temperature. Most of these heaters have a large display that shows the current temperature.
C. Temperature Range
The typical temperature range for most aquarium heaters is 16°C to 32°C, which covers the ideal temperature for most fish and coral aquariums. Here is a selection of thermometers that will help you check the temperature.
D. Indicator Light
It’s a small thing, but an indicator light showing the heater is on is a big deal. It gives you peace of mind, knowing that the heater is functional.
By monitoring the indicator light, you can also tell if you got the right wattage. If the light keeps going on and off frequently, the heater may be struggling to maintain a stable temperature. Buy a higher wattage heater or add a second heater at the other end of the aquarium.
Make sure the heater is safe for your fish. Many submersible heaters have a glass exterior that prevents fish from getting shocked or burned.
Another great safety feature is overheat protection, though you’ll find it only in premium aquarium heaters. This feature turns off the heater automatically if the water temperature rises beyond a certain point. This can save your fish if the heater breaks and keeps heating the water beyond the set temperature.
- Tip: When ordering an aquarium heater, also get an aquarium thermometer. If the heater is faulty and overheats the water or doesn’t heat it well enough, you won’t know if you don’t have a thermometer. A thermometer is an extra layer of security that ensures the heater is working as intended.
Having a thermometer also lets you test the accuracy of the heater. If, for instance, the heater happens to be a couple degrees off, you’ll know to set it a couple degrees higher or lower to achieve the right temperature.
Top 5 Reviews
1. Interpet Deltatherm Aquarium Fish Tank Heater
If you have a large aquarium with up to 270 litres of water, the Interpet 300W Deltatherm heater is a great choice.
It is a submersible style heater. Use the included suction cups to position it diagonally in the water. Keeping it in a diagonal position increases accuracy, ensuring your fish tank stays at the right temperature.
The heater comes already set at 24°C, but you can adjust temperature anywhere between 16°C and 32°C.
An on/off indicator shows when the heater is working. The light will come on when the water temperature drops below the set point and turn off when the water reaches the proper temperature.
The heater is surrounded by heat and shock resistant glass, so it’s safe for fish.
2. XiLONG Aquarium Heater Small Fish Tank Heater
If you have a smaller fish tank with between 40 and 60 litres of water, the XiLONG 50W aquarium heater is perfect.
It’s designed specifically for smaller tanks. You can set the temperature between 17°C and 35°C depending on what you have in your aquarium.
To ensure durability and safety, the heater is surrounded by shock and heat resistant glass. A double layer of insulation protects fish from the heating element.
The cable is 1.4m long and includes a standard 3-pin plug.
The submersible heater includes an indicator light that lights up when the heater is working and turns off when the water reaches the set temperature.
3. Eheim Aquarium Thermostat Heater
The Eheim aquarium thermometer is another good choice if you are looking for a high-wattage heater for a large aquarium.
Eheim recommends the 300W heater for fish tanks between 600 and 1,000 litres. That’s much higher than what most manufacturers recommend. But customers who’ve used it say it heats that much water without a problem.
The Eheim uses its outer glass jacket to heat more water than comparable aquarium heater do. The glass increases the heating surface area and improves heat distribution. In addition, it protects fish from shock and heat.
The Eheim heater is a submersible style. Suction cups are included for installation against the side of the tank. Plug in the 170cm cable and then select the ideal temperature between 18°C and 34°C.
An on/off indicator will tell you when the heater is working.
4. Uniclife 25 W Submersible Aquarium Heater
The Uniclife 25W submersible aquarium heater is designed for small 5-gallon (19 litres) fish tanks.
Using the red knob at the top, You can set the temperature between 20°C and 34°C, a smaller range than most aquarium heater, but still adequate for tropical fish.
Thick quartz glass distributes heat evenly while protecting fish from heat and shock.
The heater goes under the water. Use the included suction cups to secure it against the side of the tank. Once you set the right temperature, the internal thermostat will cycle the heater on and off to maintain that temperature. An indicator light comes on when the heater is working.
Included with the Uniclife heater is a stick-on thermometer you can use to monitor the temperature of the water. Stick the thermometer on the outside of the tank.
The thermometer is a great idea, but we don’t recommend using it. Stick-in thermometers are not accurate. Instead, get a proper submersible thermometer, either an analogue one or a digital model with a submersible probe.
5. hygger 300W 500 Watt Aquarium Heater with LED Digital Temperature Controller
The hygger aquarium heater is a step up – in both design and price – from basic aquarium heaters.
Instead of the usual submersible tube design of other heaters, the hygger consists of an LED display with a heater element and probe attached to it using cables.
Only the heater element and the probe go into the water. The display stays outside. The cables are long enough, giving you flexibility on where to position the display.
The display shows the current water temperature. A temperature control button lets you set the target temperature between 16°C and 32°C.
The heater will maintain this temperature. Whenever the probe shows a 1°C drop in temperature, the heater comes on and turns off again when the probe registers the set temperature.
The biggest praise from aquarium owners using the hygger heater is how accurate it is. Most aquarium heaters tend to be a couple degrees off. The hygger heater is right on the mark most of the time. This ensures your aquarium maintains the right temperature.
The heater includes overheat protection. If, for some reason, the water reaches 36°C, the heater will automatically turn off and the screen will flash to alert you.
The heater is rated at 300W, enough to heat 110-220 litres of water. For large aquariums, there’s a 500W option that heats 220 to 450 litres of water.