How To Choose The Best Aquarium Heater

Aquarium heaters are one of the most important pieces of equipment that we use so making the right choice is crucial. With so many different options available it can seem a minefield but there are some simple steps that can make choosing the perfect heater a simple task.

In this article we won’t be focusing on brands because they each have their own merits and it really comes down to personal choice although I would advise you to avoid the cheap unbranded options available on certain sites as they may not have passed our strict UK safety checks.

As a general rule of thumb, you can’t go far wrong if you aim for 1 watt of power per litre of water. I.e. a 100w heater would be perfectly suitable for a 100L aquarium. This formula tends to be roughly in line with manufacturers recommendations.

There are however lots of other factors that come in to play. For example, the temperature of the room that the aquarium is situated in. If your target water temperature is 25°C and the room temperature is 22°C then a smaller heater would do the job perfectly well. However, if the room is very cold then you may need more wattage per litre of water.

You may have noticed that opting for a larger heater often doesn’t cost much more than its smaller counterparts. This is because the bulk of the cost of manufacture is in the thermostatic controls and the building of the device itself. A larger heater only requires a longer heating element, therefore the cost of increasing wattage is fairly low.

With this in mind you may be wondering why not to just buy the most powerful version. Well there are some very good reasons why you shouldn’t.

Firstly, when heaters fail it tends to be the thermostat that goes wrong rather than the heating element. This commonly results in the heater becoming stuck on and not turning off once the water has reached the desired temperature. If you’re using an overpowered heater then the water temperature will rapidly rise giving you little time to notice or react to the issue. This risk can be further reduced by using two heaters rather than one. For example, if you decide that you need 200 watts of power to heat your aquarium then it’s better to use two 100w heaters. If one gets stuck on then it’s very unlikely to heat up sufficiently to cause serious harm to your fish before you notice the problem.

Secondly, there is a much greater chance of large fluctuations in temperature. In the same way as a kettle will boil much faster with a small amount of water, an oversized heater will rapidly heat a smaller body of water.

Finally, larger wattage heaters are often much larger than lower wattage versions. This makes them difficult to position correctly and discretely in a small aquarium.

To summarise, I advise that you stick to these basic guidelines

  • Avoid cheap unbranded heaters
  • Aim for 1 watt of power per litre of water
  • Don’t be tempted to opt for a larger heater than you need
  • Where possible use 2 smaller heaters rather than 1 large one
  • Always have a thermometer in the tank and check it regularly

Click here to take a look at our range of heaters


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