Can An Aquarium Heater Be Too Powerful? (Different Tank Sizes And Their Suitable Heaters)

Tank Sizes And Their Suitable Heaters

Aquarium Heater is a very important aspect of fishkeeping.

In fact, without it, it will be very difficult or nearly impossible to keep fish and other aquatic animals in the aquarium.

An aquarium heater is an electronic device that generates heat, which is used to keep the aquarium water warm so that it could be suitable for many tropical aquatic animals that we keep.

Being an electronic device, its size and watts vary, some are very suitable for small fish tanks while some are very suitable for medium size tanks and some are okay with large tanks, etc.

Knowing that they vary in both size and watts ( power) people often ask if a heater could be too powerful for a fish tank or Aquarium.

An Aquarium Heater could be too powerful when it is used in a much smaller tank than the original size of the tank it was designed for.

Although many people do not agree with this, citing that they have used a much bigger heater when their former heater broke down, etc.

Well, let’s reason this logically, every heater has its watts and size and they are designed for a specific size of tanks.

Imagine using a heater that was designed to function very normally in a 200-gallon tank in a 20-gallon tank, what do you think will happen?

In such a case the heater will be very powerful and might even take the temperature of a such small fish tank to 89—95°F and above which will kill every living thing in such a tank.

If you do it the other way round by keeping a heater that was designed for a 20-gallon tank in a 200-gallon tank, the heater will not be very effective, as it will take more time to keep the temperature normal because there is more water in the tank than there is in a 20-gallon tank.

Don’t let anyone deceive you by keeping a powerful heater in your small fish tank because it might not end very nicely. After all, you will be struggling to keep the water temperature down.

Also, a heater could be less powerful if you keep a small heater in a larger tank.

Is It Okay To Oversize An Aquarium Heater?

Oversizing Aquarium Heater simply has to do with keeping a bigger heater in a smaller fish tank. Is it advisable?

It is okay to keep an aquarium heater in a fish tank that is slightly more powerful than it, but it is not advisable to keep an aquarium that is far more powerful than a fish tank in it.

It is okay to oversize an aquarium heater, but it all depends on if the heater is designed for far bigger tanks because if it is, then it is not recommendable as your aquarium could be boiling in no distance time.

I don’t even recommend getting a fish tank heater that is even a little bit more powerful or bigger than your fish tank, just keep to the watts that were designed for your fish tank and you will be totally fine. Also, make sure you have more than one heater just in case of an emergency.

Can I Put A 100 Watt Heater In A 5 Gallon Tank?

A 100 Watt aquarium heater is too powerful to be kept in a 5-gallon tank.

It will boil the water in the tank which will kill every living thing in it.

As I explained above, every tank size has its specific or suitable heater according to wattage, for instance, a 25-watt or a 50-watt heater will be totally fine with a 5-gallon tank or 10-gallon tank, and anything more powerful than this could be very powerful in a such small tank.

Despite that, I strongly believe that every tank should have a suitable watt, in some cases, it is okay to have a heater its watt is a bit bigger than your fish tank if you live in a very cold climate and if your room temperature is very cold.

So, if you are thinking of keeping a 100-watt heater in a tiny tank such as a 5-gallon tank, 10-gallon tank, or even a 15-gallon tank, it is not advisable.

What Size Heater Do I Need For A 2.5 Gallon Fish Tank?

The suitable heater for a 2.5-gallon fish tank is 20 watts heater, and if you live in a cold climate, 25 watts is very okay for a 2.5-gallon fish tank.

A 2.5-gallon tank is a very tiny tank to use a 25+ watt heater on unless you live in a region where the temperature is always cold and freezing, and even if you live in a region where the temperature is normal, you can switch to 25 watts once it starts snowing and everywhere is freezing.

What Size Heater Do I Need For A 3 Gallon Fish Tank?

Any heater that is below 50 watts is very suitable for a 3-gallon fish tank, depending on the climate.

Although a 20 to 50 watts heater could serve but it all depends on the weather condition of the region where you live, and again if your room has a heater or not.

What Size Heater Do I Need For A 1.5 Gallon Fish Tank?

A suitable heater for a 1.5-gallon fish tank shouldn’t be more than 25 watts.

What am trying to say is that a 25 watts heater and below will serve very well in such a tiny fish tank. Again, it depends on the climate.

How Many Watts Should A Heater Be For A 20 Gallon Tank?

The Perfect heater for a 20-gallon fish tank is a 100 watts aquarium heater.

100 watts is very perfect for a fish tank of this size, but as I always say, it depends on both the climate of the region and the temperature of your room, so you might want to get a bit more powerful heater than 50 watts if the climate or the room temperature is lower than normal.

How Many Gallons Will A 200W Aquarium Heater Heat?

A 200-watt aquarium heater is very suitable for a 50, 60, and 70-gallon fish tank.

200w is okay for these tank sizes but 250w could also serve 65 to 75 and even 80-gallon tanks.

How Many Watts Should My Fish Tank Heater Be?

I believe that this article will not be complete without elaborating in detail the actual watts of a heater your fish tank needs, so here they are:

  • 5-10 gallons = 50watts
  • 20 gallons = 100watts
  • 25-40 gallons = 150 watts
  • 50-60 gallons = 200 watts
  • 75-100 gallons = 250 or 300 watts


Each Aquarium Heater is designed for specific watts which is suitable for specific tank size and it could be powerful when it is kept in a tank size that is smaller than the size it was designed for.