Setups

Aquarium Heater Size—What Size Heater Do You Need in a Fish Tank

The temperature of your aquariums is an important factor in the and comfort well being of your fish because unlike humans and other mammals, fish do not produce their body heat.

The must rely on the temperature of your aquarium water to maintain their body heat.

That said, to keep your fish tank at the proper setting for your pets, you’ll need to get an appropriate size heater.

But how do you know what size heater to get?

First, to select the right aquarium heater size, you need to know how many gallons of water your fish tank holds. Once you’ve established that, a good rule of thumb to follow is; a heater with an output of 3 to 5 watts of power for every gallon of water you have.

This means a 10-gallon aquarium would require a 25 to 75-watt heater, while a 75-gallon tank will need 250 to 350 watts. A 50-gallon aquarium will then obviously fall anywhere between (at least)100 watts and 250 watts.

It is also important to note that most aquarium heaters range from 25 watts to 300 watts, so for a nano fish tank you’d have to make do with 25 watts aquarium heater. You can use more than one heater in large aquariums.

Keep reading for more insight on aquarium heater size, wattage, best types, and much more.

But first…

Is it Necessary to Have a Heater in a Fish Tank?

Most freshwater fish tanks need heaters for fish to survive, though it will depend on the fish you plan on keeping.

When keeping tropical fish, you will want to add a heater in your aquarium to ensure the water does not get too cold for the fish, and the temperature remains steady even during the colder seasons.

On the other hand, cool water aquarium fish do not require a heater because these species are capable of withstanding a wide range of temperature, and are mostly hardy in just about any region.

Having said that, if you plan on keeping tropical fish, ensure your aquarium remains above 72° F.

Tropical aquarium species include some of the most popular in the hobby including betta, gouramis,neon tetras and most cichlids.

Sub tropical species will survive in slightly lower temperature settings and are mostly native to Florida, Arizona, Southern China, and Indian Northern highlands where it’s warm in summer and cold in winter.

A few fish can tolerate cold water and survive without a heater in the aquarium, they include goldfish, zebra danio, bloodfin and Bueno Aires tetras, dojo loach, white cloud mountain minnow, rosy red minnow, green barb, gold barb, and rosy barb.

Aquarium Heater Size Guide

As I have briefly explained above, the size of the aquarium heater you purchase will depend on the size of your fish tank.

Even so, please note that while most heaters rating are for specific fish tank sizes, what matters more is wattage per gallon.

The precise size of your heater will also be determined by the quality and efficiency of your equipment among other minor variables.

That said, a cheaper, bigger heater may not always be the best for your fish tank. It is sometimes better to go for a smaller, high-quality aquarium heater, but we’ll look at that a little later.

Let us first establish what heater wattage is and how that informs the aquarium heater size to use.

How Many Watts Should Your Aquarium Heater Be?

The number of watts your aquarium should have is dependent on the fish you are keeping and the size of your fish tank, though other factors come to play.

The length, height, and width of your tank, plus the type of aquariums heater you purchase will also dictate the wattage.

Usually, heater with a low wattage below 50 watts are only ideal for small aquariums mostly ranging from 3 to 10 gallons in size.

High wattage filters are best in large aquariums (from 75 gallons) and usually range anywhere from 250 watts. Still, some fish tanks are quite large and could require more than one heater.

That said, a 50 watts heater is adequate for a 20 gallons aquarium in a warm room (78° F), but the efficiency goes down in a colder fish tanks to only being useable in a 15-gallon fish tank.

Here is a concise breakdown of aquarium heater wattage depending on the fish tank you have.

  1. For a 20 to 30-gallon aquarium, use 50 to 100 watts heater. Use 100 watts heater in a 30- gallon if you live in colder regions where the room’s temperature often dips to below 70° F. A 75 watts is adequate for a 30-gallon in a fairly warm aquarium room, but also useable in a 20-gallon tank in cool to a moderately warm temperature. Consider a 50-watt unit only for a 20-gallon in a generally warm room or for a smaller fish tank (less than 20 gallons).
  2. A 100 watts to 200 watts heaters are ideal for aquariums that are 50+ gallons, with tanks that are between 50 and 65 gallons and housed in normal to warm room temperature best with a unit closer to 150 watts (medium). In these conditions, even a 75 gallon can be operated with a 200 watts unit.
  3. 300 watts heater are appropriate for aquariums above 100 gallons, with the rang anywhere from 100 to 125 gallons.
  4. Any aquarium above 125 gallons would require a heater with more than 300 watts output. Good high wattage heaters include Finnex Titanium tube which can produce up to 500 watts and Hydor Theo which give out up to 400 watts.
  5. Very-large aquariums may require you to install multiple heaters to keep your fishes comfortable. If you have a 300-gallon size tank, for instance, you will need a 300 to 500 watts heater which you can easily attain with two 200 watts heaters on either side of your fish tank.
  6. In conclusion, use the 3 to 5 watts per gallon rule in case making a choice gets too challenging, Also, go for quality before quantity to get the best value for your money.

Where Should You Put Your Aquarium Heater?

For the best functioning of your aquarium heater, you’ll need to place it strategically. Otherwise, you may have the correct size heater but not get the best out of it.

The best location is near the water flow, such as adjacent the filter outlet (or inlet) or in a stream of a powerhead. Of course, this is assuming your unit is not an under-gravel (substrate) heater.

Placing your heater close to the water flow ensures the heat produced is properly and evenly distributed across your fish tank by the water current.

However, in larger fish tanks, it is always better to use two heaters placed on opposite ends for maximum heat distribution.

Submersible aquarium heaters can be installed horizontally near the bottom of the tank for best heat circulation, or vertically if that is your preference. Plus keep decorations away from the heating unit for the water to circulate freely.

Moreover, provide enough space between the heater and the substrate or the sides of your aquarium to ensure no fish get stuck against the heater and get burned.

To best access the functioning of the heater, you’ll also need an aquarium thermometer.

But where do you place it!

Well, this may vary, but one thing that is for sure, your thermometer should be above the gravel line to get accurate water readings.

Floating and standing thermometers should go inside the tank opposite the heater, while stick-on thermometer goes to the outside of an aquarium. They can either be placed at the back or side of the fish tank.

Generally, avoid placing thermometers close to the heater to make sure the readings are not higher than the actual aquarium temperature. Also, do not place them in direct sunlight or near a heating or cooling unit.

What Heater Do You Need for Your Fish Tank?

Apart from using the right filter size and positioning it correctly, you’ll need to understand different types of aquarium heaters before making a purchase.

The type of heater you want for your fish tank should be able to keep the temperature above 72° F and up to 82° F in cold weather. It should be able to sustain 3 to 5 watts of power for every gallon of water in the fish tank.

That said, there are several types of aquarium heaters, each with pros and cons. Below are the most common types.

#1— Submersible Aquarium Heater

Submersible aquarium heaters are units that can be fully immersed in water and are arguably more efficient than other fish tank heaters like the hanging types.

These filters can be placed pretty low in the tank if need be and can be positioned either vertically, horizontally or even at an angle, though they work best when not slanting.

Because most submersible heaters use a thermostat, I recommend placing them horizontally to help the thermostat get an accurate reading of the tank temperature and correctly activate and deactivate your heater.

Also, since most are not free-floating, you need to attach them on your aquarium glass (preferably at the back) near an area with adequate water flow for optimum circulation.

Use clips and suction cups to hold the heater in place.

Like all heaters, keep your submersible unit away from the gravel as the difference in heat conductivity between the water and substrate could result in your aquarium glass cracking.

You may come across in-sump heaters, which are nothing more than a submersible aquarium heater that is set up in the sump of a trickle filter, rather than inside a fish tank. The configuration provides better safety for your fish and increases your heater’s longevity.

#2— Inline Aquarium Heaters

Generally, inline heaters are electric and feature a high output heat source which heats fluids pressed through the device.

Aquarium inline units are self-contained external units that reside in or along a section of external piping, mostly filter plumbing or other pieces of external aquarium equipment.

Inline heater require a water pump to move aquarium water through them, though they also piggyback on trickle and canister filter or UV sterilizers.

That said, you will also get some built-in inline heaters that come combined with a filter (mostly canister and power filters). They warm the water as it goes through the filter, returning heated and clean water to the tank.

#3 — Undergravel (substrate) Aquarium Heaters

A substrate heater consists of a long cable that is set in curved lines at the bottom part of an aquarium. The unit heats up directly at the cable loops creating water circulation in the base tank area.

Even so, undergravel will heat your fish tank but they are not meant to raise your water temperature, at least not like conventional heaters.

Instead, they serve as microcirculation systems at the base of a tank, to wash nutrient-rich water to plant roots through the substrate.

Because of this, substrate filters are only ideal for planted aquariums.

Moreover, because the heat is likely to get trapped at the bottom, undergravel heater cables are only suitable for gravel size 0.8mm or more.

That’s all!

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

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