Why an Aquarium Heater Should Be Fully Submerged

Aquarium heaters are one of the main components of a tropical fish tank, which happens to be one of the most common kinds of fish that aquarium owners choose. While you may live in a region where the water can be warm enough without heaters, most tank owners are not as fortunate.

When you first have an aquarium, the heating side of things can be the most daunting and lead to items that are overlooked when setting up your tank. With that, we will look deeper and answer this:

Why an aquarium heater should be fully submerged? Although there are different types of aquarium water heaters, such as adjustable and fully submersible. They all have a part of their construction, which has to be covered by water to avoid damage. Aside from this, if the heating element isn’t in the water, it won’t be taking care of your fish and the temperature of the tank.

Are All Aquarium Heaters Waterproof?

The majority of heaters are fully submersible. This means they sit under the water of your aquarium. These will have a minimum water line that is not reached will cause damage to your heater. The best way to situate these is to be sure they are fully submerged in your tank.

Alternatively, there are some which are not submersible. These are not worth bothering with as the issues are more damaging than the underwater type. These will have a maximum waterline, and if the water level goes higher than this, then there can be an electrical short.

Aquarium Water Heater Size and Location

If you don’t live in a cold region, then the size of your aquarium heater should be around 5 Watts for each gallon of water of your tank capacity. A quick example of being a 20-gallon tank requires a 100W water heater.

If your fish tank is more extensive than this, rather than one large heater, you can consider two smaller heaters located in differing areas of your aquarium. A solid example being a 100W heater at either end of a 40-gallon aquarium.

The upside of this being water temperatures will be uniform without cold spots, and, should one fail, your water won’t automatically be cold until you get the broken heater repaired or changed.

Warm Water Distribution

Once your heater is warming the water, heat travels around the tank in various ways. To help with this, you can place your heater as close as you can to the flow of water, and this can be the outlet of your filter or the inlet where return water comes back.

The inlet may be preferable as the temperature will not be lost as the water travels through any media for cleaning.

The ways heat is distributed around your tank are as follows:

  • Conduction: Conduction is when heat spreads from hot areas to colder areas through touch. A warm area will spread to a colder area, although weakening in the process.
  • Convection: As the water warms, it is less dense. This causes it to rise, and where you will get convection currents forming.
  • Circulation: This is where your pump and filter come into play. Heated water is spread around as the water circulates through the system.

With these means of dispersing warm water, there are further means of spreading it around your tank even more.

Some schools of thought suggest placing air stones under the heater. This helps denser, colder water to rise toward the heater where it heats quickly and will spread from the motion of the bubbles.

Another area is to place the heater horizontally close to the filter exit area. The water will hit the heater before falling back into the tank. The issue with this being an issue with your pump. If this clogs or fails, your heater won’t have any surrounding water to keep it cool and prevent it from being damaged.

Things to Consider for Aquarium Heaters

When you have tropical fish, they prefer water temperatures around 74-82F (Fahrenheit). However, you will find it is nearly impossible to maintain a steady temperature unless you reside in the native territory your fish came from.

Your water temperature must remain in this range throughout 24 hours. While there are many calculators you can use on the internet, these are merely a guide. There are though many other things you need to understand so that you can keep your water temperatures at a stable level.

Kinds of fish: There are many species to choose from, and a good many of them like different temperatures, like bettas, angelfish, tetras, and others like their water at an even temperature all the time. Swordtails and barbs, along with others, are a little more durable and can put up with some changes in water temperatures.

Aquarium sizes: Larger tanks are better off with two heaters. It is advisable to place these at either end of your aquarium. It is here where the debate of two heaters comes in. A couple of heaters forces this redundancy while heating all the tank rather than just a portion of one end.

Heater tube size: A heater tube needs to match the height orlength of your tank. Because heat rises, you do need to be sure you cover the depth and length of your tank water. One other area you need to be wary of is the thickness of your aquarium walls. These will also lose heat to the outer atmosphere.

Tank location: This will have a bearing on what you need to set your heater. If your tank is in view of a window, you may set your heater wrong for when it cools at night. Be sure wherever it sits, you keep an eye on the temperatures at different times of the day.

Using Aquarium Heaters and What to be Careful Of

An aquarium heater is like many other pieces of equipment. It isn’t a set it and forget it, because they can fail or break. This results in cold water, or a heater that gets too hot and overheats your fish.

Here are a few things you do need to be wary of when you are purchasing an aquarium heater or setting up your system ready for use.

Purchase a better unit rather than a cheaper heater. If there is an issue, replacing your fish will cost more than a good aquarium heater.

Be sure you read all the instructions because they will contain a lot of information. There are things such as cleaning heaters you need to know about to avoid slat pollution.

Don’t rely on the heater gauge. Always test aquarium temperatures using a thermometer. This is good practice because you are not relying on a source that can give a not so accurate reading.

Consider thermostats or controllers. These will help for the times when you are away from home. Setting a thermostat is a safer way to be sure your tank remains at the right temperature.

Aquarium Heater Types

Getting a heater for your aquarium is crucial for the comfort and well-being of your tropical fish. Fish don’t produce their body heat like humans and other mammals. To keep warm, they rely on nothing more than water temperature.

Types of heaters:

Immersible Heaters

These are the most common, and among the least expensive heaters to purchase. Nearly all aquarium kits have hanging heaters to help fish owners keep the correct water temperature for their fish. These heaters hang off the edge of the fish tank with a glass tube where the heating element sits in the water.

Submersible Aquarium Heaters

These can be fully submerged under the water, where they tend to be more productive than hanging aquarium heaters. You place these low in the water in horizontal, vertical, or angled positions.

Keep the heater off the gravel because the heat conductivity difference could result in your heater glass cracking.

Substrate Heaters

These are among the least common variety and have coils of wire or grid heating elements. This you bury under your gravel or sand. The most significant benefit of substrate heaters comes from when they are used in planted tanks where the gravel acts as a type of insulator and keeps the roots of the plants too cool. The substrate heater solves this problem greatly because the gravel is always kept warm, and the plants’ roots are at a comfortable temperature.

Filter Aquarium Heaters

Some aquarium filter models that you purchase will come with their heater, such as canister filters and sometimes power filters. These heaters will heat the water as it goes through the filter and filters out all the waste. The result is clean and heated water going back into the tank.


It doesn’t need to be difficult using an aquarium heater, as the manufacturer does much of the hard work. Opting for fully submersible heaters can take away some of the minor headaches.

Understanding what temperatures your fish require can be the most challenging aspect of this part of the operation. But, once you get the temperatures right, your fish will think they are at home in their natural habitat.