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To keep your fish happy and healthy, maintain a consistent water temperature. Without this, fish are more susceptible to becoming sick and have less control over algal growth within the tank. Selecting the correct aquarium heater is not a technical decision, rather one that directly impacts the success of your tank, both short-term and long-term.

The most common choices are the submersible aquarium heater and the external aquarium heater. Both maintain the optimal temperature of your water, but you must decide upon one or the other based on the installation, the overall stability of water temperature, and the appearance of your setup, in addition to a few other features to maintain long-term usage of the heater.

Quick Answer

Submersible heaters are the internal aquarium heater, which work great for beginner or average aquarium-keepers and are very user-friendly and inexpensive.

External heaters are also referred to as in-line aquarium heaters. They work outside the aquarium, connecting to a filter, and offer the most stable temperatures and the cleanest-looking aquarium possible. These heaters are a great choice for aquascapers.

Choose a submersible aquarium heater if you want simplicity. Choose an external aquarium heater if you prefer stability and a clean aquarium look.

What is a Submersible Aquarium Heater?

Submersible heaters are designed to be put inside the aquarium with the fish and plants. They usually are sealed with glass or quartz, which surrounds the heater and its thermostat. The water outside of the aquarium heater is heated, and it then disperses to heat the rest of your water.

Most people prefer to place the submersible heater near the output of the filter to distribute heat throughout the aquarium quickly.

Why Is This the Hobbyists' Choice?

Hobbyists choose this type of aquarium heater because they are easy to install in aquariums and work with just about every tank without having to be hooked up to a filter system.

What is an External Aquarium Heater?

External or in-line aquarium heaters hook up to an existing filter system (commonly a canister filter) on your aquarium. This filter will pull the water out of the tank and run it through the aquarium heater and then back into the tank.

The result is a closed system that heats water while it is circulating through the filter.

Why Do Advanced Aquarists Prefer External Heaters?

Advanced aquarium keepers love the external heater because all of the equipment is hidden from view within your aquarium's decor. This provides a cleaner look and allows the temperature of the tank to be controlled very evenly across the entire aquascape, which is extremely beneficial in planted or display tanks.

The Difference Between Submersible and External Aquarium Heaters

Temperature Stability: Which Type of Aquarium Heater is Better?

Temperature stability is a major factor when looking at aquarium heaters.

Submersible heaters depend on water flow. If the flow of water in the tank is not strong enough, zones of different temperatures may occur within the tank.

External aquarium heaters fix this issue because they heat the water in the filter. The heater also connects directly to the filter, so the temperature is evenly dispersed throughout the tank in a closed system.

The takeaway:

• Submersible: good (with flow)
• External: best (in most systems)

Visual Appeal: Clean Aquascape Vs. Practical Aquarium Set-Up

The biggest visual difference between these two types of aquarium heaters is quite evident. Submersible heaters are very noticeable in any tank and often can distract from a beautifully designed aquarium layout, if one even wishes to keep their aquascape well hidden, as some would even hide these from view behind decorations and plant life.

External heaters, however, are a great choice for those individuals who want to hide all of the bulky, unattractive equipment that is commonly placed within aquarium tanks; this is especially desirable to anyone wanting to set up a display aquarium or for someone interested in aquascaping. These heaters will be connected to your filter and out of sight at all times.

Safety and Longevity

When used correctly, the external and submersible aquarium heaters are equally safe.

Submersible Heaters:

• Will remain inside the aquarium and, therefore, is always susceptible to being damaged.
• Can shatter and harm your fish from being broken, as well as cause potential damage to your fish when temperature changes.
• Be sure to always put the heater where fish will not be in contact with it.

External Heaters:

• No risk to fish at all, as it sits outside the aquarium.
• You do have to watch out for damage and leaks from connecting and removing pieces from the filter and plumbing system; this can even kill your fish, as well as cause a water spill.

In summary:

• Submersible aquarium heater: Simple and cheap, but physically in the tank.
• External aquarium heater: High maintenance and system dependent, but out of sight.

Energy Efficiency and Performance

Energy output and overall efficiency between the two heaters are both extremely similar within typical home aquariums with properly sized heaters. However:

External heaters are more efficient at consistently warming water due to the continuous filter loop; this provides even and constant heat within the tank.

Submersible fish tank heaters will more commonly "cycle" on and off as their placement affects the rate of heating; thus, the efficiency will vary depending on how well the water is able to flow throughout the entire tank.

It does not seem to matter so much the efficiency within tanks smaller than 150L.

Installation and Maintenance

Installing a submersible heater is as simple as possible. You simply place the aquarium heater inside your tank, ensure that it is fully submerged in the water, plug it in, and set the temperature. The maintenance involves giving it a quick wash and scrub if anything builds up on it, and also checking if there is any water that leaks out from the bulb if you are using the submersible aquarium heater.

As it was discussed previously, external heaters require quite a bit of additional work to get them set up in your filter and outside of your aquarium. They do require regular checking for any possible plumbing leaks and ensuring they are in the correct direction before turning on any water. Once they are set up, it is much easier to do maintenance on them in contrast to a submersible heater.

Which is Right for You?

Use a submersible heater if:

• You are an intermediate beginner who has been into fish tanks for only a short while.
• You want an inexpensive aquarium heater.
• You have small to medium aquariums that you don't necessarily want to maintain to perfection.

Use an external heater if:

• You want to put together an aquascaped or planted display aquarium.
• You own an existing canister filter that you want to attach to.
• You have sensitive fish or a display aquarium that requires consistent heat levels, and you also desire a clean, minimal look.

Mistakes to Avoid

When buying an aquarium heater, you do not necessarily need to worry about getting a heater type over another, but rather the right size and placement. Undersizing your aquarium heater and letting it run to heat the water consistently instead of heating at the best intervals will drain more energy. Bad flow in your aquarium will also reduce any type of heater’s efficiency.

Conclusion

Both external and submersible aquarium heaters work best depending on the tank in which it is placed and the overall usage that the heater will be subjected to. The submersible heater works well with more basic set-ups, while external aquarium heaters fit better with display, aquascaped tanks that often have advanced set-ups with extensive filtration and plumbing work.