What Is an Aquarium Fan?

If you keep fish, water temperature matters. An aquarium fan is one way to bring a warm tank down by a few degrees.

What is an aquarium fan?

An aquarium fan is a small electric fan that blows air across the water surface of a tank. The moving air speeds up evaporation, and evaporation cools the water. The effect is modest. Tunze lists a drop of 1.8 to 3.6°F for its Aquawind twin fan, and the JBL ProTemp Cooler is listed as lowering water temperature by 2 to 4°C (3.6 to 7.2°F).

This article answers the most common questions about aquarium fans.

Types of Aquarium Fans

There are a few different types of aquarium fans, but all have essentially the same function: to move air across the water surface so the water cools by evaporation.

Common types of aquarium fans:

• Saltwater aquarium fan
• Marine fan
• Clip-on aquarium fan
• Exhaust fan
• DIY aquarium fan
• Aquarium fan with thermostat
• Aquarium chillers

What Is a Saltwater Aquarium Fan?

There is no separate saltwater type of fan. The same clip-on cooling fans are sold for both kinds of tank. The JBL ProTemp Cooler, for example, is listed for fresh and seawater tanks.

On a saltwater tank, a fan has one extra effect to watch. It makes water evaporate faster, and Bulk Reef Supply notes that only fresh water leaves the tank while the salt stays behind, so salinity rises until you top off. Top off with fresh water, not salt water.

What Is a Marine Fan?

A marine fan is used for cooling down saltwater fish tanks.

Therefore, a marine aquarium fan is just another name for a saltwater fan.

There are different types of marine fans, including small clip-on fans that are designed specifically for smaller tanks to larger fans attached to larger aquariums.

What Is a Clip-On Aquarium Fan?

A clip-on aquarium fan is a small electrically powered aquarium cooling system with a frame, motor, and propeller blades.

You use it much like you would any other type of aquarium fan.

The big difference with this fan is how you attach it to the tank. With a clip-on fan, you attach it to an outside edge of the tank with a clamp.

Check that the bracket fits your tank rim before you buy. The Tunze Aquawind twin fan, for example, fits an aquarium edge up to 25 mm (0.98 in.).

What Is an Exhaust Aquarium Fan?

Some tanks have a canopy or hood that traps warm, moist air above the water. A small fan fitted in the canopy can move that air out.

You can also use an exhaust fan in a canopy above your aquarium.

What Is an Aquarium Fan with Thermostat?

An aquarium fan with a thermostat is designed to control the temperature in your tank.

The thermostat is often a separate controller with a temperature sensor that sits in the tank.

It switches the fan on when the water rises above the set temperature and off again once the water has cooled.

What Is a DIY Aquarium Fan? (With Video Instructions)

A DIY aquarium fan is usually a small low-voltage computer fan mounted above the tank.

Building one means wiring an electrical device that sits right next to open water, so it is not a beginner project. A ready-made low-voltage fan is the safer choice. Zoo Med describes its Aqua Cool fan as low voltage (12 V) for safety near a wet environment.

The video below shows one hobbyist’s build. It has not been checked for electrical safety, so treat it as an illustration only:

What Is an Aquarium Chiller?

An aquarium chiller is not technically a fan but is related.

A chiller cools down your aquarium water. It does this by drawing heat from the water and dissipating it into the surrounding environment.

Water is pumped out of the tank, through the chiller where it is cooled, and back into the tank.

You can think of it as a type of refrigeration system.

You use an aquarium chiller because hot temperatures in your tank can adversely affect fish and plants.

What Does an Aquarium Fan Do?

An aquarium fan serves several important purposes.

First, it lowers the water temperature by a few degrees through evaporation. That works for freshwater and saltwater tanks alike. Bulk Reef Supply calls a chiller the most effective way to chill an aquarium, so a fan suits a tank that only needs a small drop.

Second, cooler water can hold more oxygen. The USGS notes that cold water can hold more dissolved oxygen than warm water.

The trade-off is faster evaporation. Bulk Reef Supply warns that a fan causes a much higher rate of evaporation, so expect to top off the tank more often.

What Does an Aquarium Fan Not Do?

It’s just as important to know what an aquarium fan doesn’t do.

First, an aquarium fan does not always turn on or off automatically. Some models do, some don’t.

If you want automatic control, look for a fan that works with a thermostat controller.

Second, an aquarium fan does not move or filter the water. It blows air, so it does not replace a filter, a pump or a chiller.

An aquarium fan is simply a cooling device.

How Does an Aquarium Fan Work?

Here is how an aquarium fan functions: You set up an aquarium fan on your tank, plug it into a power source, and turn it on.

The blades push a stream of air across the water surface, which speeds up evaporation. The USGS explains why that cools the water: evaporation removes heat, leading to a net cooling.

Where Do You Put an Aquarium Fan?

Aquarium fans are typically mounted on the side or back of an open-top fish tank.

Place the fan so that air circulation is directed over the surface of the water. This will result in a slow flow of air across the largest surface area possible.

Do not aim the fan directly into the water.

Keep the motor clear of splashes and make sure the fan cannot fall into the tank. Zoo Med says its fan is side-mounted to minimize water splash on the motor and to prevent accidental immersion.

How Many Aquarium Fans Do You Need?

The number of aquarium fans you need is determined by the size of your fish tank.

Go by the maker’s tank-size rating instead of a fan count. The JBL ProTemp Cooler x200 is listed for 80 to 200 liter tanks and the x300 for 90 to 300 liters. Tunze rates its Aquawind twin fan on a 500 liter (132 US gallon) aquarium.

How To Use an Aquarium Fan (6 Good Tips)

Aquarium fans are simple to use, provided you follow a few guidelines:

1. Top off the tank more often. A fan speeds up evaporation, and on a saltwater tank Bulk Reef Supply says to top off with fresh water, ideally purified RO/DI water.
2. Plug the fan into a GFCI-protected outlet and keep plugs and power strips where water cannot drip on them. The U.S. Consumer Product Safety Commission describes a GFCI as a device that protects against severe electrical shocks.
3. Use a thermostat controller if your fan supports one, so the fan runs only when the water is above the temperature you set.
4. Attach the fan onto the side of your fish tank with a clip or a suction cup.
5. Use a mesh lid with holes or lower the water level when using a fan (fish might accidentally jump into the fan).
6. You should also make sure your fans are clean and dust-free before every use to keep them running smoothly. Unplug the fan first, then use a can of compressed air.

Should I Get an Aquarium Fan?

An aquarium fan is worth considering if your tank, freshwater or saltwater, runs a few degrees too warm.

It lowers the temperature slightly, and cooler water holds more oxygen. If the tank needs a bigger drop than a fan can give, a chiller is the stronger option.

You can get a model that fits the size and shape of your fish tank.

Do Aquarium Fans Really Work?

Yes, within limits. Makers rate them for a drop of a few degrees: Tunze lists 1.8 to 3.6°F for the Aquawind twin fan, and the JBL ProTemp Cooler is listed as lowering water temperature by 2 to 4°C.

A fan is not essential for every tank. A tank that already stays in the right range for its fish does not need one.

How Much Does an Aquarium Fan Cost?

Prices vary by brand and size. As of October 2026, Bulk Reef Supply lists the Tunze Aquawind twin fan at $59.99. Chillers cost more than fans. Check current listings before you buy, because prices change.

Where Can You Find an Aquarium Fan?

Some pet stores carry small aquarium fans, but you will probably find a better selection online.

Here are a few places where you can buy aquarium fans:

• Amazon
• Bulkreefsupply.com
• Petco

Examples of Aquarium Fans

Aquarium fans come in different sizes. These examples have maker specifications that could be checked. They are examples, not test results or rankings.

Final Thoughts: What Is an Aquarium Fan?

An aquarium fan is a simple way to take a few degrees off a warm tank. Watch the water level, top off as needed and keep the electrics dry.

Now that you know about aquarium fans, you might be interested in reading the following posts:

• Are Fans Bad for Fish?
• What Is a Door Fan?

Sources

USGS (dissolved oxygen and water)
USGS (evaporation and the water cycle)
U.S. Consumer Product Safety Commission (GFCI fact sheet)
Zoo Med (Aqua Cool Aquarium Cooling Fan)
Bulk Reef Supply (Tunze Aquawind twin fan 7028.900)
Aquasabi (JBL ProTemp Cooler)
Bulk Reef Supply (cooling your nano)
Bulk Reef Supply (evaporation guide)
National Fish and Wildlife Foundation
FDACS (dissolved oxygen)

Reviewed October 2026. We corrected how an aquarium fan works (it cools by evaporation, by a few degrees), removed fan types and product picks we could not verify, and added guidance on topping off, saltwater salinity and electrical safety near water, using the USGS, the U.S. Consumer Product Safety Commission, Zoo Med, Tunze and JBL product information and Bulk Reef Supply.