How to Choose an Aquarium Chiller

How to Choose an Aquarium Chiller

The ideal range for most reef aquariums is between 75 and 78 degrees Fahrenheit. Fish are more tolerant than corals to changes in the water temperature. However, keeping a consistent temperature is still important. The perfect water temperature for most saltwater fish-only tanks is 75-82 degrees.

Heaters prevent the temperature of the aquarium from falling below the ideal range. However, what if your water temperature needs to be reduced instead of increased? That’s where a chiller can make a large difference in your aquarium. This article will give you an in-depth understanding of whether or not a chiller makes sense for your aquarium and how to choose the proper one for your needs.

What is an Aquarium Chiller?

An aquarium chiller is a piece of equipment used to lower the aquarium water temperature. Water is pumped through the chiller, removing heat from the system before returning it to the aquarium.

1/10 HP Chiller Image Courtesy of AquaEuro Systems
1/10 HP Chiller Image Courtesy of AquaEuro Systems
1/2 HP Chiller Image Courtesy of AquaEuro Systems
1/2 HP Chiller Image Courtesy of AquaEuro Systems

Why Do You Need an Aquarium Chiller?

A constant temperature is ideal for keeping a successful reef aquarium. A chiller will help stabilize the tank’s temperature and prevent water from getting above a specific level by actively cooling it.

How Do They Work?

While it is simple to understand why you would use a chiller, understanding how they work is not quite as easy. The following illustration shows how the chilling process works for most aquarium chillers. However, there are other methods for performing this action.

Aquarium Chiller Illustration
Aquarium Chiller Illustration
  1. Aquarium water is pumped into the heat exchange and flows around metal coils filled with refrigerant (i.e., the coolant).
  2. The refrigerant absorbs heat from the aquarium water. 
  3. The warmed refrigerant is sent to a compressor, where the excess heat is removed using a fan.
  4. The cooled water is then returned to the tank.

Types of Aquarium Chillers

There are three varieties of aquarium chillers.

Inline Aquarium Chiller

This type is the most common aquarium chiller on the market. In this form, water is pumped into the chiller, cooled, and returned to the system.

Ice Probe Aquarium Chiller

A cold probe is placed into the tank water, where it actively cools the water. This is similar to placing a frozen water bottle in the tank. This style of chiller generally works best for smaller aquariums. Installation requires drilling the sump to install a bulkhead where the ice probe is inserted.

Submersible Coil Aquarium Chiller

A chilled coil is placed in the aquarium’s sump for a submersible coil chiller, where it cools the water. No plumbing is required; however, it is not as efficient at cooling the water as an inline chiller.

Choosing the Proper Unit (Sizing)

Like most aquarium accessories, chillers are available in different sizes. Here are the most important factors influencing the appropriate chiller size:

  1. Total Water Volume: The more water, the larger the chiller.
  2. Difference Between Current and Desired Temperature: The larger the differential, the larger the chiller.

Most chillers are rated by their horsepower. And the amount of horsepower correlates with a specific BTU (British Thermal Unit) rating. A BTU refers to the amount of energy needed to decrease the temperature of a pound of water by 1 degree. The higher the BTU rating, the stronger the chiller.

Here’s how to calculate the specific amount of BTUs you’ll need for your system.

BTU Formula

Water Volume x Amount of Desired Cooling in Degrees Fahrenheit x Weight of 1 Gallon of Saltwater (approximately 8.5). For example, if you have a 40-gallon tank and want to reduce your tank temperature by five degrees, the math would look like this:

40 x 5 x 8.5 = 1700 BTU

This would mean that you would want to search for a chiller capable of producing at least 1700 BTU.

Sizing Chart

HorsepowerBTU (British Thermal Unit)Tank Size for a Five Degree Reduction
1/15 Horsepower800 BTUUp to 20 Gallons
1/10 Horsepower1,200 BTUUp to 30 Gallons
1/5 Horsepower2,400 BTUUp to 55 Gallons
1/4 Horsepower3,000 BTUUp to 70 Gallons
1/2 Horsepower6,000 BTUUp to 140 Gallons
1 Horsepower12,000 BTUUp to 280 Gallons
Chiller Sizing Chart

Drawbacks of Running a Chiller

While chillers can make a great addition to a reef aquarium, they also have drawbacks.

  1. Energy Consumption: Most chillers consume a lot of power and lack efficiency.
  2. Physical Size: Most chillers are heavy and bulky, making it difficult to find a place to position them without being an eyesore.
  3. Noise: Chiller compressors are generally pretty noisy, and unlike a refrigerator, aquarium chillers lack insulation to reduce the noise.

Alternatives to Chillers

Even though chillers can reduce your aquarium water to an ideal temperature, there are other ways to accomplish this without using a chiller.

  1. Remove Tank Covers: Removing an aquarium top or tank cover and opening any canopy will increase cooling by allowing evaporation. This will also increase the top-off water needed to replenish the evaporated water.
  2. Fan Cooling: Increase evaporation cooling by blowing a fan directly over the water surface. This will increase the top-off water needed to replenish the evaporated water. 
  3. Frozen Water Bottle: Place a frozen water bottle in the sump for a quick, short-term fix.
  4. Air Conditioning: Reduce the air temperature by turning up the air conditioner in the room.


One of the most significant downsides of using a chiller on a reef tank is the cost. Please consult the chart below for a ballpark estimate of how much you should budget. These recommendations are based upon a five-degree or less temperature reduction.

Aquarium SizeSpend Estimate
15-30 Gallons$150 (Ice Probe) to ≈$500 (Inline Chiller)
30-50 Gallons$250 (Ice Probe) to ≈$600 (Inline Chiller)
50-75 Gallons≈$600 (Inline Chiller)
75-125 Gallons≈$750 (Inline Chiller)
125-180 Gallons≈$800 (Inline Chiller)
180 Gallons+$900+ depending on size and model
Chiller Budget Chart

Selecting a chiller can be a daunting process. Still, if you have an idea of the goals you want to achieve within your aquarium, it can give you more guidance on what you may be requiring. If you have any additional questions about chillers, our support team would be happy to assist you.

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