If you choose an aquarium chiller, you should consider more than the amount of water your aquarium holds. You should also consider what your aquarium’s temperature drop should be and the air temperature around it. Compared to a chiller that has to cool the water by 15-20°F, one that drops the water by 5-8°F uses less power. Furthermore, warmer ambient temperatures (above +/- 75° F) around the chiller will reduce its cooling performance.
We can use a simple calculation or general rule to estimate how much energy will be required to reach the desired temperatures in our tanks using BTU – British Thermal Units. A chiller’s BTU/hr rating indicates how much heat energy it can remove per hour (BTU). Assume the chiller is placed somewhere with reasonably air temperatures around 70°F without additional sources of heat when using this formula.
How to find the BTU/hr rating of your chiller?
Multiply your tank size in gallons by 8.3. (A gallon of water weighs about 8.3 pounds), Then multiply by the number of degrees you need to drop.
(Volume of water x 8.3) x #° temperature drop = proper BTU/hr rating
For example, in a 75-gallon aquarium, a drop of 4° is needed to achieve the proper temperature range of 78°.
622.5 BTU/hr x 4° drop in temperature = a chiller rated for at least 2490 BTU/hr
When calculating the size of the chiller, it is always better to slightly increase it rather than undersize it, as an undersized chiller will run much less efficiently.
Below is a table of sample fixes for Lando aquarium chiller sizes. This is just for example purposes. Of course, sizes and capacities may vary depending on the unit.