Determining Chiller Size

We cannot overstate the importance of selecting a correctly sized chiller. Undersized chillers won’t correctly cool your process equipment or materials. Oversized chillers will work just fine, but why pay more than you need to? When you select a chiller of the proper size, you can rely on several years of efficient cooling. Use the formula below to determine the chiller size that will most optimally meet your needs.

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The Formula
Regardless of what you are cooling, this formula will determine your needed chiller size. Before jumping in, identify the following variables:

• Incoming water temperature
• Required chilled water temperature
• Flow rate

To illustrate how this formula works, let’s say we need to cool 4 GPM (gallons per minute) from 85 °F to 75 °F. This makes our incoming water temperature 85 °F, the required chilled water temperature 75 °F and the flow rate 4 GPM.

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Step One:  Calculate Temperature Differential (ΔT°F)ΔT°F = Incoming Water Temperature (°F) – Required Chilled Water Temperature.
Example: ΔT°F = 85°F – 75°F = 10°F

Step Two:  Calculate BTU/hr.BTU/hr. = Gallons per hr x 8.33 x ΔT°F
Example: (4 gpm x 60) x 8.33 x 10°F = 19,992 BTU/hr


Step Three:  Calculate tons of cooling capacityTons = BTU/hr. ÷ 12,000
Example:  19,992 BTU/hr. ÷ 12,000 = 1.666 tons


Step Four: Oversize the chiller by 20%Ideal Size in Tons = Tons x 1.2
Example: 1.666 x 1.2 = 1.9992

Most likely, your “Ideal Size in Tons” is not going to come out to an even 1 ton, 5 tons, 20 tons, etc. Round up to determine which chiller size you will need. In this example, our final answer is 1.9992, which means we will need a  2-ton chiller.

We hope this was helpful! Of course, if you have any questions or would like us to size your chiller for you, please give us a call at (866) 826-2993.