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How to Size a Water Chiller

The importance of selecting a correctly sized chiller is crucial. An undersized chiller will always be a problem– never able to properly cool the process equipment and the process water temperature will not be stable. An oversized chiller will never be able to run at it’s most efficient level. Identify the correct size chiller and rely on years of continuous, efficient cooling for your application. If you would like help, feel free to give us a call. To give you an idea of how to correctly size and select the best solution for your application, please use the formula below.

water chillers


  1. Calculate the ‘delta T’, the change in temperature, between the inlet and outlet water. Measuring the ‘delta T’ requires a thermocouple or thermometer. Check the water temperature of the water inlet line and the water outlet line, and subtract the numbers to compute how much heat the equipment is adding to the water.
  2. Rate of flow in gallons per minute (GPM). To measure the flow rate of the water place a flow meter on the outlet line of your equipment. If one is not available, simply measure the time it takes for the outlet flow to fill a five gallon bucket, and then compute your gallons per minute (GPM) of flow (see calculator below).
  3. Now that you have these two figures, calculate how many BTU’s (British Thermal Units) your equipment puts off.
BTU/ hour = 500 x GPM x Temperature Difference (delta T)

Repeat this for all the equipment you have, and add up the total BTUs. Now that you have the BTUs, compute the total tons of cooling you need from a chiller. For example, 1 Ton of cooling is 12,000 BTU/hour s

# Tons = (BTU/hr) / (12,000)

This is the size unit you should need. There may be other circumstances, like planning for expansion, high ambient temperatures, etc that could lead you to buy a different size unit. Feel free to contact us to help review your calculations