EXPANSION VESSEL SIZE CALCULATOR
What size expansion tank do I need for my closed hydronic system?
To determine the appropriate size of bladder type expansion vessel for a closed heating or cooling hydronic system, follow these steps:
Enter the water volume: Determine the amount of water in the system which includes water in the pipes, tanks, coils, etc, typically measured in litres (L)
Enter the higher water temperature in the system
Enter the lower water temperature in the system
Note: the lower temperature for a heating system is usually normal ambient temperature at fill conditions (e.g.10°C) and the higher temperature is the operating supply water temperature for the system (e.g. 80°C). For a chilled water system, the lower temperature is the design chilled water supply temperature (e.g. 6°C) and the higher temperature is ambient temperature (e.g. 35°C). For a dual-temperature hot/chilled system, the lower temperature is the chilled water supply temperature (e.g. 6°C) and and the higher temperature is the heating water design supply temperature (e.g. 80°C).
Enter the glycol content in the system, if applicable. This is usually measured in terms of percentage of the total system volume
Enter the pressure of the water in the system above the tank location, this is measure in meters and converted to kPa value = mH2O value x 9.80
Enter the highest pressure in the system, this is the pressure set point of pressure relief valve at the location of the expansion vessel
Note: for lower pressure systems, usually a PRV with set point of 300kPa is used
Enter safety factor, a minimum margin of 15% is recommended
The calculator will provide the minimum required expansion vessel size required for the system.
