Knowing the following data:

  1. The minimum pressure
  2. The maximum pressure
  3. The volume of the fluid in the system
  4. The maximum working temperature of the system
  5. The possible percentage of antifreeze glycol in the system fluid

it’s possible to calculate the required volume of the expansion tank.


  • The calculation is valid in the hypothesis that the initial pressure (hydrostatic pressure) on the expansion tank is not higher than the pre-charge pressure.
  • The minimum operating temperature is set by default at 40 °F.
  • The set pressure for the safety valve, summed to that one due to the possible difference in height, must be lower than the maximum working pressure of the tank.
  • The calculation provides only an indication of the required volume of the tank and must be checked by a qualified and authorized technician.