Knowing the following data:


  1. The total system volume (gal)
  2. The maximum working temperature of the system (°F)
  3. The possible percentage of antifreeze glycol in the system
  4. The pre-charge pressure (psi) (equal to the minimum operating pressure)
  5. The set pressure for the safety valve (psi)
  6. The difference in level (ft)

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 difference in height (ft) is the difference between the position in which the safety valve  is installed and the position of the tank. Enter a positive difference if the valve is located higher than the tank, negative otherwise (default is 0).
  • 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.