Issue: 10/03

How do you size expansion tanks for larger closed-loop radiant heating systems? Chances are you use the same methods you would for other hydronic systems. The classic sizing procedure for a diaphragm-type expansion tank compares the volume of the system's fluid when the system is at it highest temperature to the fluid volume when the system is first filled. An expansion tank volume is then calculated to accept the increased volume without allowing the system pressure to climb high enough to open the relief valve.