I was reading another thread about sizing of expansion tanks and there was a link there to an Amtrol calculator. According to it I would need a AX-144. Since my system is basically the same as others, 1,000 gallons storage, and some say that the AX-144 isn't big enough by its self I may need more. OK price out a AX-144 ~$3,000!! Yikes I am wondering why can't I just route a piece of pex from the top of my storage to the attic and have that terminate in the bottom of and tub? Is it concern of oxygen entering the system?