Expancian Tank Home › Forums › Public Forums › General Plumbing › Expancian Tank This topic has 1 reply, 2 voices, and was last updated 23 years, 3 months ago by Guest. Viewing 1 reply thread Author Posts 25 Jan 2001 at 3:50 pm #274494 MasterPlumbersKeymaster Can some smart plumber please tell ma how to size a expancian tank for my well (the formula if there is one) PLEASE PLEASE I am having trouble getting this info and would realy appreciate a handThanxBrandy 26 Jan 2001 at 1:41 am #289847 GuestParticipant you didnt say what you use the well for somewhere out there in agri-farmer state university it is written… minimum of 1-gal per 100 GPH flow capacity, which hopefully be limiting the cycles to under 25 per hour. Author Posts Viewing 1 reply thread You must be logged in to reply to this topic. Log In Username: Password: Keep me signed in Log In