I have noticed in various posts the Marathon is the suggested model for a holding tank. Can someone explain to me why? What is the importance of the "larger ports"? Wouldn't a regular run-of-the-mill hot water heater work just as well? The other question is clearance between the operating electric water heater and the holding tank: Right now it appears I have just over 24 inches to place the holding tank next to the existing electric water heater. Looking at the Marathon unit that would give me about an inch clearance between the two. Is this enough clearance? One more thing, what is a "multi-port"? What is the benefit of this versus a regular tank? Just waiting for the contractor to call me back with "adjustments" to his bid before I sign now. Thought it better to start a new post on the holding tank. Thanks again to all who have helped me through this process. I hope the Waterfurnace unit will be the best choice for me.