I'm about to plumb in the hot water heater and checked with my coop. They have backflow at the meter so I'm closed loop. Therefore I'm going to put in an expansion tank. It's a small 18" diameter electric 30 gallon in a TIGHT space so I don't have a lot of room to play. I have seen the following mount in several pictures and I'm assuming this is "OK". I'd use sweated copper to a T that joins the outgoing hot line via PEX that terminates at a 3/4 connector coming out of the wall. Obviously I would connect flex pipe like in the pic. The copper, I assume, would give enough strength for the smaller (2 gal) tank.
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