I am running Double - 3/4" PEX-AL PEX lines to the BARN. The ID of the 3/4" PEX-AL PEX lines is .807 (each) so the water carrying capacity of the double line is far in excess of my current needs. I am building with expansion in mind. I think we'll use spray foam insulation. The distance outside is roughly 200 ft (one way) but I'll have to go about 80 feet through the house. It's a long run. By the way, I chose Doubling the 3/4" Pex-AL Pex rather than 1.25" PEX because of a good sale price. Because my heat load is very low (10-11000 BTUs), due to some straw bale insulation, the flow doesn't have to be huge and therefore the head is manageable. Inside the barn, I plan to run pex piping along one wall in each of 2 rooms in a staple-up configuration. I am planning on using reflective bubble barrier behind the pex. What I need help with is this - What is the minimal size pex that I can get away with in the individual MushRooms ? Do I need another circ in the barn? Should I have a manifold in each room and run loops off the manifold or can I just loop back and forth in in one continuous loop in each room. The rooms measure 40'X12' and 16'X28'. The long wall in each room would support the staple up pex.