All those tee fittings will increase the required head significantly through friction losses. I don't have a Crane or Cameron book that includes PEX but I would use 1.38 or so for the K value of each tee fitting. You also run the risk of short-circuiting your heat transfer if for some reason there is a flow obstruction or something to absorb more heat on one side of the room than the other (such as a rug covering the middle).
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