Getting ready to put my radiant heating system together and plan to use a primary/secondary loop configuration. I will have 6 or so sets of closely spaced tees on the secondary loop and am wondering if using pex for the secondary loop is a reasonable choice. Size is 1.5 inches and at that size, it seems I wouldn't save too much money using black iron (but would save a lot of time and effort) and copper would be much more expensive with lots of sweating....Anyone use an all pex plumbed system? Any concerns with this approach?