PEX Tubing questions

Your tubing diameter will depend on the length of your runs. If you keep the total length of each run under 250' you should be ok with 1/2". When I built my house I found a site that listed your length of run vs tubing size and followed that. It worked well for me. The oxygen barrier is preferred for in floor heat as opposed to standard plumbing but I don't know why. The best thing that you can do, and our local building inspector won't let you pour concrete without it, is to have the pex under pressure while you are pouring, that way if you have a problem you know it right away. It's a heck of a lot easier to push wet concrete out of the way than to chip around a broken line. I would suggest that you keep a few coupling around on pour day for just in case. My experience has been if you have the back up plan all ready to go, you usually don't need it. For the pressure test, couple all of your runs together and splice a tee in with a pressure gauge and a shut off valve. The sharkbite fittings work well for this because they can be undone without cutting the pex and I have never had one leak in a variety of situations.