5/8" would have been smarter. And definitely keep loops under 250', and my pex was spaced every 16", 12" would be better. Again, a miscalculation on my part. So in a perfect world, you'd want 7 loops of 250-ish 5/8" pex. But 5 300' loops of 1/2" do work also. I keep the shop around 60 degrees...