I have been working the phone and calling suppliers this morning to get a larger sampling of opinions and this is what I found out.
I called VanGuard Pipe and Fittings and spoke with Ken who told me that the longest loop can be no more than 300' with a 1/2" pipe.
I called Bow and got an answering machine - they never did call back all day.
I called Watts and spoke with Shawn who told me that no home run should be more than 280'
And to get a third opinion called Heat Link and spoke with Rea who told me no run should be more than 250'. I asked Rea why the others said 280' and 300' and he told me that an engineer can asses the install and approve longer runs but without an engineer the runs should be keep to 250' or less.
I asked each man directly about the length of the run before looping (i.e. no more than 10'-20' before looping) and was told there is no restrictions other than the max loop length.
What other points should we consider in this design? Do any of you guys work in an extra bleeder location? I have seen these installs rough'd in where there is couplings used and spoken with other plumbers who swear they should never be used. I would imagine any coupling would make removing the air from the zone a little harder.