macdabs wrote:The 1'' with the right pump should work fine for a 85' length not to mention you can purchase 1'' at almost any local heating supply house ,fittings and crimps our much more common also..
I would be hesitant to recommend a pipe or pump size without knowing what the load is. You can shove about 7 gallons per minute through 1" pex with a big pump, and that may or may not meet his needs. It wouldn't do the job at my house, and even if it would...I would prefer larger pipe and a smaller pump. You buy the pipe once and the electricity every month.
Threaded pipe is tough stuff...if you want to use it, pressure test the lines before backfilling the trench.