I found this information from the DOW website:
Quote-
Plastic Piping
There has been a steady increase in the use of plastic tubing over the last 20 years. Polyethylene (PE) or cross-linked polyethylene (PEX) represent the most popular choices in terms of reliability and cost. Other materials such as chlorinated polyvinyl chloride (CPVC) or polyvinyl chloride (PVC) may also be used depending on operating temperatures. Several TES systems using either ethylene glycol- or propylene glycol based heat transfer fluids have operated successfully for years with no detrimental effect on their PVC piping.
However, some PVC/CPVC suppliers recommend that propylene glycol-based fluids only be used in solutions no greater than 25%. In every case, regardless of the plastic being considered or the concentration of glycol desired, it is recommended that you consult the plastics supplier to verify compatibility with ethylene or propylene glycol fluids before installation.
-end quote
Here's the site:
http://www.dow.com/heattrans/fsa/system.htm
Mitch