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RobG Member Posts: 1,850
A question about CPVC venting. Although CPVC has a higher temp rating than PVC (and PVC is suspected of leaching chlorides and damaging stainless steel heat exchangers) CPVC stands for chlorinated polyvinyl chloride. This would infer that CPVC contains MORE chlorides than PVC. Combining moisture and heat through either of these materials is bound to create some leaching/ off-gassing of chlorides, especially given the fact that the condensate is designed to drain back to the boiler. So, having less chlorides, wouldn't PVC make a better (less damaging) venting material? (granting that it manufactures approved). 

Just a thought,



  • SpeyFitter
    SpeyFitter Member Posts: 422

    Just use PolyPropylene. It's around the same price as CPVC, higher temp rating than CPVC, and no issues with leeching chlorides.
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • RobG
    RobG Member Posts: 1,850
    Point being

    That's my point! I started this thread so as not to hijack the "Three year old Navian replacement thread". Many manufactures, including Navian, spec PVC or CPVC. Inspectors in my area would fail an inspection if you did NOT use the manufacturers specified venting material. However, what I am wondering is what is worse in terms of chlorides, PVC (as it has less chlorides but a lower temp rating) or CPVC (which has higher chlorides but a higher temp rating)?

  • ced48
    ced48 Member Posts: 469
    How About Running the First

    10 feet in PP, finishing with PVC?
  • heatpro02920
    heatpro02920 Member Posts: 991
    edited May 2013
    I use PVC

    I have seen PP joints fail under ground multiple times...

    I went to a Roth seminar a while back {for their radiant products, nice stuff I like their subfloor system with the alloy and foam, when they were based in N Kingstown, RI, long time ago} and they had a gentleman speaking about a new kind of tubing they were going to be producing, it was interesting and was specifically for 90+ venting, It was made out of polypropylene, but the joint was the interesting part, after cementing the joint you drilled a 1/4" {I think it was 1/4} hole through the joint all the way through to the other side, then you tapped in a couple plastic dowels that you covered in cement... So it couldn't come apart, another interested part about the stuff was the fittings had a tongue and groove rail that was used to hang it with all kinds of hangers they were producing...

    But anyway, I have never heard anymore about it, so I dont know if it was a go or no go, but I asked the Roth rep a while after the class and he said they had trouble with UV exposure, the tubing would break down after it was in the sun too long...

    B ut for now, I just keep it simple with pressure PVC, if your that worried about the condensate that rolls back into the unit being corrosive how about putting a tee before the unit and draining the liquid directly to the pump or drain? {with a trap of course..}
  • Henry
    Henry Member Posts: 998

    You are required to use the venting system that is specified in the certified I&O manual. CPVC has nearly twice the expansion of PVC. If in the US, solid core ABS is better as it only deforms at 217F and it expands at less than 1/4 of cpvc! PP is the Cadillac of condensing vents below 500,000 BTU.

    Don't worry about the chlorides, if the install is done according to the certified I & O manual! It has been tested and certified to work.  
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