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PVC v. CPVC v. SS

Kestrel
Kestrel Member Posts: 102
I'm installing my new Lochinvar WHN-085 (pics to come) and I'm getting ready to do the vent and air supply.

My question - is there any advantage between the allowable materials for the air and vent?

It's a wall mount on an outside wall, and so the length of the runs will be in the 2-3 feet range - very short.  Just up, turn 90', turn 45', and out.  I was planning to use the attachment that came with the boiler for placement on the outside wall - a 2-piece oval plastic part that causes the air to pull in from the side and the exhaust to vent directly away from the building.



Any thoughts?

Comments

  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Check with local codes

    Main factor is cost. Stainless is usually the priciest. And as for pvc or cpvc, your local building codes may come into play. Usually codes defer to manufacture guidelines, but some jurisdictions prefer cpvc over pvc, or vice versa.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    runs will be in the 2-3 feet range

    Since I am not a professional, I do not know the venting requirements for Lochinvar boilers. But I have read that some mod-cons have a minimum as well as the usual maximum length for the air intake and exhaust venting pipes. Be sure 2-3 feet is not too short for your boiler.



    Probably has to do with undesired resonances in the pipe.
  • NYplumber
    NYplumber Member Posts: 503
    edited December 2011
    temp

    There is MUCH discussion on this topic.... But first, what is the max temp this boiler will run?

    Start HERE.

    Note, not all pvc is created equal. Foam core pvc can not be used.
    :NYplumber:
  • Steamhead
    Steamhead Member Posts: 14,831
    edited December 2011
    I'd go with Stainless

    not only will it handle higher temps if something goes wrong with the Lochinvar, but it is listed for use in venting combustion products.



    PVC and CPVC are NOT listed for this use. Sure, they're used frequently, but you're on your own if the worst happens.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669
    PVC

    I would use the PVC piping. I install these boilers ( WHN 155 + WHN 285 )

    Keep in mind there is a minimum vent length also. This can be very important also.

    NEVER use a concentric vent termination on a modulating boiler or furnace.( I don't care that it came with the boiler - throw it away) At minimum firing rate in cold weather the exhaust gasses can and will get sucked back into the intake. This is called exhaust gas reversion and is VERY bad for the boiler. The exhaust gasses will cause much higher acid concentration in the condensate. This can eat up the stainless steel heat exchanger. It will also eat into the plastic and aluminum parts inside the boiler. The electronics will not like the acidity and moisture either.

    You need to keep the intake at least 18 inches lower than the exhaust pipe.
  • SpeyFitter
    SpeyFitter Member Posts: 422
    Temp Rating, Quality

    I am not a big fan of PVC of CPVC. A few reasons why

    1) Not as high of a temp rating as other products out there. PVC is 149 F if I'm not mistaken, CPVC is 194 F.  Unless the boiler is only doing low temp radiant heating or snow melt all it's life, you can rule out PVC just about all of the time as far as being the right exhaust vent material due to it's lower temperature rating. CPVC, when you factor in flue gas temps at higher firing rates if you're pushing 170-180 degree water will have it's boundaries pushed potentially, especially in a heat exchanger that needs love/maintenance which may send more heat out the flue than neccessary.

    2) The environmental factor - CPVC and PVC are called the Poison plastic for a reason - these plastics apparently carry some metal for stabilization - do some searches on google for more info.  They generally aren't known to be as easy to recycle as other plastics as well.

    3) On certain heat exchanger designs, some have raised the issue of the potential for chlorides to leech out of PVC and CPVC and drain back onto the heat exchanger through the condensate. Stainless steel and chlorides do NOT mix well and will cause premature failure of some grades of stainless steel. Of course CPVC and PVC manufacturers of their certified vent materials will tell you their products are inert, but I've heard some suggest otherwise as well. Enough to create doubt in my mind.



    For the reasons outlined above I would prefer Polypropylene plastic (if I was using plastics) which does not carry metal stabilziers as far as I know, is one of the most chemically resistant plastics available to deal with flue gas, hydrocarbons, etc., has a higher temperature rating (230 or 248 F depending on which standard you are certifiying it to) than PVC, or CPVC, is very recyclable and more environmentally friendly, about the same price as CPVC roughly, will not leech chlorides back onto a heat exchanger, the list goes on. Stainless steel is another option as well with an even higher temperature rating than PP obviously, being metal, but costs noticeably more, but still a noteworthy option and sometimes it is specified on a job by engineers for particular reasons.
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • Kestrel
    Kestrel Member Posts: 102
    Seems like stainless...

    is the most foolproof.  However, using stainless, from what I'm reading in the installation manual, requires changing out the factory exhaust, which runs from the base of the heat exchanger, out the top of the unit, and replacing it with one of the approved vent manufacturer's replacement adapters.  I'm not sure I'm prepared to do that.



    So if I go with PVC, or more likely CPVC, given the higher temp tolerances, or polypro, if it meets code here (Seattle) - and the polypropylene sounds great, from both an environmental and performance point of view - I still have to terminate it.

    On page 14, Fig 3-2 of the I-O manual, it shows essentially what I want to do - just up and out of the boiler and through the wall.  I can't find mention of a minimum vent length anywhere in the manual, but given that the vent will have at least 1 90' and 1 45' turn, my equivalent length will be at least 8', plus the straight lengths of about 2-3'.



    NOTE - in rereading the manual just now, came across this, which I had missed:

    For Models 55, 85, and 110 using 2" venting and Model 285 using 3" venting, the first seven (7) equivalent feet of vent must be CPVC (field supplied). This includes any transition piece used to increase or decrease the vent diameter.    See examples below.

    So I guess that settles it - thanks everybody for the expert advice - really appreciate it!
  • SWEI
    SWEI Member Posts: 7,356
    plastics

    PVC and CPVC both contain chlorine, with CPVC having more of it than PVC does.  Chlorine is very hard on living things.  Both are difficult to dispose of or recycle.  Polypropylene is an unadulterated hydrocarbon (comprised only of carbon, hydrogen, and oxygen) which is less toxic and relatively easy to recycle.  It also has the aforementioned higher melting point.



    Last time I checked, polypropylene vent pipe was priced somewhat lower than schedule 80 CPVC pipe of equivalent size.  I did not price fittings.
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