Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

PVC Venting Mfg Comments

CMadatMe Member Posts: 3,085
This seems to be the hot issue of the year. From columns in the trade mags to the long threads here. This thread is for all trade professionals that have inquired to the mfg of the equipment they use concerning PVC venting and a place for mfgs to respond if they choose with the data on why PVC is a safe means for the removal of flue gases eventhough the mfg of the product itself does not rate or state it. 

Since I'm a Viessmann guy and they have put their stance on PVC venting in writing I'll open the thread.  Please see their statment at:

<a href=""></a>
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."


  • Tim McElwain
    Tim McElwain Member Posts: 4,487
    Thanks Chris

    hopefully others will chime in.

    I wrote two articles back in 2008 on PVC and CPVC venting. My THEORY was that possibly chloride gases were redistributing back into the combustion chamber. I posted this in another posting that JDB started and was challenged for proof or some lab testing to substantiate my THEORY. I had none nor do I yet as I am not a lab nor do I have access to one.

    I did however receive a very nice personal letter from Harold Prell the President of Viessmann. He stated that my THEORY was not a theory but Viessmann had determined that was the case and had put out a letter to the fact in August 2007 which is what Chris attached.
  • CMadatMe
    CMadatMe Member Posts: 3,085
    edited June 2011
    Just Tired

    Of beating a dead horse in threads concerning this issue. We are all professionals. Can't tell you how many posts I have read concerning on-demand hot water heaters being used as primary heat sources and guys comment that they are not rated. What's the difference? The mfg says you can use as a heat source. Trial and error to justify that a product is proper for the applicationis is foolish and to this point that is what PVC has in its bag.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • icesailor
    icesailor Member Posts: 7,265
    PVC Venting:

    And as I have asked/questioned over and over, have the PVC ie and fitting manufacturers said that they would defend you in court if there is a failure and you are held liable.
  • Tim McElwain
    Tim McElwain Member Posts: 4,487
    edited July 2011
    Here is some information from a

    manufacturers rep:

    Hi Tim,


    I felt a need to contact you regarding something that was lacking from all of the replies on Pvc pipe..


    We call for the installer to use the CPVC venting material (30") that we provide to allow for cooling of the flue gasses to the tolerance that the PVC resin manufacturers call for or 140F. We also state that the PVC pipe being used be "SOLID CORE" Schedule 40 and NOT PVC "Cellular or Foam Core" pipe. Several years ago I was in my driveway outfitting one of our rolling display vans with two Alpine boilers that were stacked to demonstrate that capability. I decided to use PVC on one of them and Polypropylene on the other to show the different vent materials. When it came time to pick up some Schedule 40 PVC pipe from a local distributor, I was disturbed to find that very few RI distributors even carry "solid core" pipe anymore. All I contacted only had "Foam Core" in stock. To be politically correct in continuing my search for "Solid Core" pipe I ended up at The Home Depot.


    As Mr. George stated, many contractors prefer to use inexpensive items in an effort to stay competitive for fear of losing a job. The thing that troubles me is that I have been on numerous jobs where "Cellular Core" was used, either due to ignorance to the difference or due to trying to stay competitive. I had many installers remove the pipe and replace it with the correct pipe. We also call for CPVC pipe to be used when the piping is enclosed in a vertical or horizontal chase way as the pipe temperatures can elevate or stack in temperature without the surrounding air to effectively cool it. Mr. George is correct regarding the stance of the Pipe Manufacturers as clarified by the attached memo from Charlotte when we were giving consideration of PVC as a venting material for the Alpine and Freedom boilers.


    As for the jobsites that Mr.George was referencing in his article, he fails to give mention as to what grade of PVC pipe was used in the installations. I would probably think that at least some of them may have been "Foam Core" or even some other grade of PVC such as SDR pipe. I have seen PVC discolor on some jobsites where the pipe is tucked up inside of floor joists or in chase ways where traditional cooling by surrounding air is not present. Most equipment manufacturers use flue gas sensors to aid in protecting the vent system and U.S. Boiler is no different. Our control is set to kick in a Fan Rate Limiter when the flue gas temperature exceeds 192F and will activate a "Hard Lockout" if the temperature exceeds 204F. 

     As for the incidents that do happen out there, we unfortunately have no control over how these boilers and venting are installed. Provided all guidelines and warnings are adhered to, the installation should not encounter any problems. I have been on many installations where chemicals (Pool Treatment and even Miracle Gro) have been in the area of the air intake and virtually disintegrated the swirl plate in the fan shroud. I would also be safe in saying that PVC exposed to chemicals in the surrounding air could also lead to degradation of the PVC as shown in a couple of the photos posted. I'd be interested in knowing what grade of PVC was used in the installations Mr. George was referencing.


  • CMadatMe
    CMadatMe Member Posts: 3,085

    Very interesting point of view. Clearly their use of CPVC before any transition to PVC Sch40 states that they do not want to exceed the 140 temp when using PVC.  
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
This discussion has been closed.