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Tidbit # 6; Slipping Vent Pipes

Here's a heads up for you service persons:

I (we) have been running across WAY TOO MANY leaky, burnt, or disconnected exhaust vent connections! Anytime you are around a Mod-Con with the rear no-hub looking exhaust connector, check it for leaks and verify it has not loosened! I have been safety-strapping the PVC just to make sure it won't slip out. Had to replace the connector on a few, and it ain't real easy. Any condensate drippage is a leak indicator.


  • icesailor
    icesailor Member Posts: 7,265
    Slipping Connectors:

    If the connector is a No-Hub coupling, it should last. That's a coupling with the stainless steel shell. If it is a "Fernco" type rubber sleeve with two stainless steel clamps, Fernco's are bad news on the long haul. I have seen them used to repair broken cast iron soil pipe in walls and after three years, the rubber is rotten and split. I only use No-Hub clamps. Where I work, there was a major sewer replacement three years ago and the contractor used 6" PVC SDR pipe to connect to whatever pipes came out of the houses. Usually 5" VC or 4" Cast Iron. They used a 6" Fernco coupling on the PVC and and whatever would connect to the old pipe. They also used a 6" double TY so you could rod in either direction at the property line where they ran a clean-out cap to just under the sidewalk. I have had three blocked sewers this summer where the roots went right through the Fernco between the rubber and the pipe. Years ago, I had one where the roots went through and broke the clamp as the foot became the size of my thumb.

    Don't trust Fernco's. They rot and leak.

    In my experience.
  • Charles Johnson
    Charles Johnson Member Posts: 24
    Good reminder

    I had a 400 Mbtu mod con blow the PVC piping off due to delayed ignition.

    The Lofgren CO tragedy was due to PVC flue piping coming apart I believe.
  • Bob Harper
    Bob Harper Member Posts: 1,030
    Fernco's for venting?

    I spoke with a product engineer at Fernco about applying them for combustion venting such as with Sch 40 PVC joints. He replied they do not condone, approve or market their product that way. When I asked him about those reducing couplings provided by Bradford White on their TTW power vented water heaters he confessed they are the supplier for those components. He said its was up to the mfr. what they did with Fernco's components. I said if there was a loss Fernco would be included in the suite. He assured me they have never been named in a suite for the water heater application but hedged on the issue about applications involving other heating appliances. He did say their couplings are rated 140F continuous and about 165F for very short periods once in awhile but not sustained. Again, they don't test their product venting combustion gases. He said they do test against acids and alkalis because such products can be expected in DWV drain pipe for ex. but not flue gas condensation. Basically, he was saying if you want to use his products on CAT IV gas appliance venting, the liability transfers to the seller of the end product, their distribution channel, retailers and installers & service personell.

    This gets back to the old debate of whether or not to use glued PVC. This product category is unlisted for combustion venting in the US so you're on your own with this material.
  • Bob Harper
    Bob Harper Member Posts: 1,030
    follow up on myself-sorry

    As to proper installation of glued PVC, understand there are a number of issues. Aside from the uneven expansion during heating such as the hoop stress on the hubs and cement, there is elongation, too. Properties of materials change at different temperatures. Since there isn't much test data on this application, there cannot be a solid recommendation for its use as a combustion vent. We do have some anecdotal evidence along with litigation to indicate there have been failures but there is no clearinghouse to put together a clear picture. For instance, what if all the failures were due to an appliance being grossly overfired such as LP fired into a unit set up for NG?

    If you secure PVC too well, you can cause problems as well. If you must penetrate framing members, walls, etc. be sure to bore a hole well in excess of the pipe's OD. Allow for longitudinal was well as vertical movement to a degree, while still supporting horizontal runs every 4ft. and promimate to each joint and offset. PVC is rated as a combustible so maintain stated clearances to combustibles. There is no listed firestop assembly for Sch 40 PVC as a combustion vent so it should never be used vertically over 3 stories, which would require fire rated assemblies.
  • Xavier Breath
    Xavier Breath Member Posts: 19
    Hilti will supply you with an engineered judgement

    We've received approval of a fire-stop system once Hilti's engineered judgement was included in our submittal.


    Not sure how sched 40 PVC will be received, however. 

    FYI: In MA, by code, the venting of all boilers & other combustion equipment is now the plumbers work (up to a certain btuh). 
    You are what you know
  • icesailor
    icesailor Member Posts: 7,265
    MA Code/Venting

    I think what the Massachusetts code says is that the person who takes out the gas permit is responsible for the venting. In Massachusetts, licensed plumbers are also gas fitters. Although they also have a separate gas license and gas fitters are not plumbers, There were many cases where a "heater" installed a heater and did the venting. A gas fitter or plumber did the gas. The venting was wrong. Who was responsible.

    Then, there is venting oil equipment. It was back and forth. The final word was that maybe you need a sheet metal license to vent an oil appliance.

    Its a real ship show.
This discussion has been closed.