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Flexible PVC pipe was used for venting a High Efficiency Gas Furnace - Water spot in base of Chimne

J1234
J1234 Member Posts: 8
edited April 2021 in Gas Heating
What is needed to fix this problem? When the High Efficiency Gas Furnace is running, a water spot forms at the base of the Flue chimney where the Flexible PVC pipe, enters the chimney and then vents to the roof. There is NO liner in the chimney. The furnace has two pipes entering the chimney, one for the inflow and one for the exhaust. Rigid PVC pipes were used to exit the furnace and connected to flexible black PVC (schedule 40) pipes, using purple glue. The flexible PVC pipe goes into the chimney then is connected to the rigid PVC pipes, at the top (picture below), both using purple glue. The contractor used terminates, consistent with a wall install. What could the water spot be? How do I test it? Can flexible PVC pipe (schedule 40) be used in this application? Is there a need for a stainless steel liner?

Comments

  • J1234
    J1234 Member Posts: 8
    edited April 2021
    These are the terminates:

  • J1234
    J1234 Member Posts: 8
    This is the wet spot, which grows when the furnace runs more in the colder months. The flexible pipe is supposedly to be flexible PVC. Is this flexible PVC, schedule 40?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,203
    Without more information, it is difficult to know exactly what you have. In the first photo, the exhaust should be the pipe ending on a verticle plane (shooting to the right) The intake should be the pipe that is pointing down. on the left As the other chimney vents combustion exhaust, there is a possibility that those combustion gasses will enter the intake. What is the other chimney used for? (a wood fireplace?) The PVC exhaust pipe should be the rigid type for the complete path. The flexible can be used for the air intake.

    This water stain may be an exhaust leak in the vent pipe. It could also be condensation forming on the exterior of the vent pipe. The corrugated flexible pipe is not approved for furnace venting. it is most likely for drainage only. I would look for an alternative side wall location using the installation manual for the appliance that you are venting. There will be illustrations of where that can happen.

    Mr.Ed
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
    J1234
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,019
    Could be an unrelated flashing leak around the PVC on top of the chimney. I would check that first
    J1234
  • Zman
    Zman Member Posts: 7,332
    What make and model is the furnace?
    Flexible PVC is not schedule 40. It is nowhere near as durable and has much higher resistance.
    I have never seen it allowed in an installation manual and would be very concerned if this was my house.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    HomerJSmithJ1234
  • HomerJSmith
    HomerJSmith Member Posts: 1,567
    It appears to me to be stainless steel corrugated chimney pipe . You can see the weld heat discoloration. So the flexible PVC goes into the stainless pipe and up the chimney. The problem is that the manufacture gives you the specification of the PVC pipe you are suppose to use.

    If you have a leak on the flue pipe water laden exhaust gasses could condensate in the cold masonry chimney and drip down, making the wet spot.

    You would probably get smoke into the furnace intake pipe if the furnace is working at the same time as the fireplace is working. But smoke won't get into the house, just into the combustion chamber of the furnace, not good, depending on which way the wind is blowing. The half round pipe on the roof is the furnace air intake.
    J1234
  • J1234
    J1234 Member Posts: 8
    BTW, the township failed the HVAC system for the terminates and the wet spot.

    The Make and Model of the furnace is Rheem, R96VA0852521MSB. The Rheem training expert said that there should be a chimney liner put in prior to the pipes being run up the chimney. But when I called to order the chimney liner, the Rheem distributor said that they do not sell the liners and the vent piping should never be put up a chimney (and added that there was a civil suit, years ago, etc. - can't find the civil suit information).

    *Chimney specialists inspected the flashing and chimney and said that chimney and flashing is Not leaking and the leak is coming from the pipes.

    The pipes are rigid PVC to flexible PVC (supposedly all Schedule 40).

    Does anyone have the specs for flexible PVC (schedule 40) and a reason to not use these pipes? Anyone aware of a civil suit that indicates the vent piping from a furnace should not be run up a chimney or that flexible PVC (schedule 40) pipe should not be used for this application?

    Thank you for all the information. I am so grateful for your help.
  • Zman
    Zman Member Posts: 7,332
    I searched long and hard a few years ago for any standards for flex PCV. I was looking into failures in hot tub piping. If you find anything, please post it, best of luck. ;)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • J1234
    J1234 Member Posts: 8
    edited May 2021
    Does anyone know the temperature of the exhaust going out of the house from a high efficiency furnace?

    Flexible PVC pipe shrinks over time, especially when exposed to heat and is a soft material.

    The flexible PVC pipe is rated for temperature up to 130 degrees.

    Web site:
    What our Flexible PVC Pipe is NOT intended for:

    High heat situations. Our Flex PVC Pipe is great for many applications, but it is too soft to work well in situations where you are venting hot air, such as furnaces, water heaters, wood burning heaters, etc. Do not use our pipe in these situations because the high heat could cause the pipe to collapse, potentially causing a hazardous situation.
    Chemicals. While our Flex PVC Pipe works well with many chemicals (i.e. swimming pool and spa applications), it may not work well with all chemicals, especially those that are in their un-diluted state (swimming and spa chemicals are in always used in a “diluted” state).
    Insects. Our Flexible PVC Pipe is not resistant to insects, such as termites. While we do not believe that the product attracts termites, we have had reports where termites have eaten through similar pipe in areas of high infestation and insect activity. If you have a termite or other insect problem, cure the problem before installing the pipe.
    Stacking. Flexible PVC pipe is not intended to be stored in a coiled position in stacks higher than 6 rolls for any extended periods of time; damage may occur.

  • mattmia2
    mattmia2 Member Posts: 5,544
    J1234 said:



    Does anyone have the specs for flexible PVC (schedule 40) and a reason to not use these pipes? Anyone aware of a civil suit that indicates the vent piping from a furnace should not be run up a chimney or that flexible PVC (schedule 40) pipe should not be used for this application?

    Does it have the astm spec number specified in the manual for the vent pipe printed on it? Does the manual qualify it with "rigid" or "solid" or "not cellular"?
  • bob eck
    bob eck Member Posts: 929
    You must have you high efficiency condensing furnace or boiler vented to the manufacturer instructions.
    Hire a professional heating contractor that can install the venting correctly and up to local code.
    As far as I know no manufacturer has approved flexible pvc or any other flexible vent pipe to be run horizontal to the chimney base.
    Hire a professional heating contractor before someone becomes sick or dies from flue gas that leaks into the home.
    J1234
  • Jamie Hall
    Jamie Hall Member Posts: 18,970
    @J1234 asks "Does anyone know the temperature of the exhaust going out of the house from a high efficiency furnace?"

    Depending on the exact conditions that the furnace is operating under, it can be up to 300 F for short periods of time. Steady state can be over 140 F.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    J1234
  • Zman
    Zman Member Posts: 7,332
    Furnaces will run in the 140-degree range, boilers 200ish.
    This is the only flex product I am aware of that would be appropriate for your installation.
    https://www.supplyhouse.com/DuraVent-3PPS-FLEX35-3-x-35-Flex-Length?gclid=Cj0KCQjw24qHBhCnARIsAPbdtlKOJ7FUdOHp270tB3bkf6-FslDULdNcJ7PYgToNkccj8ffU28PAK-AaApC1EALw_wcB
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    J1234
  • J1234
    J1234 Member Posts: 8
    Zman, you are the second HVAC guy to think that the pipe is DuraVent and should not have been used. I have a high efficiency propane furnace.

  • Bob Harper
    Bob Harper Member Posts: 914
    The IRC calls for all venting under positive vent pressure to be listed. That means UL 1738. You can use CPVC flex liners but not PVC, which is only approved for non-potable water plumbing applications.
    The chimney dudes need to go to school. Aside from a small single flue cap that doesn't protect the crown, there is no cast concrete crown with a 2" overhang and 1.5" drip edge with a 10 degree slope for drainage with a through-flashing and resilient seal to the flue tile and weep holes above and below the crown. The stone was pointed with Ordinary Portland Cement-based mortar, which is too hard, retains water and will ruin the stone. It should have been cut to a minimum of 1", rake out all non-viable material, then repoint with a Natural Hydraulic Lime 3.5 mortar. Lime breathes, has a high modulus of elasticity, and is very vapor permeable promoting rapid drying to the atmosphere. The flashing was cosmetically adhered and not properly 'let' into a reglet or 'raggle'. The water stuck in the OPC mortar will be driven inwards by vapor diffusion until it hits a capillary break, typically the gap that's supposed to be btw the chimney proper and the flue tile (1/2"-4" air space). Here, the water vapor will condense. Gravity will draw it down where it can manifest as a "leak" anywhere below.
    Even with a listed flex liner, it should have a thimble or sleeve to protect it from the masonry and not be directly cemented in place.
    I know of only one ss liner listed under 1738 for CAT IV gas.
    If you want to prove that liner is not leaking simply insert a test ball, fill it with water and watch for it leaking. Do NOT use pressurized gas such as air or N2!
    J1234
  • J1234
    J1234 Member Posts: 8
    We scoped the chimney and found that only the exhaust pipe was run up the chimney and it was leaking. The intake pipe terminated at the base of the chimney and there was NO intake pipe run up the chimney to the outside air. All the intake air was being drawn from the flue chimney. The cement eroded at the base of the chimney. Who know what this did to the HVAC system??? The chimney has also deteriorated. :-(
  • J1234
    J1234 Member Posts: 8
    Who should this be reported to because these guys are still out there installing HVAC systems and could kill someone?
  • pecmsg
    pecmsg Member Posts: 2,899
    Generally the authorities having jurisdiction. Here it would be the building department but there not going to do much. 
    Next step is the local, county, state attorney genera. Again they may may not investigate. 
  • pedmec
    pedmec Member Posts: 193
    centrotherm makes a flex polypropylene to line chimneys but has to be installed as part of the centrotherm venting system. it is listed to ul-636 and ul-1738 standards. don't know what crazy stuff you got going on there.