Water leaking and white powder at flue joint
Page 1 of 2 12 LastLast
Results 1 to 13 of 15
  1. #1
    Join Date
    Oct 2006
    Posts
    24

    Water leaking and white powder at flue joint

    Hello. I was looking for some expert advice and suggestions to a problem I noticed down in my basement.

    My HVAC unit has been running well for the past couple of years but I've noticed that my flue pipe that runs out from my unit drips water at one of the joints where two 4" flue pipes meet. The dripping water seems to come only when the furnace is running and seems to stop (or be much less) when the unit is off or at rest.

    I've also noticed right at this joint that there's a white chalky powder or residue that's accumulated at this area. I was wondering what people's thoughts were and if it's a major thing to fix.

    I assume the water is condensation and I'm assuming the white powder is from the chemicals of water mixing with the exhaust gases but I was hoping for some additional thoughts.

    I'm planning to call several new HVAC specialists in my area to have them evaluate and correct (as the ones that put this in are no longer around..I wonder why) but I wanted to be as informed as I could as sometimes I haven't had much luck with honest contractors (as you can tell from the topic here..)

    Any thoughts would be greatly appreciated! Thank you all.

  2. #2
    heaterman's Avatar
    heaterman is offline AOP Committee/Professional Member*
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,841
    Not alot of information to go by but your HVAC company will most likely recommend a flue liner for your chimney if it is of masonry construction. The moisture you see is condensation from the flue gasses cooling in the vent system before they can draft out. This condensation is caustic and will eventually result in damage that will reduce the life span of your equipment.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  3. #3
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Is it a 90%+ furnace? Is the pipe PVC or metal? If it's a condensing furnace (90%+) and/or PVC then the condensation is normal, but the leaking isn't. You are correct about the white powder. If it's a condensing furnace and the insaller didn't use a proper liner... not good.

    IF it's a 80% furnace and there's that much moisture all the time, something doesn;t seem right.

    Either way, the leak should get fixed.

  4. #4
    Join Date
    Oct 2006
    Posts
    24
    Thank you all for your thoughts. And sorry for not being able to give more info or pictures...

    Interesting that you mentioned about the chimney liner as I know the entire chimney is made of wood (square in section) and it's only covered with siding without any insulation.

    I also noticed the top of the chimney was open and not covered. In other words, there is a cap to the flue/chimney but it looks like just a round cylinder in a square frame with no covering to the top of the square frame.

    I imagine between this opening and the fact that the chimney frame itself is only wood/siding, the flue must be too cold itself and therefore the condensation forms.

    The pipe itself is metal and forgive me as I'm not sure if it's 80% or 90%+ furnace. How would I be able to tell?

    Thank you all again for your continued thoughts.

  5. #5
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    Is the metal pipe double or single wall?

    Even double wall pipe isn't supposed to be installed outdoors- which is what you are basically describing with an uninsulated wood framed chase.

    PVC pipe used to vent condensing furnaces is supposed to be insulated when installed in outdoor ambient conditions.

    Your chase should have some type of top to keep water from the interior.

    If there is a long distance from the furnace to the flue connection, and if that is done in single wall pipe, then replacing it with double wall Type B vent pipe will help. Note that the distance should not exceed 1.5x the flue diameter in feet.

    Not sure if there are any UL listed products made to insulate the exterior of Type B venting.

    Insulating the interior of the chase may also help, but that won't be easy. If kraft paper faced insulation is used, then it must be drywalled over.

  6. #6
    Join Date
    Oct 2006
    Posts
    24
    I wanted to help clarify the point I was making above. What is missing up top is a 'top plate'? Here's an image of what looks to be missing.

    So I can imagine that since it's open and exposed, the flue is much colder than desired. By the way, the water dripping is not a whole lot, but I'm sure just having this open contributes to the flue getting that much colder. Thanks again.
    Attached Images Attached Images  

  7. #7
    heaterman's Avatar
    heaterman is offline AOP Committee/Professional Member*
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,841
    Sounds like a type B metal vent chimney in a chase. Most likely oversized, you will need to have an HVAC company take a look.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  8. #8
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    "Up top" where?

    Where the flue enters the chimney chase, or the top of the chase itself?

    The point of entry for the flue at the base of the chase should be firestopped with metal.

    Good point with the oversizing, too.

  9. #9
    Join Date
    Oct 2006
    Posts
    24
    Yes, the top of the chase itself seems to be missing something like the image posted. It's completely opened up top which I can imagine was either never done by the previous contractor or blew off completely somehow.

    And I'm not sure if it's double walled or single walled but I'm hoping it's double walled at least.

    And finally, would you all recommend having a specialist work on it now in the winter or wait til it gets warmer? I just didn't know if there were any problems with shutting the unit down and doing this work now with the winter (we live in NY and it's mighty cold now...)

    Thank you all again.

  10. #10
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    If the top is missing, then there is an entry point for water- liquid or frozen.

    You should not wait.

    The image you posted looks more like a firestop/support used to hold up the vent pipe and provide firestopping between floors. It does not look like a cap or chimney top.

  11. #11
    Join Date
    Oct 2006
    Posts
    24
    Oh I see. I would have imagined that the top of the vent pipe needed something to cover up the opening and I thought that part was the thing that we needed.

    Ok, we won't wait then and give someone a call.

    But would you all know if there are some listings or references where I can find some reputable specialists in our area? (NYC metro/Brooklyn).

    I ask as I've mentioned that we didn't have much luck with previous specialists - as you can see- and wanted someone that's knowledgeable.

    Thanks!

  12. #12
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    There should be a cap on the top of the vent pipe.
    Attached Images Attached Images  

  13. #13
    Join Date
    Oct 2006
    Posts
    24
    Wow, that looks much different than ours. Our vent currently looks something like this:

    Should we get this type replaced as well?
    Attached Images Attached Images  

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event