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Thread: Advice needed for B-vent for gas hot water heater.

  1. #1
    Join Date
    Apr 2007
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    central NC
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    Advice needed for B-vent for gas hot water heater.

    Iím in the process for insulating above my attached garage and can see evidence of previous water. Not knowing if this is is ongoing or had been fixed (we are not the original owner) I have been checking after every rain event since July when I started this project. After a very heavy windy rain there was a small wet spot below the first elbow under the roof. Looks like water is running down inside the vent pipe and leaking out at the elbow. The stains on the vent pipe show where the water is running out.
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    A roofer suggested replacing the cap on the flue with a different style. He is not very sure what to do and this is his suggestion.
    IMG_1067.jpg

    The plumbing contractors who came to give me estimates for replacing the water heater do not do any work on the flue. Just swap out the heater which I have had done.

    The flashing at the roof is sound and there is no evidence of any leaking there.

    So, any advice is welcome. the roof is much too steep for me to work on. Those days are long gone.

    NOTE: I take photos with iPhone and create the post on my MacBook laptop. I do not use any editing software or any non-apple software and my photos routinely appear willy-nilly once I post them despite appearing normally to me.

  2. #2
    Join Date
    Nov 2021
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    Columbia MO and Howard County MO
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    It could be condensation from the chimney gasses rather than rain. Leak checking with paper is a clever trouble shooting trick. The service man I learned a lot from would say "check the temperature of the flue at the exit during a heating cycle". B vent is designed so the aluminum interior gets hot quick. If the run is too long (to cool) water starts condensing inside the pipe.
    Last edited by Maurice Mcmurry; 01-08-2023 at 1:20 PM.
    Missouri, it's not that bad. Best Regards, Maurice

  3. #3
    Join Date
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    Doesn't look like much of a leak. I'd put a pan up there to catch it, and see if you can see any at times other than a rain but when there is a lot of moisture in the air. A pan may take care of it anyway. It might evaporate before the pan gets enough in it to run over.

  4. #4
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    Modesto, CA, USA
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    That does not look like a proper roof jack to me. I would caulk where the funnel meets the vertical pipe. I think rain runs down the outside of the pipe and drips down below. That is what happened with my woods stove chimmney.
    Bill D.

  5. #5
    Join Date
    Feb 2018
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    Raise the storm collar above the flashing, put a bead of silicone around the pips and push the SC back down into it. You might consider changing out the cap to a Dura-vent “Brider” style. They are probably the best cap in the B-venting biz. If you do these things and still have water it is likely coming from condensation internal to the flue pipe. Taht is not unusual. It becomes a problem when it is continuous during the run cycle of the appliance. All flues go through a “wet time” cycle, meaning that until the flue warms up and begins to draw properly the flue gases stall on the way out, cool, hitting dew point and condenses on the internal pipe. Given the liner on the B-vent is AL and the ph of condensate is about 3 if the problem persists check the condition of the internal pipe.

  6. #6
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    Quote Originally Posted by Bill Dufour View Post
    That does not look like a proper roof jack to me. I would caulk where the funnel meets the vertical pipe. I think rain runs down the outside of the pipe and drips down below. That is what happened with my woods stove chimmney.
    Bill D.
    What Bill said, not the proper roof flashing, the storm collar does little to stop leaks. Buy the proper flashing and put on and you will need to remove the cap, storm collar and slide the new flashing down and install correctly.
    Retired Guy- Central Iowa. , Cloudray Galvo Fiber , WorkBee 1000x750 CNC Router - Mach4 - Windows 10

  7. #7
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    Nov 2021
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    I do not see a problem with the flashing other than the roof might be steeper then it was intended for. I thought it was plastic at first glance. Zoomed in and with my glasses every thing looks good, although we can't peek under the storm collar.
    Missouri, it's not that bad. Best Regards, Maurice

  8. #8
    Join Date
    Feb 2014
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    Lake Gaston, Henrico, NC
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    I try to avoid flashings that use rubber or depend on caulking to keep water out. There are some that have flexible lead, or I guess Zinc these days, and I remember one that has a lead collar that a clamp goes around, but I don't remember the names. I remember they were something like Luxury Metals, and one with the same letter as high end Mercedes cars, I think AMG or something close to that which has a lead or zinc flexible bellows around the bottom to do some adjusting for roof slope.

    If I did that swap, I'd rent a lift the will get up there. The towable lifts are getting more popular with rental companies. I've rented one for several different jobs, and they aren't hard to tow or use.

  9. #9
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    I have checked it numerous time while the heater was running and did not see any leakage. We had 2 days in single digit temperatures and I would have expected condensation then if it was going to happen. But even when there is condenasation, it shouldn't be running out of a joint. I saw it leaking during the windy hard rain. It was definitely seeping out of the vertical pipe onto the outside of the elbow. This is telling me it is running down the inside of the vertical pipe. The white buildup is on the outside of the elbow.

    So my thoughts are 2 possibilities. The cap at the top of the pipe isn't keeping rain out when it is a windy driven rain. The joint at the elbow to vertical is not as tight as it should be.

    So I need to find a contractor to repair / replace the questionable cap and/or the vertical elbow junction. I suspect it is going to be too small of a job for many contractors to want to bother with.

    I know it is not much of a leak but I want to have it fixed and not be worrying about water infiltration and the problems that can cause over time.

    Thanks for all the suggestions and comments.

  10. #10
    Quote Originally Posted by Bill Dufour View Post
    I would caulk where the funnel meets the vertical pipe.
    Bill D.
    Not on my jobs, would this happen. Flue pipe needs to be allowed to travel thru roof jack when roof rises and falls due to wind. Raise storm collar about 1/2" above roof jack, and caulk it on top side. As Tom said, put a tray under elbow to catch condensation.
    Last edited by Jim Becker; 01-09-2023 at 8:40 AM. Reason: fixed quote tagging

  11. #11
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    Every plumber I've ever asked if they had a bucket under a trap at home said they did.

    I have one air handler in a tight attic that has a condensate trap clog up once every Summer. My fix for that is to put a union in the drain line so I can go up there, disconnect the Union and use a little shop vac that I leave up there to suck the water out of the drain pan, and suck out the lines. I take the top off the little shop vac and by next Summer all the water has evaporated out of it so it will be empty for the next time. I have one of the replacement traps up there that has the caps for putting trap cleaner in, but it's in such a tight spot that so far I'm just putting off changing it.

    Evaporation can be your friend.

  12. #12
    Join Date
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    Quote Originally Posted by Bruce Wrenn View Post
    Not on my jobs, would this happen. Flue pipe needs to be allowed to travel thru roof jack when roof rises and falls due to wind. Raise storm collar about 1/2" above roof jack, and caulk it on top side. As Tom said, put a tray under elbow to catch condensation.
    That is exactly what I meant little funnel thing= storm collar.
    Bill D

  13. #13
    Join Date
    Apr 2007
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    central NC
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    So, to follow up. I found a contractor to replace the cap with a design that is supposed to keep rain out. Also i made a shelf to hold a bucket under the elbow. Belt and suspenders.
    Thanks for all the suggestions. SMC has always been a great source of those with experience willing to advise.

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