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  1. #1
    Join Date
    Nov 2019
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    Question Excessive condensation from furnace vent - vent cap improperly installed?

    The problem: I have what I think is excessive condensation running along the vent pipe into the house.

    The question:
    Should I have a roofer climb up and ensure that the vent caps are properly installed to vent moisture and heat?



    The background:


    I have a garden-variety furnace that vents up through the roof.



    We had a metal roof put on and now that it's cold and I turned the furnace on, I noticed the condensation. The metal tape on the bottom of the pipe is what I used to crudely funnel the water to the AC drip pan.

    Not a huge amount of water, but too much to look normal (to my novice eyes) and more than I want on the OSB in the attic:

    Roof penetration:

    Note the condensation on the inside of the plastic/cloth material - and should that material be cut and tucked neater than it is (is it bad that it might touch the vent pipe)?

    The pipe gets pretty hot when the furnace is on. Not glowing red hot, but definitely hot to the touch. I thought it should be double-wall pipe and it should be warm but not hot?




    My theory:


    The vent cap outside is the wrong type and sitting all the way down on the pipe, so it partially blocks the vent. It vents enough for the furnace to kick on (total blockage and the vent fan in the furnace wouldn't flow enough to turn on the furnace, right?), but maybe blocks enough that the moisture in the exhaust air doesn't entirely vent out but condenses on the vent cap and dribbles back inside the house along the pipe?

    One reason I suspect this is because that is what they did for the 4" vent for the water heater!

    When the water heater was swapped out, the tech said the top of the heater got too warm, climbed up on the roof and saw that the vent cap was a 6" cap on a 4" pipe and sitting all the way down and screwed onto the pipe - effectively mostly blocking the vent.



    I don't recall it dripping previous winters with the old shingle roof, but I also have nothing but curses for the roofers for a host of (other) reasons, so I won't call THEM out to fix this. If the vents are the likely culprits, I'll call another roofer to do the work.

    The big issue is that I can't get up to the 2nd level roof without killing myself (satellite image of my house https://i.imgur.com/QAjeg69.jpg), so if my theory sounds plausible (that the roofers messed up the cap), then I can find a reputable roofer to safely go up there and put the proper caps on.

    I did try to look at it with a drone, but couldn't tell from the video/images if the caps were right, or mounted right.

  2. #2
    Join Date
    Apr 2007
    Location
    Tucson, Arizona
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    I would call out a reputable HVAC company to check the flue. Many Roofers I have met can’t tell the difference between an exhaust fan and a dryer vent, and a flue pipe. An HVAC company can check everything else, and repair the flue with the proper termination cap. Your hypothesis sounds correct with what you are describing. If too much “condensation” is leaking inside the pipe, you may lose heat when you need it the most. The double wall flue pipe pictured on the attic has a 1” clearance requirement, the material should not be touching it. It does sound like the pipe is hotter than expected from your description.
    Did the roofers provide permanent tie off points for workers on the roof? You may want to mention to the HVAC company when you call the 2 story, recent metal roof (very slick, especially when new) and what kind of tie offs are provided so they can bring the appropriate tie off harnesses and safety materials. And not have to leave on your dime to fetch them.
    There are two ways to do things, Right and Again.

  3. #3
    Join Date
    Nov 2019
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    Thread Starter
    Quote Originally Posted by shavedneon View Post
    I would call out a reputable HVAC company to check the flue. Many Roofers I have met can’t tell the difference between an exhaust fan and a dryer vent, and a flue pipe. An HVAC company can check everything else, and repair the flue with the proper termination cap. Your hypothesis sounds correct with what you are describing. If too much “condensation” is leaking inside the pipe, you may lose heat when you need it the most. The double wall flue pipe pictured on the attic has a 1” clearance requirement, the material should not be touching it. It does sound like the pipe is hotter than expected from your description.
    Did the roofers provide permanent tie off points for workers on the roof? You may want to mention to the HVAC company when you call the 2 story, recent metal roof (very slick, especially when new) and what kind of tie offs are provided so they can bring the appropriate tie off harnesses and safety materials. And not have to leave on your dime to fetch them.
    Thanks for your analysis, I'll call the HVAC company. I'll also let them know about the metal roof, though I have no idea about tie-off points or how I can spot them.

    How can you tell that the pipe is double-wall? (I'm just curious, I'm loath to pop it apart if I don't have to).

    "Termination cap" is that the proper term for what I called a "vent cap"? The 'hat' on the flue that prevents birds and rain from entering?

  4. #4
    Join Date
    Apr 2007
    Location
    Tucson, Arizona
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    Quote Originally Posted by RobDiesel View Post
    Thanks for your analysis, I'll call the HVAC company. I'll also let them know about the metal roof, though I have no idea about tie-off points or how I can spot them.

    How can you tell that the pipe is double-wall? (I'm just curious, I'm loath to pop it apart if I don't have to).

    "Termination cap" is that the proper term for what I called a "vent cap"? The 'hat' on the flue that prevents birds and rain from entering?
    I’d assume the roofers would charge for installing tie off points, and you’d know if they installed them.
    The picture shows double wall flue pipe.

    The upper section of the picture where the outside bumps in about 1/4” in a bead that connects to the inner aluminum pipe, and the rivets on the elbow tie the inner pipe to the outside. A single wall flue is just metal pipe and has a 6” clearance to combustible materials, and are not permitted to be installed in an attic. You certainly have double wall flue pipe. I’d guess it’s a 4” from the picture, the sizing goes off of the inner pipe.
    Termination cap is a proper term, there’s also a storm collar that’s only about an inch wide that sheds water away from the flue pipe. And the flashing that seals the flue pipe to the roof deck. Each manufacturer of flues has several different termination caps, for high wind, rain, and specific install challenges.
    There are two ways to do things, Right and Again.

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