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Thoughts about venting

last month

I looked in instructions and found this chart. It has venting at 161 inches. I have 207 so I am guessing that is why the pressure switch tripped. Your opinion please.

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Comments (10)

  • last month
    last modified: last month

    Our opinion doesn't matter. What do the instructions say?


    You gave us no information. What diameter pipe did you use? How many elbows? What is the allowed equivalent length at that diameter?

    You don't get to be creative with the venting...it can kill you.

  • last month

    Sorry first time posting. Here is the other chart. I used 3 in and 2 elbows.


  • last month

    It ran for about 2 hrs and tripped the pressure switch. Kept it open.

  • PRO
    last month

    I believe you have a condensing-type gas furnace. If it ran for two hours prior to shutting down, there's a good chance of condensate build up in the exhaust pipe. It needs to be pitched and drained.

  • last month

    it is sloped at 1/4 per foot.



  • last month
    last modified: last month

    You have exceeded the allowed length. You can't move forward with troubleshooting until you fix that problem.

    Also, did you include any elbows outside in your elbow count?

  • last month
    last modified: last month

    Based on what I can see, you should be OK with 3" pipe on a 60,000 BTU furnace. You may have a bad switch(?) Also, your clear condensate drain tubing looks a little small(?)

  • 29 days ago

    @sktn77a I do not see what you are seeing. I see the maximum length as being 161 in and he has 207 inches.

  • PRO
    29 days ago

    Maximum pipe lengths are typically tabulated in units of feet-- not inches. If you look at the footnotes under the tables, they note to add a certain number of feet for each elbow which is the "equivalent length." I can't see any units specified for the table entries, but it wouldn't be appropriate to mix units.

    I've never seen an installation where the supply and exhaust were drained with tee-wye fittings and dedicated drain lines. They add complexity and pressure drop compared with the more conventional approach for draining condensate.

  • 29 days ago
    last modified: 29 days ago

    @Charles Ross Homes

    Yeah, I feel completely foolish that I didn't catch that. I relied on the OP's information without thinking. Of course it's in feet, not inches.

    I've never installed a condensate drain like that either. It seemed pretty bogus, but I didn't want to go there. Without a trap it would be a source of CO. And unless the inlet is such that rain is entering it, it doesn't need a condensate drain at all.

    The thing is that the install looks like it was not entirely legit, and I'm a lot less supportive of DYI on a furnace than most plumbing. Just my own bias.

    OP: Get rid of those condensate traps and see how it works. Then support the vent lines with something more legit than a 1x1 held up with a couple of drywall screws tacked to a door frame. Are the joints primed and glued or just dry fitted at this point? You don't want any chance of them coming apart.