Tankless Condensing Vent Pipe Slope

Discussion in 'Tankless Water Heater Forum' started by janderson13, Sep 20, 2013.

  1. janderson13

    janderson13 New Member

    Messages:
    3
    Location:
    Spokane, Wa
    Hello,

    I'm finishing my basement and I would like to pre-install some 4" ABS or PVC for a condensing tankless water heater to be used with my radiant floor. I was thinking of a Takagi or Rheem unit. Anyway, the Rheem manual says that the slope for a horizontal ABS/PVC vent should be to the outside of the building (opposite of a furnace which slopes back toward the unit). I'm guessing Rheem says this because they don't have a condenstate drain on their equipment? The Takagi manual doesn't mention slope but it definetely has a drain on the unit. I'm concerned because where my vent exits my house I have to go veritical for about 1 foot before existing. Attached is a diagram.


    Tankless Vent Pipe.png


    So... I'm wondering do all tankless condensing water heater vent pipes slop to the outside normally? If so, when you have a situation like mine you don't worry about much condensation collecting in the elbow because realistically there is almost no condensation? I'm guessing condenstation really isn't a problem for this reason: if you followed the Rheem manual and slope directly to the outside any condentation would drain out the side of your house and you would have acid water running down your siding?

    Any help greatly appreciated!!!!!

    Thanks!

    Jeff
    Last edited: Sep 20, 2013
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    Ideally, you have LOTS of condensation, it literally could be gallons per day. On some days, with my mod-con, if I'm in the basement, you can literally hear the water flowing through the pvc outlet pipe from the thing and the condensate pump's float switch is tripping regularly.

    That vertical leg would only be acceptable (and maybe not, depending on the specs of the device you choose) if the device had its own condensate pump and collection system. You want to avoid 90-degree bends (excess ones, anyway). Each manufacturer will list the maximum 'functional' length of the air inlet and outlet - elbows equate to a pretty big length.

    Bottom line, select your equipment, then follow the installation manual as to how to run and terminate the connections or you may just be doing it over again. Personally, I'd prefer to have the condensate collection in the unit. Depending on where you can drain it to, you may need to buy the optional neutralization kit for the burner you choose. This is normally only an issue if you have cast iron or copper drain lines (well, if you have galvanized, you've got other problems).
    Last edited: Sep 20, 2013
  3. janderson13

    janderson13 New Member

    Messages:
    3
    Location:
    Spokane, Wa
    Jim,

    Thanks for the reply. I meant no condensation in the horizontal portion of the vent pipe - I would expect condenstation from the unit itself :)
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    Especially if the horizontal section is long, you WILL get considerable condensation, but still will get a surprising amount in the first few feet of the exhaust stack.
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