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Insufficient slope vs Extending concentric vent past deck for Rinnai RE199iP Tankless WH?

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yevc
yevc Member Posts: 4
edited June 10 in Domestic Hot Water

I'm replacing an existing tankless WH with a non-condensing Rinnai RE199iP tankless WH and would like to use the Ubbink concentric vent Rinnai recommends. The water heater would be in an awkward place - roughly in the middle of the an exterior block wall. Behind the wall where the WH will be installed is a deck, open on 2 sides, with about 4ft of clearance over grade, so running the vent through the wall (the most direct option) would put it ~1ft under a deck / ~3ft above grade (this is how the current WH is power vented - no intake). Running the vent to the left or right through a joist bay will require approximately 15ft of pipe, and by the manufacturers directions requires a 1/4" per foot drop either toward the outside or toward the unit with a condensate drain. In either scenario that requires approximately a 3 3/4" drop which won't be possible due to the width of my rim joist (2x8) - the best I could do would be ~1 1/2". Although that isn't to manufacturer spec, has anyone experienced issues with such a small drop? My other option would be to run the vent through the wall behind the WH, then run another 15ft or so of the concentric vent pipe under the deck so the cone sticks out past the edge of the deck. I have been unable to find any information about limitations on running the concentric vent pipe on the exterior of the house. Any advice is highly appreciated!

Location: PA climate Zone 5

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  • Intplm.
    Intplm. Member Posts: 2,037
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    Fifteen ft. is not a terribly long distance of a run. However, Rinnai has a great set of guidelines, and it would be best to contact them.

    That being said, you can place this type of unit almost anywhere. You state that you are using this as a water heater. If so, you can put this unit in a pantry or other room with an outside wall and connect the hot and cold water from there. This way you you won't need the pitch but can run the vent directly outside.

    I don't know what part of the world you are from but they also make units that can be installed outdoors, where the climate allows. This type of unit has a vent built in and can hang on an outside wall.

  • yevc
    yevc Member Posts: 4
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    I tried contacting Rinnai but they were not very helpful unfortunately. The place I am installing it is really the only reasonable place to put it (I am replacing an existing ancient tankless unit - which power vents under the deck currently). I'm in Pennsylvania, USA - it's a cold climate so an outdoor unit is not an option at the moment. I'm leaning toward venting it directly out of the wall behind it and then extending the vent pipe (outside) 15ft past the edge of the deck - I'm just having trouble finding any information on whether or not a concentric vent pipe can be used in this manner.

  • hilltown
    hilltown Member Posts: 20
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    the Ubbink non condensing vent material can not be installed in that fashion. The only part that can be exposed is the black vent termination and there should be the least amount of the white part as possible, just a few inches really.

  • hilltown
    hilltown Member Posts: 20
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    if it’s not in the install manual don’t do it or warranty is gone. Wanted to do something similar as a deck was built after the install a few years later. You need 3’ from a soffit or overhang above and usually if your venting under a deck you don’t have it, simple solution seemed to be to run the pipe in the manner you describe. Didn’t fly and we needed to vent out another wall. Manufacturer states that the tankless manual supersedes their instructions.

  • yevc
    yevc Member Posts: 4
    edited June 11
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    I just found this quote in this Ubbink document about the concentric vent:

    "The Ubbink Rolux® white vent extension material is designed primarily for indoor use. If
    used outdoors, the material should be protected for UV-radiation (direct sunlight)."

    The way my house is oriented, the white part would actually never receive any direct sunlight. I'm thinking as an additional countermeasure, I could paint it.

    In my case, the "cone" would be sticking out past the deck so there would be no overhang above it … or is that 3ft clearance required in any direction? Meaning it would have to stick out 3ft past the outer edge of the deck?

  • Intplm.
    Intplm. Member Posts: 2,037
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    Does this unit have a two-pipe venting option? If it does, that might be the way to go in your particular situation

  • Intplm.
    Intplm. Member Posts: 2,037
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    If that's the case, and you do not already own the Riannai. I would find a unit that allows for two pipe configurations. The two pipes would be smaller in diameter and allow for the proper pitch.

  • dko
    dko Member Posts: 621
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    Rinnai will have a concentric to twin pipe adapter for their unit

    Intplm.