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Tankless water heater venting questions

I'm purchasing a Rinnai RU98iP tankless water heater and will be venting it through the wall using concentric pipe. The area outside where it will vent is under a deck which is about 6 feet off the ground. My question is how far below the bottom of the deck is it safe and code compliant to install the vent in Northern Virginia? I've been able to find out the 4' minimum distance from doors and windows but can't find anything about under a deck. I contacted the manufacturer but they had no input on venting under a deck. They said it is possible as long as it follows local codes. Thanks in advance to anyone offering answers.


  • JStarJStar Member Posts: 2,752
    I thought that it was 3ft. For me, though, I would never vent it directly under a deck. Besides the safety hazard, it will cause a lot of condensation, that will freeze up or rot the deck. In this situation, we'll extend the venting to the outer edge of the deck.
  • kyarbokyarbo Member Posts: 3
    Extending the vent is something I hadn't thought of. The deck to the right of the proposed vent location is around 20' but to the left is about 6'. The edge of the deck is about a foot from a window unfortunately, if it were then extended out 3'-4' from the side of the house, adding quite a bit of length to the pipe, what other problems would this scenario create?
  • JackJack Member Posts: 1,044
    Your best option for extending the vent out past the end of the deck is to install the vent pipe with the concentric and to sleeve it with a piece of 6" PVC. That has worked well. Your other option is to pick up the free PVC adapter Rinnai now offers. You can then run PVC as a vent. For the longer vents, from a cost standpoint, that may work for you.

    Termination clearances under and overhang/deck is 3' this is more to prevent recirculation of flue gases than a combustion clearance. If the deck is open all around you should be ok with that. The caveat to that, in my experience is how clean is it under a deck and will you end up storing gear under there or are bugs going to decide to take up residency in your vent.

    I much prefer the concentric vent but the PVC is a new option on Rinnai.s condensing units
  • kyarbokyarbo Member Posts: 3
    The deck is open on 3 sides, no plants grow under it and the area will not be used for storage. Venting it 3' below the deck bottom would leave about 2' below the vent to the ground which would work well for this install.
  • RobGRobG Member Posts: 1,850
    I would contact the local inspector and ask him. I hate having to redo ANYTHING.

  • JackJack Member Posts: 1,044
    The inspector "must" accept the manuf installation instructions. Sorry, I almost timed out on this post. I re -read that first sentence and was simply hysterical...for a long time.

    I think you will be fine with those clearances. Just make sure you don't have a lot of debris around the termination.
  • RobGRobG Member Posts: 1,850
    I don't think the manufacturer has a "venting under deck" section in the installation instructions. I have gotten verbal approval over the phone from many manufacturers but when I asked for it in writing, no-go. Ask the inspector first, and get the inspectors name. There is no guarantee that the inspector you talk to on the phone will be the inspector who comes out. I worked in NOVA for many years and you have to cover your butt.

  • JackJack Member Posts: 1,044
    "Get it in writing" those clearances are in writing in the Installation Manual. 3' below an overhang. A deck is an overhang. Rob, I understand what you are suggesting, but Installation Manuals are carefully vetted documents that are approved by the testing agencies and getting a manuf. to say more than what is actually written in the document is really difficult to impossible to do.
  • RobGRobG Member Posts: 1,850
    edited September 2014
    Interpretation, Interpretation, Interpretation. I interpret an overhang to be a cantilever, not a deck. Cantilevers don't have slots in them with chairs above them. if you had had a cantilever on a home you would still have to maintain clearances from windows and doors. I personally would not do it without checking first.

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