Air Supply for Tankless On Demand Boilers

Discussion in 'Shower & Bathtub Forum & Blog' started by johnfrwhipple, Dec 14, 2013.

  1. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    [​IMG]

    Hey Terry - is this OK?

    The plumbers at my current job hooked up a on demand hot water tank and did not connect the air intake. Instead they left the metal pipe near the location of the tankless hot water tanks intake location. I see this with gas furnaces but never with a tankless installation. What are your thoughts on this practice?

    Thanks.

    [​IMG]
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    It's a big energy hog...sucking all of the combustion air (and already conditioned air most likely) out of the structure (and through cracks). Whether it is allowed or not, you'd have to read the installation manual.

    If they did not perform a combustion analysis, the difference in having the pipe to supply the air verses being open to the structure could also have the fuel mix off. And, that could vary based on if there were anything else running at the same time (say a furnace, the clothes dryer, the exhaust vents, the stove vent hood, windows open, etc.).
    Last edited: Dec 14, 2013
  3. hj

    hj Moderator & Master Plumber Staff Member

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    Depending on whether the boiler is in a location, (i.e., located in a bedroom or bathroom), where the combustion air MUST come from the exterior the air inlet pipe is usually optional. Using PVC is recommended by the heater manufacturers, but the PVC pipe manufacturers do NOT advise using it.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Can't tell which model, but the manual which probably covers yours, on page 32 discusses what may happen if you do not direct vent the thing http://www.navienamerica.com/__DATA/ProductDocument/2012/11/30/[4]_3.%20Operation%20Manual_NR_NP.pdf and the venting requirements and issues continues on for multiple pages. Did they install the inlet air filter?

    It looks like the forum software didn't recognize the entire link...you could try cut and paste, but it may not work. It's a big file, over 70M.

    I do not know if it is code, or just the industry recommendation, but you should have 50cuft of volume/1,000BTU input for your total burners that could be running in the room where the appliance is installed if you do not have direct outside air connected for that purpose. I know when I looked at it for my home, I did not have enough volume to install my boiler without the recommended outside air inlet being plumbed to the unit. The room also contains the washer dryer, and I barely had enough volume for the dryer. Keep in mind, this could include a furnace, clothes dryer, and potentially other appliances in that area.

    The installation manual says that it leaves the factory pre-adjusted for having both ports plumbed with pipe. They did not indicate checking the combustion efficiency, which is typical of most gas fired burners, but I may have missed it.
    Last edited: Dec 15, 2013
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    It seems that John is ignoring my suggestions, even when well-founded. I did not search Canadian codes, but to help support my assertion that drawing air from inside, while it can work, has both energy efficiency issues because it is pulling unconditioned air into the structure, and from a safety issue, if the space is not large enough (you never want to create negative pressure in a dwelling). But, here is one source from the US that lists the code requirement of at least 50sqft/KBTU for any gas burner http://dsps.wi.gov/Documents/Industry Services/Forms/UDC/sb-UDCApril01SummaryWorksheet.pdf
  6. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Location:
    North Vancouver, BC
    Swung by to check on the drywall progress and found that the plumbers where called back.

    They removed the galvanized 4" pipe that was originally for the furnace and slipped in a new air supply line. The whole thing pipe in ABS pipe.

    City Inspector was scheduled to view the work but as yet have not heard from the home owners if the install was approved.
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