Direct Vent Question - Vent near AC Unit

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by philtrap, Jun 19, 2013.

  1. philtrap

    philtrap New Member

    Messages:
    66
    Location:
    Long Island, NY
    Folks - My Second Question here and Thanks for your support.

    See attached photo.

    The only spot I could vent my boiler exhaust is near my AC unit. The AC unit will not be working when the boiler is working (I hope) since I only use the AC in the summer and heat (boiler) in the winter. The AC unit blows air up, but it really doesn't hit the vent. Is there a different type of end pipe I can use, or is the way it's installed OK?

    Thanks, vent.jpg
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    I don't think it will affect the a/c. It is possible that the exhaust could be slightly corrosive, and that may be an issue - it depends on whether it meets the offset requirements laid out in the manual. If it is far enough away, that effect should be diluted enough to not be an issue. But, it may be too close to either the corner or an operable window. The installation manual usually has some very specific requirements on this. The danger is that the boiler might be venting while you have a window open for whatever reason and you could be pushing CO into the house. The corner doesn't help, and the winds can do weird things around corners.
  3. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,071
    Location:
    Maine
    Its too close to the corner and the window. The installation instructions are crystal clear regarding proper vent clearances. How did you get that installation inspected and passed? If you didn't bother with the inspection process you should know that if there is ever an issue with the installation, ANY issue that causes property damage or personal injury, your insurance company will drop you like a hot rock.
  4. philtrap

    philtrap New Member

    Messages:
    66
    Location:
    Long Island, NY
    Tom - The Installation instructions say one foot away from the window and 3 feet from a corner. It is in compliance with that. I can run it up thru the roof. What do you think?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    If you've meet the manufacturer's offset and clearance requirements, and the termination is an approved type, it should be fine. You might find that leaving it there with the motion sensor on the flood lights, when the boiler is running, it may turn the lights on! In that case, through the roof may be a better option.
  6. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    Aren't you using the boiler to heat hot water? (If not, you probably should, but that's another topic.)

    I wouldn't sweat the location relative to the AC compressor- even if condensing exhaust condensate managed to finde it's way onto the AC unit, the dilution factor of rain & snow would pretty much render it neutral, now that the acid-rain issues from power generation have been taken care of. Vent terminals for direct venting have to work in 50mph gales anyway, and there's no way the turbulence on the side-stream of the AC fan would approach anything like what you'd get out of a mid-winter nor'easter or a passing tropical storm. It's a forced-draft system, it takes a HUGE amount of wind turbulence to mess it up.

    As far as clearances, in Canada to meet code you'd need to be 36" away from any operable window or door, but in the US a mere 12" cuts it unless specified differently by local code. If you're more than 36" away from the wall it would cut it even in Canada. Local codes (or the manufacturer) may have restrictions on distances to interior or exterior corners, but there's nothing enshrined in national codes on that, though parking it at an interior corner near a window could have some build-up issues at 12". There's nothing (other than glue, perhaps? :) )to prevent you from rotating/angling the vent away from the house to guarantee that it's blowing away from the window.

    Most manufacturers want to see the combustion-air intake on the same wall as the exhaust to avoid wind-driven pressure imbalances from interfering with it's operation during those 50 mph gales, and will specify min & max clearances. If that's not a coaxial intake/exhaust vent, but exhaust only, where's the intake, and does that meet the manufacture's instructions?
  7. philtrap

    philtrap New Member

    Messages:
    66
    Location:
    Long Island, NY
    Thanks both Jim and Dana for your input. My biggest concern was the a/c compressor unit blowing air up. I don't have hot water now since my hot water heater is new. I may add it once the hot water heater goes, so maybe I would be best to run both intake and exhaust up thru the roof right above the spot light. The intake is not finished yet, but my main concern was the a/c unit blowing up. What do you think about this (See pic below)? The vents would be at least 3 feet from any window and at least 3 feet from the wall.

    I would raise the outlets to 2-3 feet above the roof for snow.

    (See Tom, this is how a forum works) vent2.jpg
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    Other than two new holes in that roof, it may eliminate some potential issues (I think it will likely be okay where it is, but the roof has advantages, too).
  9. MACPLUMB 777

    MACPLUMB 777 TROJAN WORLDWIDE SALES RP

    Messages:
    679
    Location:
    Houston, Texas, United States
    The roof top would be correct way to do the vents, depends on what windows are higher on that wall
  10. philtrap

    philtrap New Member

    Messages:
    66
    Location:
    Long Island, NY
    OK folks. I didn't like the AC unit blowing air up into the combustion vent, so I moved it to the roof. See the photo below. I also placed the air vent intake outside (it was inside the shed). The direction sketches always show the intake vent higher than the combustion air vent. Do you think it matters? I have a unique situation since the only way to vent the boiler is thru a shed that's built into the corner of the house. All other requirements are met. 36" away from corner walls, 12" away from windows, high enough for snow fall plus some. The vent vertically thru the shed roof is the combustion vent and the one to the right side of shed door is the intake fresh air.

    The a/c unit in the wall does not function. I now have central AC
    The central AC blow is behind the bushes. You can see it in the first photo I posted.

    photo (1).jpg
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    The intake and outlet are far enough apart, that I do not thing you'll have any issues. In most installations, they are run in parallel, so the height and offset is much smaller, so placement is critical.
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