Reducing intake/exhaust sound outside home

Discussion in 'Boiler Forum' started by doughpat, Oct 31, 2020.

  1. doughpat

    doughpat New Member

    Joined:
    Sep 11, 2020
    Location:
    Bend, OR
    Hi all -

    I've got a 110k BTU Lochinvar combi-boiler installed in garage. It vents via (2) 3" PVC pipes which combine into a concentric vent pipe that penetrates the wall.

    The unit is significantly louder than I had hoped, and part of the issues is just site-location (i.e. my neighbors bedroom window is about 10' away....).

    I know its going to make some noise, but wondering what I can do to dampen the noise. The installer had said something about basically making a "glass pack" type muffler, involving a wider diameter PVC pipe packed with something to help absorb some sound.

    I have very good access to the pipes before they enter the concentric vent. There's about 8' of (sloped) exposed pipe.

    [​IMG]

    Wondering if anyone has any tips on constructing something like that. A couple of specific questions:

    -What would you pack the muffler with?
    -Would you do both intake and exhaust, or would one be the bigger culprit?
    -I assume you'd use a 3" to 4" (or 3" to 5?") adapter, and leave the inside pipe in place, but with lots and lots of holes/slots in it. But how can you keep the 3" pipe in place? Wondering if there are some more-obscure pipe fittings that might accomplish this.

    Anyway thanks in advance -- new to this forum and am amazed that I didn't know about this sooner.
     
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Any chance you can extend the intake & exhaust piping outdoors and go vertical prior to the concentric vent? Blasting noise at the sky has a lot less impact on your neighbor than a vent terminator directed at the wall/window.

    There are length limits to exhaust vents that include the "equivalent lengths" of every ell or tee or other fitting along the path. I'd be hard pressed to estimate the equivalent length relative to 3" PVC of a glass packed muffler of larger diameter, but I'm sure it's a LOT longer than it's physical length, and the density of the packed fiber would affect that dramatically.

    A glass-pack muffler on the intake would risk bringing aerosolized bits of glass fiber into the combustion chamber. If going that route do it ONLY on the exhaust side.
     
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  4. doughpat

    doughpat New Member

    Joined:
    Sep 11, 2020
    Location:
    Bend, OR
    Could I put a 90 on the exhaust (center of the concentric vent) and accomplish the same thing without re-routing (and the subsequent siding/wall fixes)? I'd need to get up on a ladder and see about that but I don't see any immediate reason why not. Currently it vents directly out -- horizontally. The air intake is on the bottom side of the 'bell', drawing fresh air in next to the siding.

    Thanks for the tip on the fiberglass....thats a very good point. If I were to do something on the intake side, it'd need to be packed with something that won't 'aerosolize' (or break up in any way). I wonder if some kind of metal mesh wrapped around the inner pipe?
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Take a look at the terminator, see if there isn't an easy plumbing solution.

    It doesn't take a high air velocity to break fiberglass fibers releasing microscopic shards. Even the indoor to outdoor air pressure differences when running an HVAC system can be enough to pull shards out of attic fiberglass batts through recessed light fixtures if they're not designed and installed to be air tight.

    Metal mesh isn't likely to provide a lot of benefit, but I've never designed a muffler- don't know if it would be enough to make it worthwhile. The amount of turbulence induced by pulling gases through a mesh would still be pretty high, creating a very long "equivalent length".
     
  6. doughpat

    doughpat New Member

    Joined:
    Sep 11, 2020
    Location:
    Bend, OR
    Will look at the end to see if I can just stick an elbow and aim the sound up. That seems to be a good starting point.

    But regarding your other statement regarding turbulence by pulling gases THROUGH a mesh: If I understood correctly, the gases wouldn't, in any significant amount, actually go through the holes in the inner tube. The holes would allow sound waves to dissipate out through the holes, into the mesh...thus hopefully deadening them. I'm sure there would be some additional restriction (i.e. equivalent length) compared to smooth-wall, but I wouldn't intuitively that there'd be a huge amount of change there. I would think the gases near the edge (i.e. those rubbing the pipe wall) would be disrupted a bit, but not much.
     
  7. doughpat

    doughpat New Member

    Joined:
    Sep 11, 2020
    Location:
    Bend, OR
    Just need to find out the diameter....hoping its standard PVC dimensions.
     

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