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direct vent noise question

bigwilly104 Member Posts: 50
I know it sound odd but for condensing apliances that use PVC flue pipe I have used a muffler sold by specialty A/C Products in Benica California. I buy all my forced air equipment from them It may be a Trane product but I am not sure. It looks like a piece of 12" pvc about 18" lon with reducers to 3" or 2" on either end it is lined with closed cell foam and I think it has a internal baffle. It does not add any more lenght to your vent length other than its own. It works great and if I remember right it cost less than a 100 clams.


  • allenh
    allenh Member Posts: 117
    direct vent noise question

    We just had direct vent boilers installed. This is the third house with direct vent and all are different manufacturers.

    Does the higher the efficiency mean a louder exhaust?

    Attached is a what the homeowner has to sign along with plumbing permit for the work performed. Has anyone else seen something similar to this form?
  • Brad White
    Brad White Member Posts: 2,398
    Welcome to the People's Republic

    You could always move :)

    "Does the higher efficiency mean a louder exhaust?" you ask. Not necessarily and it depends on the manufacturer.

    Funny you mention this issue, it came up in an office discussion today.

    Here is what I posted in-house:

    I think it time we ask manufacturers to provide sound and terminal velocity data. It is all by manufacturer and type.

    With furnaces, many of the blowers are high RPM and small diameter venting, relatively, so there is your noise. Market is to fit these into older homes initially so small venting is a plus there. Some are indeed noisier than others and this can carry.

    The Viessmann Vitodens, (when firing in summer making domestic HW when there is no plume) you have to put your ear within a foot of the vent to hear it running or not. In winter there is a plume and yes, icicles. The termination screen is designed to keep the nozzle clear of ice. In colder climates (Alaska and Canada) they recommend a special termination cap or snip away some of the cage hoops from the standard. In other words, they see the potential for problems and have addressed them at least in that line.

    It may not directly address your question, but seriously, "it all depends".

    Having done enough engineering in the PRC, that ordnance and affidavit you posted seems to have let up a bit. Used to be that the requirements were so strict (40 dBA after 11:00 PM) that were exceeded by normal background levels.

    Headline: "Cambridge Outlaws Flatulence".

    The big question is, how does a HO verify their sound performance unless you hire an acoustician -let alone mitigate it should it fall short?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Weezbo
    Weezbo Member Posts: 6,232
    I would say that it is unlikely that a direct vent appliance,

    would exceed or even approach the intent of the civility clause written within the regulation.

    Tjernlund ,might say it in some other way...
  • allenh
    allenh Member Posts: 117
    ah but who would think about noise

    until after its installed. Of the 3 that we have in different locations these are the quietest.

    When you are talking about a stand alone direct vent water heater the btus are say 40k. All 3 different model boiler we have installed have had input btus of 65 to 110k and all had internal fans.

    Does anyone know if larger / smaller flue pipes would make a difference in sound? And if longer or shorter runs make it quieter?

    If more efficient heating systems are the way this country is going, direct venting noise is going to have to be quiet in city applications.

    This location does not have people that close - whew. And this particular boiler is quiet when running which is great.
  • Direct Vent Sound Levels

    There really is no way for the manufacturer of a direct vent boiler to make a determination of expected sound levels. When the induced draft fan is back at the boiler, there are too many variables that come into play by the time the flue gasses get to the termination fitting. Those are relative to vent distances, vent methods, types of vent materials, numbers of turns, etc. I would suppose that aftermarket devices such as power venters from either Field or Tjernlund could be equipped with sound level ratings due to the fact that they are located either inside close to the point of discharge or outside the building. Those are for the best part fixed parameters. There would also be fixed parameters on devices that vent directly through the wall such as fireplaces and the like.

    Sound is a very difficult thing to deal with indeed. I live a small community in Southern RI where house lots are small and buidings are fairly close together. On my block we have an Insurance Agency business central to the block with a fenced-in parking lot that abuts just about everyone elses properties at the rear bounderies. One of my neighbors (with an apparent acute hearing condition) has been complaining for years about hearing water dripping into a storm drain at the rear of the parking lot that abuts their property as well as mine.

    I received a letter from the agency stating that during one week this past September, there would be a fence company removing the existing stockade fence and installing a tighter and higher one in place of it at a cost of several thousand dollars to appease the abutting neighbors. What they didn't know is that that particular neighbor sold the house and moved to the hills of New Hampshire where they no longer have neighbors! Where you are located is a community where buildings are very close together, budgets are extremely high and tolerances to noises are low. Thus the sound ordinances.

    Glenn Stanton

    Manager of Technical Development

    Burnham Hydronics

    U.S. Boiler Co., Inc.
  • Brad White
    Brad White Member Posts: 2,398
    Manufacturers Sound Data

    Hi Glenn!

    Actually we ask for this all the time and receive it for various components, be they fans and air handling equipment, cooling towers and chillers. The tests are done to certain standards in a room or outside with noise filters from various distances. These are published in tabular form.

    No manufacturer can expect to know that happens beyond the confines of the installation, but with baseline data, an acoustician can make a determination of what noise level would be expected at the property line.

    (Square of the distance rules plus any attenuating effects of vent piping along the way for example.)

    But the "raw" data is determinable. I think with any power-vented appliance this could be done. Not atmospherics nor power burners venting into vertical chimneys, I think that is reasonable to say. But side-vent appliances, that I can see. And hear.


    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Brad White
    Brad White Member Posts: 2,398
    Generally Speaking

    A larger flue pipe would be less noisy than a smaller one, but regardless the manufacturer has to sanction the size per the application. Also if combustion air is ducted in and if the exhaust were to be larger and separate, an adverse pressure differential might be created. Often the pressure switches work off differential between incoming air and exhaust, hence the need for nearly equal pressure drops with each. "Balanced flues" is the term. Not all manufacturers subscribe to this requirement but enough do.

    More elbows would also tend to knock down sound but count against overall venting lengths. Longer flues would also tend to attenuate somewhat.

    At least you have to the property line to dissipate any noise. Fail that and I will see you in the Re-education Camps. :)
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Joannie_14
    Joannie_14 Member Posts: 22
    Direct Vent Sound

    My two cents, because I've been asked for this a couple times:

    We can measure sound in our lab. One issue we have is that customer asks for "dB level" which means nothing without telling us how far away they want us to measure. All of them have said something like, "I don't care how you measure it. I just need a number to put on this form." I don't know of a standard to measure this by.

    The bigger issue, though, is that the ambient sound in our lab (even after hours when it's pretty quiet around here) tends to drown out the appliances that we have tried to test on, at 5 or 10 feet away. I think our only option is to take our products to a lab that is set up for acoustics, but it's tough to justify that expense when we can't tell the lab how/what to test.

    This probably doesn't help much, but it's what we've run into here, (where the office din tends to be louder than our direct-vent appliances....especially that squeaky door behind me).


    Laars Heating Systems Company
  • Brad White
    Brad White Member Posts: 2,398

    we ask for dBA ratings which are A-weighted decibel ratings. The scale weighting makes these match the range of the human ear.

    The measurements are taken usually at 5 feet and on each side of an appliance, including the top. For cooling towers, 5 feet and 50 feet distance measurements are given. These work fairly well and the instruments are not too sophisticated to make them.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Joannie_14
    Joannie_14 Member Posts: 22
    That's Helpful

    Thanks, Brad. That's more specific information than I've ever been able to get from someone who is asking. We always assumed a distance of 5-feet, because it seemed like that would be logical. Unfortunately, we don't usually get asked the question by the one who is really asking....we're usually a few people away.

    Have a great weekend!
  • Dan Sedens
    Dan Sedens Member Posts: 48

    David Brogan Strike Again!!!
    I actually just did an installation this past week and his first question was had I filled out the noise ordinance form. Fortunately my boiler didn't fall under parameters as neighbor was a public parking lot. That was the first I had heard of it. His story as to why it came about was very interesting however, but it definitely has to do with the Peoples Republic. Have to keep that in mind next time.
  • Brian_57
    Brian_57 Member Posts: 6
    seen simialar

    papers handed to me when getting a permit app. Doesn't pertain to the noise of the boiler but is to make you aware that that town has a noise ordanace that prohibits construction work after a certain time. people dont want guys running saws, drills, or hammering all night long.
  • Timco
    Timco Member Posts: 3,040

    I checked a furnace for a friend and found that tightly strapping the long, straight run helped with resonating sound, and removing the jumper causing it to stay on high-fire helps quiet the exhaust...

    Just a guy running some pipes.
  • tim smith
    tim smith Member Posts: 2,752
    Sound levels

    I have had way too much experience with this of late. Had to deal w/ an a/c unit we put in 7 yrs ago but new neighbor who bought the house did not like the condensor sound. Ended up putting up a sound wall to bring our db levels down to acceptable. Brad, I thought the standard ARI measurement was 3ft? Just wondering. Side note: we also had to go out at midnight w/ acoustical engineer in a community where Microsoft execs live and do certified testing on condensors so our customer could run their a/c units at night, yuck.
  • Brad White
    Brad White Member Posts: 2,398

    The distance I have always seen has been 5 and 50 feet but the ARI standard (270 I think) does not have a specified distance. The 5 and 50 foot distances show up in manufacturer's selections and published sound data.

    An acoustical engineer told me that the 5 and 50 feet is arbitrary but is scalable based on distance and logarithms so can be made comparable across different readings of different equipment. Not to say you could not rate your equipment at three feet. May well exist, I have just never seen data at those distances.

    You do need a minimum distance to allow initial spread of sound. For exaggerated example, if you put the microphone inside the cabinet, you would gather as much reflection and conflicting sound from fan, compressor and valves compared to some distance away once they mixed and dispersed.

    I always found it rather intriguing that when new folks move in to a neighborhood knowing of a potential noise source, they complain. I can understand moving in during the winter then finding summer noise levels with perhaps outdoor activities and some open windows to be unknowable in winter.

    But we have had cases of folks moving next to a rifle range or better yet, an airport (hello?), then complain bitterly. Yet never questioning why the property cost was 30% less than other comparables miles away in the same zip-code.

    I understand the "quiet enjoyment" legal principle, but really, an airport? Who knew? :)
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Bruce Stevens
    Bruce Stevens Member Posts: 133
    Alway gets me is existing noise level with new neighbors

    Brad said
    "I understand the "quiet enjoyment" legal principle, but really, an airport? Who knew? :)"

    We had a guy move in next to a farm and after six months wanted the town to make the farmer keep his Roosters from crowing until after 7AM after all there was a noise ordinance in town
  • Brad White
    Brad White Member Posts: 2,398
    I bet the new neighbor was also

    up-wind of the chicken farm.

    The only way to get a rooster to stop crowing is a technique called "fricassee" or similar approach. Sage, garlic and butter optional.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Kal Row
    Kal Row Member Posts: 1,520
    nice to use lochinvar's...

    they are not very noisy and with the 100ft allowed Len, i can usually get it to the middle of the roof line, have had more complaints from the HOs about popping noises, as a long outdoor exhaust PVC expands a lot and will grab/release on the strut clamps going up the side of the house and make “pop” sounds, so now I wrap the clamps with Teflon tape first - live and learn
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