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CSST - The Cause of Harmonic Fog Horn Noise

Ironman
Ironman Member Posts: 7,088
I literally have hundreds of hours of field experience dealing with mod/con boilers making an intermittent fog horn noise. While adjusting gas pressure and co2 MAY alleviate the condition sometimes, the cause is definitely from CSST being used.

Recently, we installed a steam boiler where one had been removed 10 years prior. Keep in mind that this is an atmosepheric boiler. In order to get it running late in the evening, I took a 20 foot coil of 3/4" CSST and used it to temporarily get the boiler running. The boiler fog-horned - something I'd never heard an atmosepheric burner do. A couple of days later, I went back and hard piped the gas with black iron and the fog-horning immediately was gone and has never returned.

It's the combination of CSST and negative pressure burners that causes the harmonic noise in mod/cons. If adjustments won't clear the problem, remove or enlarge the CSST.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
HVACNUTkcoppZmanMark EathertonTinmanayetchvackerSTEVEusaPA

Comments

  • ratio
    ratio Member Posts: 3,338
    IDK much about modcons, but I've heard CSST flex lines whistle when used on unit heaters before. After I shot down the plumbers' cure ("I'll just turn up the regulator"), I found that I could lessen it somewhat by bending the flex around. As they were way longer than necessary this worked out ok. They were just within the mfgr's limits IIRC, if they had exceeded them I would have been able to push for larger ones.
    gmcinnes
  • clammy
    clammy Member Posts: 2,832
    i can see csst being a issue in some cases which the csst may be undersized increasing the velocity of the flow causing the hog forn ,but i myself have had the dreaded fog horn and it was all black pipe and properly sized on more then a few jobs and where able o fine tune them and on 2 the offset differential had to be adjusted then and only then did the fog horn finally disappear .the only thought that goes through my head is there are many mod con that come with a stainless tubing connecting to the gas valve which is usually only 1/2 .i feel in some cases yes it s csst causing the isssue but in others its combustion adjustments .I personally never use csst and i was trianed many many ions ago when it was being sold for propane or higher then normal gas pressure to enable you to run 1/2 or 3/4 then put a regulator at each appliance way before stray lighting and bonding became a issue .I still see alot being used and usually the boiler .furnace or roof tops and usually that csst install skill follow with either a crappy boiler ,furnce or roof top install usually used by the unskilled ,profiteirs and the lazy or mostly trunk slammers .In closing i have always enjoyed ironmans views and opions, respect his fine workmanship and quality installs but in my mind i cant accept that csst is to take all the blame and some times feel that in my area most is done by rules of thumb and not math and charts unfortunaly .On another note i dont go straighten out others contractors combustion issues on mod con install everybody thinks you should do it for free being they paid some one else already and you all are one big brotherhood ,lol .Usually there are so many issues aside for the foghorning form undersized gas lines improperly pipe the list goes on and on there are alot of non reading mechinacs afloat plus no one wants to pay and for free i can work anywhere instead i ll watch cartoons or weather permitting go fishing .Peace and good luck clammy ps to ironman thanks for your always insightfully post always enjoy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
    gmcinnes
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,169
    @Ironman thanks for the information. I usually try to stay away from CSST. The sizing charts are from the manufacturers who knows if they cheated or not?? I suspect the corigations slow the flow more than they are telling us. And it must be turbulant
  • Bob Harper
    Bob Harper Member Posts: 959
    Try no-whistle flexible gas connectors. See Rhett Rasmussen demonstrate here https://www.youtube.com/watch?v=bJ26O20gIX4
    They work for whistling so perhaps they'd work to dampen or buffer the harmonics from high flow CSST. The other thing to look at is sizing/ gas velocity.
    Ironman
  • Ironman
    Ironman Member Posts: 7,088
    I wanna add that most flex connectors are indeed CSST and can be the source of the harmonic noise.

    @Bob Harper
    Thanks for the video. Where can these connectors be purchased?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    kcopp
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Experienced the same thing on an atmospheric many years ago. H.O. said if we didn't get it fixed, that he was going to consider legal action, good incentive to find a solution, which was to eliminate the flex connector. Sound resonated through the whole house, and was at a pitch that was driving the owner crazy

    ME.
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
    ayetchvackerjpm659er
  • Tim McElwain
    Tim McElwain Member Posts: 4,558
    We found many years ago that whistle or moaning with connectors could be eliminated if you put one coil in the connector instead of a straight run.
    NY_RobIronmanratiokcopp
  • Bob Harper
    Bob Harper Member Posts: 959
    http://www.dormont.com/products/c
    Dormont invented the flexible gas appliance connector. It differs from CSST in that it is a "connector" listed to ANSI Z21.24. It cannot exceed 3 ft except for ranges and dryers and cannot penetrate walls, floors, ceilings, etc. and the fittings must be "accessible" unlike CSST, which can be concealed and is listed to LC-1 as gas piping. It is constructed similarly. One of the simplest things to do is to use a larger diameter connector, which reduces the velocity and thereby the turbulence. You can check with hearth and restaurant supply houses or online.
  • DZoro
    DZoro Member Posts: 1,048
    @Tim McElwain Have you ever tried a loop with CSST?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839

    http://www.dormont.com/products/c
    Dormont invented the flexible gas appliance connector. It differs from CSST in that it is a "connector" listed to ANSI Z21.24. It cannot exceed 3 ft except for ranges and dryers and cannot penetrate walls, floors, ceilings, etc. and the fittings must be "accessible" unlike CSST, which can be concealed and is listed to LC-1 as gas piping. It is constructed similarly. One of the simplest things to do is to use a larger diameter connector, which reduces the velocity and thereby the turbulence. You can check with hearth and restaurant supply houses or online.

    But it IS made of CSST and is subject to the same arcing/ignition potentials, no? I think that is the point Bob Boan was making. In the case where I was involved, the CSST arc where ever it came close to a properly grounded/bonded steel (I beam) structural component. When the fired department showed up, the home was fully involved in the basement and the attic, and they were less than 10 minutes away.

    ME

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Leonard
    Leonard Member Posts: 903
    edited February 2018
    In past I got the same loud howl using a pool hose for a vacuum cleaner hose out in the garage. Guess it's the corrugations are larger on pool water hose than vacuum cleaner hose, and you get a bunch of "smoke ring" vortexs in the corrugations

    Would GUESS changing the gas pressure would change the pitch ( frequency) of howl as that changes the gas density.
  • Gsmith
    Gsmith Member Posts: 420
    Same as the common kid's toy, see https://en.wikipedia.org/wiki/Whirly_tube

    Most likely gas flow velocity related, so changing to larger pipe size may reduce the harmonics to below hearing range.
    ratioayetchvacker
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,542
    edited February 2018
    Think about the non reamed copper pipe that has exhibited localised corrosion and pinholes. Cut open the pipe and see it eroded from the inside due to localised flow turbulence. Well gas is a fluid (not a liquid) as it takes the shape of it's container. Those same velocities and eddies are also happening inside any corrugated fluid path. Think of that white plastic "bathroom fan hose" if you've ever looked inside some used and observed the pattern of where the dust deposited on the down wind side of every corrugatuon.

    Everything about CCST is not good, safety wise and flow wise. That's my conclusion. It's black iron and soft copper for me here in L.P. country.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,169
    @Bob Harper is correct. A flex connector is listed to be used as a flex connector. CSST is not supposed to be used as a flex connector and is not listed as such.
    EzzyT
  • Ironman
    Ironman Member Posts: 7,088
    Let me clarify what I meant: a flex connector is MADE OF corrugated stainless steel tubing even though it's not LISTED as CSST. Therefore, it causes the same harmonic effect as CSST.

    I also understand that CSST is not approved as a field fabricated flex connector.

    My point was that flex connectors cause the same harmonic effect, nothing more or nothing less than that.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Zmanratio
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Ironman said:

    Let me clarify what I meant: a flex connector is MADE OF corrugated stainless steel tubing even though it's not LISTED as CSST. Therefore, it causes the same harmonic effect as CSST.

    I also understand that CSST is not approved as a field fabricated flex connector.

    My point was that flex connectors cause the same harmonic effect, nothing more or nothing less than that.

    I can't recount how many large boilers I've seen with their final gas connections done in CSST... Someone needs to educate the AHJ's....

    ME

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • mstring22
    mstring22 Member Posts: 3
    Two companies here in the Seattle area have poopooed the notion that my foghorning could be due to CSST (nor do they think its a short air intake pipe length, nor drilling a 1/4" hole in the combustion air intake pipe, inside of the boiler vestibule)....but, they also can't figure out the cause. Do any of you all have a recommendation for someone to call in Seattle?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,169
    They are just being lazy. Check "find a contractor" on this site
    GGross
  • Ironman
    Ironman Member Posts: 7,088
    edited January 13
    They “poopooed the notion”, but they have no idea what’s wrong?

    Just think about that for a while.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Solid_Fuel_ManSTEVEusaPA
  • ch4man
    ch4man Member Posts: 288
    edited January 13
    the first time I experienced fog horning, it was a gas designed furnace, don't remember if gravity or belt driven fan but was a gas designed unit from the 50's or early 60's. big SOB maybe 150-200 CFH natural gas.
    I was young and green so one of the old timers came to help. keep in mind this "old guy" (I'm the old guy now) did conversions from mixed gas to natural, probably learned the trade from guys who converted coal furnaces/boilers to manufactured gas, then to mixed.

    anyway as I'm sitting there lost, he walks up to this great big, very loud behemoth fog horning that was rivaled only by a salty on the Great Lakes, and he smiles and gives every primary air shutter a twist and with each one the noise just vanishes........ proper fuel/air.

    just keeping the old stories alive. they help me still to this day.
    GGross
  • mstring22
    mstring22 Member Posts: 3
    I love the stories :)

    Yes, the ~26 year old tech suggested that none of the fixes on this forum (this thread or others) could possibly fix my issue.....

    he was even shocked that adjusting the fuel mixture as high as the manufacturer had recommended (which had reduced the foghorning by ~85%, but not solved it as we still hear it about 4 times a week) could not possibly have had an impact. Bizarre!!

    but he charged $500 and didn't fix it. Ugh.

    Sadly there is no contractor within 100 miles of Seattle. If anyone has a recommendation or is visiting Seattle and is able to look at a foghorn boiler, let me know!

  • Larry Weingarten
    Larry Weingarten Member Posts: 2,788
    Hi, Flexible appliance connectors can make interesting "musical" sounds if you just blow through them. I can imaging @hot_rod making an interesting harmonica with a bunch of different diameter and length flex lines!
    @mstring22 , do you have a flexible connector supplying your boiler? In the west this is commonly done due to earthquake. If you do, simply replacing it with a larger diameter connector could fix things. A photo or two of the setup would be nice!

    Yours, Larry
  • GGross
    GGross Member Posts: 412
    @mstring22

    Can you give me the model of the boiler?

    When was this installed?

    When did the "foghorn" sounds start? (since install, or a period of time after install)

    If possible can you take a picture of the vent termination outside your house while the unit is running?
    mstring22
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,999
    If you were able to adapt different diameters and length to the appliance, then add some solenoid valves, then connect it to a computer program that will alternate the different valves in the proper order, Do you think it might be able to play classical music?
    Edward Young Retired HVAC Contractor & HYDRONICIAN Services first oil burner at age 16 P/T trainer for EH-CC.org
    PC7060
  • Ironman
    Ironman Member Posts: 7,088
    mstring22 said:
    I love the stories :) Yes, the ~26 year old tech suggested that none of the fixes on this forum (this thread or others) could possibly fix my issue..... he was even shocked that adjusting the fuel mixture as high as the manufacturer had recommended (which had reduced the foghorning by ~85%, but not solved it as we still hear it about 4 times a week) could not possibly have had an impact. Bizarre!! but he charged $500 and didn't fix it. Ugh. Sadly there is no contractor within 100 miles of Seattle. If anyone has a recommendation or is visiting Seattle and is able to look at a foghorn boiler, let me know!
    26 years old and he knows more than Tim McElwain who has over 60 years experience with gas appliances? Plus, the other senior techs who agree who have probably hundreds of years combined experience, but this genius thinks we’re wrong and he’s right - but he can’t fix it.

    Proverbs 26:12 KJV
    [12] Seest thou a man wise in his own conceit? there is more hope of a fool than of him.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    STEVEusaPA
  • mstring22
    mstring22 Member Posts: 3
    Can you give me the model of the boiler?
    Its a Lochinvar Knight KHN 110


    When was this installed?
    2017

    When did the "foghorn" sounds start? (since install, or a period of time after install)
    Since install. The frequency reduced by 85% since 2021 when they company turned up the 'richness' of the mixture to the max allowable by the manufacturer.

    If possible can you take a picture of the vent termination outside your house while the unit is running?
    So many pictures attached. Do any of these reveal anything interesting? Could I take any closeups of anything?

















  • GGross
    GGross Member Posts: 412
    @mstring22 personally I would look at the CSST as @Ironman mentioned in the original post. I was checking to see if you may have had recirculation causing a failed venturi, but it seems like your intake/exhaust is separated well, and the rest of the install looks pretty good
  • ch4man
    ch4man Member Posts: 288
    edited January 26
    looking at the CA print out, your still running awful lean. now I haven't looked at your boilers requirement but I can't recall one condensing boiler that states that low of CO2 or O2 that high as being ok.
  • jpm659er
    jpm659er Member Posts: 16
    Ch4man is right. Running lean. Definitely not to the max richness that manufacturer calls for.
    I find they tend to run more lean at low fire though. What was the firing rate when tested? Also, at what firing rate does it make noise?