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Knight Boiler foghorn

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JBW_2
JBW_2 Member Posts: 67
GoCat,

My issue was different. Totally unrelated to exhaust. But the noise sounds very similar. My noise was caused by a vibration within the machine and could be stopped by either adjusting combustion product percentages or placing a shim between heat exchanger and fan.

Thanks for keeping us posted. This is great stuff.

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  • GoCat
    GoCat Member Posts: 12
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    Knight Boiler Foghorn

    In hopes that someone in this group can help: I have a Lochinvar Knight KBN080 for radiant floor. Problem is this: When starting up, something in the unit sounds like a foghorn. Or, maybe like the sound you get when blowing air across a beer bottle. The intensity is (I think) related to the burn rate -- starts out high, and then settles down.

    It's a bit annoying -- can hear it throughout the house.

    It's a new install; it's a weekend, so hard to get hold of anyone. Thought I'd ask here.

    Anyone ever run into this? Know about it? Have an idea to fix?
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    What are your..

    CO and CO2 readings? Gas pressure coming into the boiler
    both static and running? Is the boiler Nat. gas or L.P. ?
    Is this sound only on fire-up? What is the vent length, how is it vented, vertically or horizontally?
    Lots of questions... -Greg
  • GoCat
    GoCat Member Posts: 12
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    Must admit...

    ... that I am not a Pro. (Ducks for cover.) So, here's what I know:

    Gas pressure was checked by gas company, found to be within spec of the boiler. This was static, and I don't have the number. It's natural gas. I do not have the combustion gas readings, yet -- am hoping to call a HVAC guy once my installation is done. I guess I didn't consider it "done" with this noise happening! Maybe I'll get that giong sooner, eh?

    Vent is horizontal, using the concentric vent kit. That horizontal run was shortened, it's about 28 inches, total.

    From the back of the boiler, very short extensions (about 6") to the concentric Y adapter, then the other end of the Y, through the wall. Total from the coupling at the back of the boiler to the termination is 28 inch.

    So... I will get the gas analyzed. And thanks in advance for any other suggestions.
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    GoCat...

    The Min. Vent length for a Kight is 12 feet, you add five feet for every elbow however. It may just be vent length.
    I would do a combustion test and also bring a monometer
    to the job, as soon as possible. Let us know what you find. -Greg
  • GoCat
    GoCat Member Posts: 12
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    Min length, who woulda known...

    Greg, thanks for the thoughts. I will get the tests done as soon as possible.

    But, I'm disappointed to learn of the 12 foot minimum vent length. I've scoured the installation manual, and see no mention of this, just the maximum length. In fact, in the instructions for using the concentric kit, it says the length of the kit may be made as short as possible -- although it doesn't indicate any length requirements between the kit and the pointer.

    Well, I won't do anything until I get the testing done. If it is the venting (and I suspect it is, just based on the sound), then I can go off to a different wall.

    By the way, I realized I forgot to answer one of your questions: Yes, the sounds only comes during startup. Sort of a WOOOOO..... WOOOOOO..... WOOOOOO.... effect; then a longer WOOO, then it stops. Overall it doesn't last more the maybe 15 to 30 seconds. Weird, I think.
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    Page #8

    of the I&O manual, you can also go online and get it.
    www.lochinvar.com
    Bring a little more pipe w/ you as well as a few 90's...
    remember 90's = 5 feet. Good luck. -Greg




  • GoCat
    GoCat Member Posts: 12
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    Page 16, actually

    Greg, this is great. First, thanks again. My I&O manual (came with the unit) is dated on the back as 05/07, Revision 6. There is truly no mention of a minimum vent length. So, got online, and the latest is Revision 8, 10/07. Sure enough page 16 says:

    Minimum / Maximum allowable combustion air and vent piping lengths are as follows:
    Combustion Air = 12 equivalent feet minimum / 100 equivalent feet maximum
    Vent = 12 equivalent feet minimum / 100 equivalent feet
    maximum.

    In my (slightly older) manual the same section on page 16 reads:

    Maximum allowable combustion air and vent piping lengths are as follows:
    Combustion Air = 100 equivalent feet
    Vent = 100 equivalent feet

    No mention of minimums! Well, at least I don't feel TOO stupid. Just annoyed. I really do try and do things "by the book", but if the book is incomplete, well... what can I do?

    So, let's see... Four 90 degree elbows, butted right up to each other makes 20 feet. That's gonna look really goofy!
  • hot_rod
    hot_rod Member Posts: 22,158
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    I'd try to adjust

    the gas valve first. With factory support on the phone you may be able to make the noise go away. I have a few installed with less pipe then suggested. No noise. Worth a try.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GoCat
    GoCat Member Posts: 12
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    Concentric vent did it

    Just a quick update on my mystery noise. Took the suggestion of adding pipe length -- two elbows (equals 10 ft) plus 3 ft straight plus the concentric vent kit (manual says that's another 3 ft.) Sadly, no help.

    But, I did notice that if I remove the concentric kit, then the noise goes away. In fact even if I remove just the center pipe (exhaust) from the kit, the noise is gone.

    Now, I'm thinking I must not use the concentric kit. Why did I buy it at all you ask? Simply this; The I&O manual shows that it can be installed with less clearance under a roof or overhang (12 inch min), as apposed to the separate pipes (5 feet). The side of the house that would be most unobtrusive for the vent, and is closest to the boiler, has a pushed-out bay window area above, and that kills the 5 foot requirement. So, now I'll pipe about 14 feet to the other wall, and ask my wife to try and do some clever landscaping to hide it from view.

    Why am I writing all this? two reasons; First to let folks know what I've learned so far. Second, just in case someone comes back with "oh, hey, all you gotta do is..."

    Besides, this is a cool forum! :-)
  • hot_rod
    hot_rod Member Posts: 22,158
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    But still...

    get someone to put a combustion analyzer on 'er and dial it it.

    It's rare to find one adjusted perfectly from the factory. Lean or rich mixtures are not going to be kind to the burner and HX in that nice piece of expensive equipment.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    dialed in?

    If the numbers are within the factory specs, is there an optimal "dialed in" that we want to see? My nice piece of expensive equipment and I would like to know!

    Thanks

    Larry
  • JBW_2
    JBW_2 Member Posts: 67
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    Noisy Knioght

    Hey Chief,

    Had the EXACT same problem with my knight 150 about 3 weeks back.

    Also, as a test, completely disconnect your exhaust and air intake lines from the boiler and fire it up. If there is still the noise (and the things sure as hell sounds like a foghorn) then a quick and easy bandaid, is to jam some sort of shim between the heat exchanger and the fan. I recommend contacting Lochinvar. They were great with regards to customer service. I am in the middle of dealing with them regarding this issue.

    Regards,

    Josh W
  • JBW_2
    JBW_2 Member Posts: 67
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    noisy knight

    Hey Chief,

    Had the EXACT same problem with my knight 150 about 3 weeks back.

    Also, as a test, completely disconnect your exhaust and air intake lines from the boiler and fire it up. If there is still the noise (and the things sure as hell sounds like a foghorn) then a quick and easy bandaid, is to jam some sort of shim between the heat exchanger and the fan. I recommend contacting Lochinvar. They were great with regards to customer service. I am in the middle of dealing with them regarding this issue.

    Regards,

    Josh W
  • Ted_9
    Ted_9 Member Posts: 1,718
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    Boiler

    I'd also look at what kind of gas piping and the size of it. Does this only happen when in low fire?
  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    Ditto Ted

    are you using Ward Flex or some type of flex going into the boiler? I have seen MANY brands of boilers in the past w/ the same noise...and the "foghorn" was coming from the gas pipe. If it is flex, try moving it around (back and forth) during fire-up. You should do a combustion test soon. -Greg
  • GoCat
    GoCat Member Posts: 12
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    update

    Josh: Disconnecting the exhaust pipes removes the noise. Actually, just removing the center pipe from the concentric kit removes the noise.

    Regarding the gas piping: Used 3/4 pipe all the way (about 7 feet from the 1" line, which is about 4 feet from the main 1-1/2 line) to a 3/4 valve, then the flex hose, then a reducer 3/4 to 1/2 to mate to the boiler's inlet pipe. Is that reasonable? (Before you ask, the 1" line also feeds a tankless, but I've made sure it's not firing when I was hearing the noise. The only other gas appliances in the house are dryer and stovetop.)

    I will definitely try moving the flex a bit.

    Combustion analysis is coming soon! (Hopefully this afternoon, local outfit is trying to schedule me in.) I'll post a note once I have that done.

    Also, now that it's Monday, I've talked to the very nice folks at Lochinvar, and am looking forward to resolving all this soon with their help. Stay tuned!
  • GoCat
    GoCat Member Posts: 12
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    Latest news...

    Had a local HVAC guy come to do the measurements. We thought we'd start by double-checking gas supply pressure. Guess what? He discovered that the gas meter's regulator diaphram is leaking a bit. "Sucking air" is how he described it.

    No idea if this is related to the foghorn -- although we hope it may be that the gas supply pressure builds up too high when boiler is off, then the foghorn sounds at startup until the pressure gets back to the right range. Nice theory; we'll see. In the meantime, no point in doing the exhaust gas analysis until it's fixed.

    Gas company is slow. Not until Thursday, they said.

  • Greg Gibbs
    Greg Gibbs Member Posts: 75
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    Let us

    know... -Greg
  • k_log
    k_log Member Posts: 1
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    Noisy Knight


    Josh

    What's the delta T when the unit is stable on high-fire ?

    I've seen some look-alike issues with Knights caused by a low flow. The pump is supplied with this unit but if your piping is too long or too restrictive you can have this kind of problem. Per example, if you have a Grundfos UPS26-99 on a 500MBH Knight, and you put it on the low speed, it will do exactly the same thing.
  • JBW_2
    JBW_2 Member Posts: 67
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    noisy knight

    I'm at 30-35 deg F on high fire.
    I do have a very short boiler loop, though.
    I could try to change that and see if it makes a difference

    JBW
  • GoCat
    GoCat Member Posts: 12
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    Monday Update

    Has anyone ever noticed that everything takes longer than planned??? Indeed....

    OK, so we left our intrepid hero waiting for a service call from the local gas company, having been told that the meter was busted. Not so, says the gas man! Indeed, it seems the HVAC tech had cranked the meter regulator TOO low, which was causing it to behave badly. Why did he do this? I don't know. It was just under 5 inches (lockup) when gas man came out. So, gas man left the gas pressure at 7.5 inches running, just under 8 lockup.

    Finally, HVAC tech made it out again this morning. At this point, I had him stay focused on the one task: Get the flue gas readings! They all appear to be right in range for this boiler. (O2=5.2%, CO2=8.9%, CO=96ppm).

    So, the upshot is, I really have no useful information about the foghorn. Unfortunately, I have to attend to my real job today (I'm actually a retired spirit, trapped in a working man's body), so in a day or two I'll reconnect the concentric kit and continue to work this mystery noise.
This discussion has been closed.