Noisy Type B Vent

[RetiredGasMan]

I am in the process of replacing builder grade 80% natural gas York furnaces and 10 SEER a/c units in my 3 story, 5000 sq. ft. 12 year old house in Virginia. House has 2 zones with a furnaces in basement and attic. Replacing systems with Carrier Infinity Hybrid system with 80% plus variable speed furnaces and multi-speed 16 SEER Infinity heat pumps. Will use Infinity Controller. The basement unit vents through a chase to the attic and since the house was new we have experienced an annoying crackling sound on cool-down from the 6" Hart & Cooley B-vent. As we're nearing completion of the installation of this high tech system I'm thinking I should finally address this noise as well. Hart & Cooley was of little help other than discussing the obvious stuff like improperly installed sheet metal screws which we have none of. Of course the vent pipe is behind drywall 95% of the run and passes near the master bedroom. I got a bid from our contractor to replace the B-vent while on-site and I nearly fainted so I'm considering addressing the issue myself (I'm very handy) once they're gone. I can get access to the beginning and the end of the B-vent without cutting drywall but in order to remove and replace the entire vent run (probably 20+ feet) I would have to cut a lot of drywall. I am going to try to reinforce the basement end of the B-vent to see if that helps but I'm also thinking about sliding preformed mineral wool pipe insulation down from the attic and up from the basement around the B vent (I know they like 1" separation from combustibles) to insulate the noise. Has anyone ever tried this? Any other thoughts or experience with noisy B-vent? Thanks in advance.

[beenthere]

Never done it.

Are you sure the noise wasn't fromyour old system being oversized, and over heating the B vent.
And now with the new smaller BTU sized units. You won't have the noise anymore.

[RetiredGasMan]

Thanks Beenthere for quick response. I am not sure if it's been overheated... it's a good question. I do know that it crackles also when just the water heater is operating, again on cool down only, and the water heater shares a vent with the basement furnace. I'd guess the flue gas temperature on the water heater is less than the furnace but that's a shear guess. The new Carrier basement furnace will be operational on Thursday so I'll let you know whether that makes any difference. The purpose of trying the pipe insulation was just to kill the noise bouncing in the chase.

[beenthere]

Yea, the water heater won't heat it up as much as the furnace.

So, its probably a less then proper install.

[hearthman]

Insulate around the B-vent, you void the warranty and listing and could cause a fire. The problem with insulation is, it works. It keeps hot things hot instead of allowing ambient air (the 1" air space) to cool the pipe and surrounding combustibles.

You may have noise from the appliances themselves telegraphing up the vent or you could have something in the chase such as a homemade firestop rubbing against the vent. I recommend you open the walls and perform a Level III inspection.
HTH

[RetiredGasMan]

Thanks Hearthman. The reason I specified mineral wool as opposed to fiberglass insulation is that, I believe, it is classified as a "non combustible". I think it is the same stuff they wrap high pressure, high temperature steam lines with in industrial applications. From what I can tell it is also an excellent sound deadner. But, with all that said, I'm still very much leaving open your solution. I just hate doing drywall work! From what I can see there is no question that the original installing contractor used homemade firestops. There's 3 in the run and I can get to 2 of them without opening the chase. If I open it up I'll just replace everything to be safe and insulate the interior walls (maintaining the 1" clearance from the B-vent) of the chase to kill any residual noise. Thanks again.

[m kilgore]

I recall having a problem with a noisy flue 20+ years ago. I can't recall the brand but the manufacturer ended up comming to the house and having us replace the pipe on their dime. Then they wanted the old one back to inspect what was causing the noise. Ended up being somthing on there end and not a bad install. It was a noise like you describe and very loud. It would wake up the homeowners at night.

I would recommend having the flue replaced and not trying to slide insulation over it.

[RetiredGasMan]

Thank you M Kilgore. The more I think about the insulation option the more I realize that once I've opened the system up enough to slide on insulation I probably can replace the B-vent with some additional work. Might as well do it right. This noise is definitely the sound of metal against metal expanding and contracting at different rates but interestingly the crackling only occurs on cool-down. While I can't see the B-vent inside the chase I can approximate where the connections are between sections and when I put my ear to the drywall at that location it sounds as if several connections are making the noise. Thanks again.

[rojacman]

[ is it possible that the temp in the area that the pipe is in a cold area causing excessive expansion & contraction? Also i had a heating 6" rd. in a cool basement where the installers put hangers in but screwed the pipe tight to the hangers not letting the pipe move & creaking keeping people up at nite. removed all the screws & a week later they sent me a 50.oo gift cert to a good restaurant for quieting down their noise. ya gotta win once in a while. mabe the pipe is anchored too tight ?????. good luck.........Jack

[the dangling wrangler]

Maybe I missed something. Why is the pipe 6"?

[bkcalhoun]

Yea, the water heater won't heat it up as much as the furnace.

Really? I have measured flue temps in excess of 600* with the new flame arrester water heaters, and 80% furnaces typically run around 400*

[bobRitchie]

Fire Hazard

My B-vent was packed tight with cellulose insulation due to stupid
insulation contractors putting in additional attic insulation. I openned
the whole thing up and replaced it, because the HVAC contractors and
plumbers had hacked it up in the basement, and it was 40 years old.

I think its a Very Bad Idea to have any insulation around the B vent.

Working with the B vent is easy, the only issue as you guess is fixing all
the drywall.

There are numerous brands of incompatible B-vent, particularly for the oval
stuff which I have. Make sure you can get your hands on all the right fittings
before you start the project. You don't want to hack it like the HVAC guys and
plumbers did to me. Home Depot can order the Amerivent stuff. However I had
to order multiple quantities, like 4 of several fitting I only needed one of.

There was a episode of "Finders Fixers" on the old Discovery home channel with
exactly this noise problem. If I remember correctly they found that the pipe sections
were touching 2x4 framing in the wall. They fixed the noise just by properly
installing new B-vent.

If your furnace is not firing hot enough you might get a build up of white residue
inside the B-vent. We are in deep DIY territory here, but if you have white residue
on the inside of the B-vent have your HVAC guy look at your gas pressure on the
valve. Since you are getting new units make sure they are set up properly.

[bobRitchie]

Get a contractor to replace your B-vent!


But the Home Channel did do a show where exactly the kind of noise
you had was solved by replacing the B-Vent. Because the B-vent
was touching framing in the walls. Do not use this for DIY - just to
see that this can be the issue.

Links to diy not allowed

[bobRitchie]

Very Dangerous Situation

The sounds you are getting may be from condensation inside your walls!
See the link I put in the last post.

If this vent is near the bedroom you may wake up dead. There are
likely flue gasses in your walls.

I would not have posted a DIY link - but it shows the danger.

[beenthere]

Really? I have measured flue temps in excess of 600* with the new flame arrester water heaters, and 80% furnaces typically run around 400*
A 40,000 BTU 80% water heater with a 600° stack temp, doesn't put as much heat in to the chimney as a 100,000 BTU 80% furnace at 400°.

If it is. Its a lot less then 80% efficient.

[RetiredGasMan]

Thanks Rojacman. The chase is in the interior of the house with the attic penetration being insulated and the basement drop above the furnace and water heater being into heated space so I'm guessing there's not a significant temperature differential. The run is completely straight and vertical. On the very small section I can see it is supported by hangers fashioned out of duct work drives. The run may be supported at a firestop I can't see (yet) but clearly there is no play whatsoever vertically in the run. Don't know if that's good or bad?

[RetiredGasMan]

Dangling Wrangler.... it's what the original HVAC contractor put in the house. I went to Hart & Cooley's sizing literature online and confirmed the sizing was correct based on the appliances' BTU ratings and the run length.

[RetiredGasMan]

Thanks bobRitchie for your posts. Based on all the much appreciated feedback I've received here I will eliminate the pipe insulation option and only consider B-vent replacement or re-support options. I'll check that link out. I guess there are worse things then repairing drywall!

[rojacman]

Maybe I missed something. Why is the pipe 6"?hi wrangler , i was just referring to a repair i did on a 6" heating run in a cool basement that was fastened down too tight & made noise when heated . When i loosened the hangers the noise stopped . i was using that example as a possible explanation to what his problem is........Jack

[the dangling wrangler]

hi wrangler , i was just referring to a repair i did on a 6" heating run in a cool basement that was fastened down too tight & made noise when heated . When i loosened the hangers the noise stopped . i was using that example as a possible explanation to what his problem is........Jack

I understand that. I was thinking 6" is kinda big pipe but, not knowing what other appliances were venting into this run, it's hard to make an informed opinion.