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Flue Sizing Question

Howie718
Howie718 Member Posts: 14
Hello All,

Back in Feb I posted a question on finding a pro that works on fabricated chimneys. I found an outfit through the CSIA website and they performed a level 2 inspection which revealed that the b-vent should be replaced. The current vent is 8 inches and they are proposing 6 inches for the new one.

The boiler is a 3 year old peerless at 175k btu and the water heater is also 3 years old at 75k btu. The height is 30-35 feet. They also suggested using a 6 inch liner inside the existing 8 inch b-vent, but only if the building dept in my town would allow that.

Any feedback would be helpful.

Thank you, Howie

Comments

  • Howie718
    Howie718 Member Posts: 14
    I should have added, both the hot water heater and the boiler are natural draft and both are gas fired.

    Thank you, Howie
  • ChrisJ
    ChrisJ Member Posts: 13,883
    edited August 2022
    I'm not a pro.

    But.
    Pulling a liner inside of an old B-vent? I highly doubt any liner is approved for that.

    Here's a chart from Hart & Cooley for their B vent capacities using multiple appliances on one vent.
    The height of the B vent is important as is how far the horizontal run is. You'll be using the "NAT" column for natural draft.

    From what I see a 6" isn't going to cut it.




    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Howie718
    Howie718 Member Posts: 14
    @ChrisJ , thank you. I am calling my building dept on the liner question. Just curious, in that catalog, what is the difference between the tables 4 and tables 5? Also the difference between table a and b for both? When I look at table 4a it looks like a 8 inch is needed but on table 4b a 7 inch.....unless I am totally reading these wrong....which is most likely :)

    Thank you, Howie
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    I see no reason to restrict the liner inside the "B" vent as it acts as an insulator to keep the flue warm.

    But the sizing seems to be in question. At over 30 feet a 7" B vent will work if you have 3' connector height which you may or may not have. *" B vent which you have seems like the right choice.

    Liners are usually corriguated which restricts the flow to size for size they must be upsized
  • Howie718
    Howie718 Member Posts: 14
    @EBEBRATT-Ed , thank you. So now I have to discuss sizing and make this guy feel like the homeowner is stepping on his toes.....awesome. Or I just walk away and find someone else. Its been a chore to find chimney professionals that work on fabricated b-vent systems.
  • pecmsg
    pecmsg Member Posts: 3,555
    Venting I won’t comment on. 
    175K is a lot of hot water?
  • Bob Harper
    Bob Harper Member Posts: 955
    You need 7" at min. so just keep the 8" and forget about liners in B-vent. None are listed for this. The chart posted above is for vent connectors. You need to look at the chart for the common vent. You need to know whether you'll be using B-vent or single walled connector and if the vent is straight up or with offsets.
  • captainco
    captainco Member Posts: 736
    If your B-vent needs to be replaced it sounds like you have some venting issues. Bob is right that 7" would be minimum but minimum might not be the best solution. Whatever you do I recommend someone that knows how to do proper combustion and draft testing check it all out when it is done. A little big is better than a little small!!
    Bob HarperEdTheHeaterMan
  • Howie718
    Howie718 Member Posts: 14
    Thank you everyone. It sounds like I need to get a second opinion. It has been tough finding chimney people that work on these. They would rather do masonry chimney work.

    @captainco , would it be the chimney people that perform the combustion and draft test or is that someone else?

    Thank you, Howie
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    @Howie718

    You need and HVAC tech that knows combustion. Certified chimney sweeps usually install liners and probably B vent as well so you may search for one. Typically, HVAC, Plumbers, heating techs also do this. It probably varies depending on what part of the country you're in. A company that installs fireplace inserts, wood stoves or gas logs is another place to try.

    Try finding a wholesale supply house in your area that sells liners and B vent. Call around and ask them if they have any recommendations. They sell the stuff and will know who the installers are.

    If that fails call a MFG of B vent like Hart & Cooley or Amerivent they will know who buys B vent in your area
  • Howie718
    Howie718 Member Posts: 14
    Thank you all. The reason they are recommending replacing is not because of rot or corrosion. He lists it as a "breach", but he was unable to really confirm if the bvent was damaged, so he is recommending replacing. I've asked for the photos of the inspection which he agreed to send me. I will post them for you guys. When I looked at the image on his camera, to me it looked like the inner wall got wrinkled up when it was installed...so it is possible it has been like that for 25+ years.

    The only reason I did this was because of the leaking chase cover.
  • Howie718
    Howie718 Member Posts: 14
    All, here is the photo of the interior of the b-vent. His reaction was **** is that and he didn't want to send the camera up any further.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    It could be completely fine. I would look for a certified chimney sweep to drop a camera down and give you an honest opinion. It may have been installed that way or a gust of wind may have blown the b vent sideways causing the wrinkle
  • captainco
    captainco Member Posts: 736
    I believe EBEBRATT-Ed covered it all. Chimneys sweeps don't usually do combustion testing, unless Bob Harper knows a few.
  • Howie718
    Howie718 Member Posts: 14
    @EBEBRATT-Ed and @captainco , but that is what I had done. I found a certified chimney sweep from the CSIA.org website and he snaked a camera into the flue servicing the boiler. He disconnected the vent in the basement and snaked the camera up through the b-vent. That image is the interior of the b-vent. I am confused, so sorry. Thank you, Howie
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    should have sent the camera to the problem to get a clearer picture of what happened
  • ChrisJ
    ChrisJ Member Posts: 13,883
    That picture looks pretty clear.
    The inner liner isn't intact. It's damaged.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Howie718
    Howie718 Member Posts: 14
    My last question for you all.....can someone recommend a chimney/venting company so I can get both a second opinion and a second estimate? I am in Bergen County NJ. Thank you and have a great holiday weekend. Your input has been greatly appreciated.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,127
    @Howie718

    Maybe if you pm @EzzyT or @clammy they could recommend someone
  • EzzyT
    EzzyT Member Posts: 1,220
    @Howie718 PM and I can send you the contact info of good quality chimney companies 
    DJD775MikeAmann