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Am I having issues with my chimney and exhaust gases in my home?

blockiert
blockiert Member Posts: 4
I have a 5 ton gas-fired furnace in my basement. Initially the house was probably built with a smaller unit, but they built out a large basement and added a stronger furnace. Anyways. It shares the exhaust with two gas-fired boilers. The chimney or exhaust pipe goes right through the floor of the ground floor, through the attic and exits above the roof.

Now, on the first floor the chimney is surrounded by drywall but around the drywall that encapsules the chimney on the ground floor, there´s a weird somewhat smoky smell sometimes. It´s noticable. I am wondering if this can be caused by the chimney. Maybe it´s leaking. Maybe it´s not and it´s just coincidence that the chimney goes right through where the smells come from.

I bought a carbon monoxide detector with a digital display, but that stays on 0 all the time. I am not sure what this tells me.

Question 1: Is there any better way to tell if the smells are actually exhaust gases or not?

Question 2: The way the exhaust from the furnace and the two exhausts from the hot water boilers all lead into one chimney looks a little bit strange... Is it possible that there´s backdraft and this goes left and right of the chimney upwards? But even then I wonder how I could get to the bottom of it.

Thankful for every idea someone might have!

Comments

  • Big Ed_4
    Big Ed_4 Member Posts: 2,697
    What is the total BTU input of all the appliances connected to the chimney ? What is the diameter size and hight of the chimney ? Any long horizontal runs to the chimney ?
    I have enough experience to know , that I dont know it all
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    Can you post a photograph of the three appliances that vent into the chimney? It sounds like you have a B-vent manufactured venting system. This type of venting system is common in many homes built from the 1970s thru to the present. Less now though because of the more efficient plastic venting systems available. There are rules to the amount of BTU input for a particular size B-vent. If you have a vent that is too small, the exhaust gasses may spill out into the room where the gas appliances are located, then travel up inside the home to the place where you are "Smelling" them... Carbon Monoxide (CO) is odorless and colorless so you are not smelling that, but you may be smelling other byproducts of combustion or perhaps construction material like wood or sheetrock that is overheating. You should get that looked at by a professional based on what you have posted so far.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • blockiert
    blockiert Member Posts: 4
    So, the two boilers are at 38,000 BTU each and have each a 4in pipe for exhaust that then meets a 6in pipe that goes probably 4-5 ft in the basement, 9-10ft through the groundfloor and probably 10-12ft through the attic, so 23 to 27ft in total. So, with the furnace I think in total 136,000 BTU go through this.

    I dont know what qualifies as a long horizontal run, but it looks like this:



  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    edited February 5
    One of your boilers is a water heater. is the other boiler identical? Those appliances are not fan assisted vents and can be vented in a CAT I vent like the B-Vent that you have. The furnace may be a Fan assisted vent but still a CAT I appliance. There are venting tables that will indicate if the 6" B-Vent is the correct size.



    It has been some time since I needed to select vent sizes but I believe your vent system is sized correctly.

    This is table 4. from the GAMA sizing guide. In the Green box is the single wall connector sizes and your appliances fit within the maximum capacity of a 4" connector The total of all the appliances does not exceed the max in the Yellow box for the vent you described.

    When you can't find the exact numbers you are to interpolate the number that would be between the numbers that are shown on the chart.

    If all three appliances were to operate simultaneously the total BTU venting in the common pipe would be 136,000 BTUh. That is less than the 260,000ish maximum for 6" B-Vent, 25 Feet tall

    Each of the 4" connectors is within the maximum for NAT (not fan assisted) and the furnace is about 98,000 which is within the Min and Max for that 4" vent connector.

    So the venting is correct, What you fear is that the vent may be disconnected behind a wall and could be letting exhaust gasses into your home. If you have that concern, then I would call o professional to have that inspected and repaired if it is defective in any way.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    Bob Harper
  • blockiert
    blockiert Member Posts: 4
    This is very helpful and tells me at least there isnt anything obviously wrong with the design of the system. That´s good to know already.

    So, this 6in B-Vent tube that goes from the basement through the ground floor level through the attic and eventually through the roof, is this usually one piece? Or is there a standard length where this is pieced together of? Like 8ft or 16ft or... something like that?
  • Big Ed_4
    Big Ed_4 Member Posts: 2,697
    A exhaust fan can effect the draft..
    I have enough experience to know , that I dont know it all
  • yellowdog
    yellowdog Member Posts: 146
    @blockiert Its probably only 3 or 4 foot sections twisted together.
  • blockiert
    blockiert Member Posts: 4
    Could these sections in theory become loose? E.g. because the furnace is vibrating or shaking? @yellowdog
  • RickDelta
    RickDelta Member Posts: 179
    edited February 6
    I'm no Pro ......
    But I don't care for that horizontal run as it actually looks to be sloping backwards! I would like to see it tilted up as not to allow any residual exhausts a place to reside.

    ....... also I would silver tape (High temp) all those joints.


    I'm guessing the water heater is 3" exhaust out and immediately transitions up to 6" to enjoin the other trunked exhaust ??

    I'd be concerned that if is producing a non-laminar pipe draft (resulting in poor drafting or back spillage)
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,563
    blockiert said:

    This is very helpful and tells me at least there isnt anything obviously wrong with the design of the system. That´s good to know already.

    So, this 6in B-Vent tube that goes from the basement through the ground floor level through the attic and eventually through the roof, is this usually one piece? Or is there a standard length where this is pieced together? Like 8ft or 16ft or... something like that?

    The standard B Vent sections come in 6" Diameter x 6" long, 12" long, 18" long, 24" long, 36" long 48" long, and 60" long. There is also an adjustable piece that can slide from about 10" long to 18" long if you need a custom length and adjustable elbow that can be twisted from 90° to straight, as needed. Each section of pipe has a male end and a female end. they usually twist together and lock. Some just snap together. So in your 20+ foot manufactured B Vent chimney you probably have at least three 60" sections and some other pieces to make it through the roof.

    There is a possibility that there is a defective connection behind the wall. A chimney sweep can check that out for you.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Bob Harper
    Bob Harper Member Posts: 1,030
    The vent connector must slope 1/4"/ LF up towards the chimney. The connector must be properly supported. Three screws per joint equidistantly spaced. Foil tape or any covering specifically prohibited by code and unnecessary. Many of those TEK screws failed to penetrate the inner section resulting in daisy petaling it in. If anything encroached into the stated 1" clearance to combustibles they could be the source of odors. If need be, open the walls and inspect the firestops. Get a low level unlisted CO monitor. Have a pro run combustion analysis on each appliance.
    Big Ed_4realliveplumber
  • RickDelta
    RickDelta Member Posts: 179

    The vent connector must slope 1/4"/ LF up towards the chimney. The connector must be properly supported. Three screws per joint equidistantly spaced. Foil tape or any covering specifically prohibited by code and unnecessary. Many of those TEK screws failed to penetrate the inner section resulting in daisy petaling it in. If anything encroached into the stated 1" clearance to combustibles they could be the source of odors. If need be, open the walls and inspect the firestops. Get a low level unlisted CO monitor. Have a pro run combustion analysis on each appliance.

    Is High Temperature Flue Tape not code approved ??
  • Big Ed_4
    Big Ed_4 Member Posts: 2,697
    There was some issues with the glue used on the tape ... The tape was first used to fix bullet holes in wings.....
    I have enough experience to know , that I dont know it all
  • realliveplumber
    realliveplumber Member Posts: 350
    RickDelta said:

    The vent connector must slope 1/4"/ LF up towards the chimney. The connector must be properly supported. Three screws per joint equidistantly spaced. Foil tape or any covering specifically prohibited by code and unnecessary. Many of those TEK screws failed to penetrate the inner section resulting in daisy petaling it in. If anything encroached into the stated 1" clearance to combustibles they could be the source of odors. If need be, open the walls and inspect the firestops. Get a low level unlisted CO monitor. Have a pro run combustion analysis on each appliance.

    Is High Temperature Flue Tape not code approved ??
    There is no tape that is approved.
  • Bob Harper
    Bob Harper Member Posts: 1,030
    There is no such thing as 'high temperature flue tape' and no, NFPA 211 expressly forbids covering vent connectors with ANYTHING. What is your purpose for wrapping connector joints? Curious.
    realliveplumber