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  1. #1

    Furnace vent touching new wall

    We've just had a contractor build a new wall in our basement, to enclose the hot water tank and brand new gas furnace (York).

    We had to call a furnace repairman to replace the overheat switch, due to all the drywall dust that clogged up the system.

    While he was fixing and cleaning the furnace, he pointed out that the single-size vent (I don't know what it's really called) is a serious fire hazard because it's going through the new wall (it looks like it was cut out with a butter knife - not very attractive). Everything I've read so far talks about having a B-vent go through a wall with a 1" buffer, but doesn't even mention the single vent size.

    When I mentioned this to our contractor, who has 29 years experience, he said he has never heard of that and had no idea what I was talking about.

    Can anyone give me more understanding of this issue so I can make sure the job is finished safely? If our contractor, who we trust to know this type of thing, doesn't know it, I want to make sure I'm super clear on it and that the furnace guy wasn't just trying to earn himself some new business (my gut tells me he's actually the one who is right).

    The furnace repairman didn't mention how close the wall was to the big fat vent (I think it's the air intake vent), so hopefully that means it's OK, but would appreciate any comments on that, too. Thanx so much!

    Here is a link to the pics.

  2. #2
    Join Date
    Dec 2007
    Posts
    4,710
    so you trust a drywall person to know the codes for venting an appliance and when you get information from the HVAC guy you question that??!!

    single wall vent pipe, one thin layer of metal, needs 6" ( if memory serves me ) of clearance to combustibles where as B-vent only requires 1" clearance.

    If your drywall guy did the hole for this, I would question the 29 years experience!!

    most furnaces have specifics on how close things can be printed on the information label inside the upper door of the unit as well as in the instruction manual.

    there is a minimum requirement for combustion air that needs to be considered as well. call that HVAC guy back if you cannot find the information, seems he has your best interest in mind!!

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,123
    As above. Single wall needs a large clearance from combustable material.
    B vent, needs less, and is safer for penetrations through combustable walls/materials.
    A thimble is used to provide the air gap that B vent needs.

    Contact your service/repair guy again, and have him come and take care of it.
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  4. #4
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,586
    Do not use the heat till it is repaired to code!
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  5. #5
    Join Date
    Sep 2005
    Location
    central jersey
    Posts
    289
    I agree with the above,either cut the hole bigger or install b vent

  6. #6
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,197

    Exclamation

    You need B-vent to penetrate that partition using a listed wall penetration. That ceiling firestop looks homemade so it would need to be listed as well. You should use the same brand B-vent as the vertical stack. The horizontal run is not properly supported. Enclosing that room makes it a "confined space". You need 50 cubic feet of room per 1,000 BTU/hr input rating of all combined appliances.

    Both contractors leave a bit to be desired in my book.

    Your overheat trip may have been from a lack of makeup air and not just drywall dust. Also, how did all that dust get in there? Ducts not sealed? Code requires ducts to be sealed within 10 ft. of the plenum. Now you will probably need to have your ducts cleaned.

  7. #7
    Join Date
    Feb 2009
    Posts
    131
    we use double wall vent pipe on all gas furnaces. It requires a one inch space between all combustibles. I ALWAYS make sure my installers leave atleast 2" just to be safe.

  8. #8
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,562
    Double wall flue pipe needs 1" of space. Not sure of single wall flue pipe, against code in my area to use. You also have a picture of PVC pipe, that doesn't need any clearance. If you're general contractor has never heard of such a code, I would be a bit scared of the quality of work he has done in other areas. Any builders we work with know that one.
    I like DIY'ers. They pay better to fix.

  9. #9
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    That's not PVC pipe. It's a single wall vent connector (painted white) that's connected to a type B common vent. Your clearances are not allowable with single wall pipe. The single wall should be replaced with B vent.

    Also as has been said, be positively sure that there is adequate combustion air openings.
    There is nothing more frightful than ignorance in action....Mark Twain

  10. #10
    Join Date
    Jan 2006
    Location
    Powell River, BC, Canada
    Posts
    763
    6" clearance for single wall (c-vent), 1" for double wall (b-vent). bmatherws- that's c-vent pipe that's been painted! That penetration IS a fire hazard! Have it corrected right away! Also make sure the combustion and ventilation air requirements are met for enclosed spaces. The door should have louvered grilles top and bottom to allow the space to communicate to the rest of the space for ventilation air. Did your contractor check for proper clearances to the equipment for servicing? Was thought put in to replacing the equipment when needed? Is there enough room to disconnect the ductwok etc. ?

    This is one of my pet peeves. The equipment is installed in an open space, and then later closed in such as this without any consideration to these issues. I looked at one a couple of weeks ago that had a leaking HWT. The doorway had to be opened up and the furnace and some of the ductwork had to be removed to do it. What should have been a 2 hr. job turned into 8+ hours and big $$$. Ended up having to make a new plenum adapter as the old one had to be cut out because there was alot of screws in the rear and side that were no longer accessable.
    Where are you? Are you done yet? I got ONE more call for you.....

  11. #11
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,562
    You're right. It's metal. That's some shiny ass metal. My powers of observation scare me sometimes. At any rate, it isn't safe as it is. Ductboard is a terrific insulator against extreme heat. It doesn't burn. Go by a house that has just burned and the ductboard stands. Cockroaches, Keith Richards and ductboard will survive a nuclear attack.
    I like DIY'ers. They pay better to fix.

  12. #12
    Join Date
    Dec 2003
    Posts
    709
    You may want to explore the option of changing the furnace to a condensing furnace that will vent with 2 or 3" pvc and will have a sealed combustion chamber which draws 100% combustion air from outside. With your situation now you are going to sink some money into a furnace that may not be worth it.

  13. #13
    Thanx so much for all your responses!

    Yeah, my gut did feel that the HVAC guy was right, but I've never done anything like this before, so just wanted to make sure I was trusting the right person. I'm SO blown away that the contractor hasn't come across this in 29 years. He looked at it today and assured us the pipe would never become hot enough to be a fire hazard. We have to figure out how to proceed now, but I think we're going to put him on the hook for some, if not all, of the cost to fix it.

    The ceiling firestop is a metal plate that has been spackled to match the ceiling (done before we moved in) and the furnace guy seemed to think it was all right "as is".

    hearthman - what did you mean when you said the "horizontal run is not properly supported"? The dust got in because none of the ducts or furnace were covered during the construction, so we do plan to have all the ducts cleaned, too.

    Someone in the DIY.com forum mentioned that only high temp paint should be used on the single vent pipe. I guess our contractor didn't know that, either. Argh!

    The furnace is only 2 months old, so we don't want to change it right away. The door of the furnace opens into the middle of the room (facing the HWT). I'll have to find a manual online (it was installed by the previous owner as we were buying the house and they didn't leave it behind) to find out about the BTU rating, so we can check the size of the room. Although, the furnace guy didn't mention that, so it might be OK, but I'll definitely check it out with him.

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