furnace vent

Discussion in 'Shop Talk' started by bill not in oh, Oct 23, 2006.

  1. bill not in oh

    bill not in oh Well-Known Member

    Messages:
    1,869
    Joined:
    Jul 27, 2004
    Location:
    Earth
    My furnace and water heater vent through the roof via a masonry chimney. The cover seems to have blown off the top, so I now get small amounts of water down through the vent. Question is: Since it's not a fireplace chimney, do I need an actual chimney cap, or is a roof vent useable for this application? The chimney is 18" X 18" and I'm having a hard time finding one that size and even the smaller ones I've found are pretty pricey. I'm just not sure if there are airflow issues that could be created by using a vent. The last thing I need is a bunch of carbon monoxide in the house.
     
  2. Ross

    Ross Moderator Staff Member Supporter

    Messages:
    13,086
    Joined:
    May 9, 2002
    Location:
    Ontario
    We're talking oil fired or gas fired? 18x18 is the outside dimensions right? What size is the flue? 8x8? That's a 6" round equiv. It's too big for gas fired appliances to use most run on 4" and you want B vent or A vent sized to suit the gas or a gas liner (aluminum) down the masonary chimney. A masonary chimney must have a good liner and cap, the "cap" for oil fired is the cement top that supports the liner (clay) not the ash screen you see on wood fire place or wood stove caps. You see lots of ash screen caps on oil fired vents too and while not proper (here) they only rarely cause problems. So if your stuff is gas you may need a liner and it will have a gas vent cap if it's oil you need to fix any of the cement or brick and ensure the liner is sound (no flakes or cracks in the clay liner or clean out) but it doesn't need a metal cap. Unless its metal lined (for oil its stainless steel) already then it needs that metal cap too. That's a bit confusing and Ohio isn't Ontario and the code will be somewhat different.
     

  3. bill not in oh

    bill not in oh Well-Known Member

    Messages:
    1,869
    Joined:
    Jul 27, 2004
    Location:
    Earth
    Thanks Ross. Sorry I wasn't more clear about this. Both the furnace and water heater are gas fired and use 4" vents that join together in the basement at which point a 6" vent pipe goes up through the house/attic to where it exits through the chimney which is simply 'decorative'. The chimney is essentially a 16X16 (inside dimension) hole in my roof that I need to cover from the elements. The vent pipe has no cap as there was (at one time) a cap on the chimney itself, so rain/snow was not an issue. It has now blown off (mounting brackets rusted through) and water will enter the pipe and attic space when it precipitates. I want to cover the opening to prevent this without restricting the exhaust flow from the two appliances.
     
  4. mdharris68

    mdharris68 Well-Known Member

    Messages:
    502
    Joined:
    Sep 28, 2006
    Location:
    NE Kansas
    Does The Flue Pipe Extend Above The Fake Chimney? If So, Have A Sheetmetal Shop Bend You Another Cap And Cut Out Hole For The Flue Pipe And Get Another Cap For The Vent Itself. You Need To Make Sure That Your Flue Gasses Are Exiting Properly. Don't Take A Chance On This One, As It Could Be Your Last. Get Professional Help If Your Still Not Sure.
     
  5. bill not in oh

    bill not in oh Well-Known Member

    Messages:
    1,869
    Joined:
    Jul 27, 2004
    Location:
    Earth
    I wish... That would simplify the situation somewhat. I think I'll see if I can add an extension to bring it above the top of the chimney and
    I do know someone that has a sheet metal brake that could probably do this.