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Exterior Chimney

Jlamb
Jlamb Member Posts: 14
in Gas Heating
Does anyone know the correct definition of an "exterior' chimney?

And when you line an exterior chimney with a stainless steel liner, is that not considered insulated?

Comments

  • unclejohn
    unclejohn Member Posts: 1,833
    edited March 2015
    One wall of chimney exposed to outdoors. It's not insulated it's lined.
  • vaporvac
    vaporvac Member Posts: 1,520
    The SS liners can have insulation, but it's not always the case. s
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
    icesailor
  • Jack
    Jack Member Posts: 1,048
    It is common for an outside lined chimney to condense. This can be exacerbated by oversized equipment. Exterior chimneys are just tough to use...confidently.
  • Tim McElwain
    Tim McElwain Member Posts: 4,642
    If you look in the codes NFPA 54 and International Fuel Gas Code you will find that exterior chimneys are not allowed for gas equipment.
    icesailorZman
  • Jlamb
    Jlamb Member Posts: 14
    Hmmm so technically speaking all chimneys with the rear exposed are not suitable for gas equipment?

    There are a lot of gas conversions in Maine taking place and I can see this being a problem.

    Especially because more than half of all chimneys have one side exposed.
  • Jack
    Jack Member Posts: 1,048
    Jlamb said:

    Hmmm so technically speaking all chimneys with the rear exposed are not suitable for gas equipment?



    There are a lot of gas conversions in Maine taking place and I can see this being a problem.



    Especially because more than half of all chimneys have one side exposed.

    Actually, the problem is that masonry chimneys have absolutely no place in venting todays equipment, oil or gas. masonry chimneys are typically oversized heat sink. They are like the adobe homes in the southwest. Absorb heat all day and give it up to the interior at night...except that they never give it up to a positive outcome. They just suck the heat and energy out of the flue gases and systems suffer.
    The gas industry, which as public utilities was highly regulated, went through this in '92 when the energy codes required a minimum of 78%. The old draft hood equipped furnaces were in the low 60% range. This was a profound difference and took subsequent issues of '54 to get tighter and tighter in recognition of the physics of combustion and dew point problems. The oil industry which isn't regulated in the same way has been able to "avoid", intentionally, relining issues, although the physics of combustion are the same. For reference check out Appendix E in 31.
    Net/net, the real issue is that we are venting 21st century appliances with 11th century technology when we use any masonry chimney. In todays world with todays equipment masonry chimneys are excellent architectural devices, but terrible mechanical devices!
    SWEIJlamb
  • Tim McElwain
    Tim McElwain Member Posts: 4,642
    The solution if possible is to run "B" vent up through the existing chimney using the chimney as a chase. The code allows this and the Handbook for NFPA 54 shows a picture of this being done.
  • Jlamb
    Jlamb Member Posts: 14
    Great! Thanks for the help!
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728
    Tim, correct me if I'm wrong but if you use a liner, and install it in a existing tile lined chimney is then falls under the B vent sizing charts.
    No?
  • Tim McElwain
    Tim McElwain Member Posts: 4,642
    Most liners are actually 20% less capacity than "B" Vent. I suggest using the charts from the manufacturer of the liner.

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