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Chimney liner

RianS Member Posts: 104
Thanks Bob, I also checked the code book and 6.5.7 reads the liner should not be smaller than the appliance connector. So I don't know what to do other than installing then the way I always have. We installed one with a replacement boiler a few years ago and it's been a problem ever since. This boiler fires at .65, its a ranch home with a chimney height of 20 feet and 3 sides exposed to the exterior. The original chimney was 12"x12" clay liner. Every time it drops below 30 degrees the SS liner (6") sweats. I think if we could reduce it to 5" it wouldnt sweat. So instead of reducing it, we filled the chimney around the liner with vermiculite. I hope that solves the problem. This is the only one that ever gave us a problem but I can see it becoming an issue with future installs. We down size liners for gas equipment all the time if you do it by the chart. Why not oil?? Any other suggestions would be great. Thanks Happy Thanksgiving Rian


  • RianS
    RianS Member Posts: 104
    Chimney liner

    Does anyone know if there is a chart available for sizing stainless steel chimney liners for oil fired systems? I always use the one I have for sizing gas heat liners but don't have one for oil. Every time I install one I always went by the size of the connection on the unit. The supply house guys can't help me with this, all they stock is 6" and 7" kits. I have always thought there is a chart for correct sizing but have never found one. I e-mailed Z-Flex several times for this info but they never return my e-mails. Any help would be appreciated. Thanks Rian
  • Bob Harper
    Bob Harper Member Posts: 1,028
    NFPA 31

    appendix in the back. Sizing by the collar is a joke! You're going to use a 7" liner for 0.65 GPH when a 5" will do just fine? Ridiculous.

    These charts are very limited in range so you'll likely have to interpolate but that's really all there is for oil.
  • Ken D.
    Ken D. Member Posts: 836

    I do know that Metalbestos had a chart. If your supply house can't help you, the manfacturer should be able to. If they don't, try another manufacturer.
  • Joe Brix
    Joe Brix Member Posts: 626
    A .65 nozzle

    would probably be on a smaller higher efficeny boiler
    like a Buderus G115 which has a 5" breech to start. It probably would have been raining in the 12 x 12 with that little BTU's going up the stack.
  • Bob Harper
    Bob Harper Member Posts: 1,028
    oil appliance mfrs.

    These guys are a bunch of spoiled cry babies. While the gas industry makes diffrent sized appliances with matching vent collars and detailed venting guidlines, these bums leave everyone hanging. They make one size fits all with a 7" collar knowing it will probably end up in a small home at less than 1.0 GPH.

    Yes, NFPA 31 calls for the smoke pipe to be the same size as the appliance collar. This is to cover the butts of the appliance mfrs. However, it does not apply to liners. Why else would they post sizing tables showing liners less than 7"?

    It's all a bunch of BS. The oil industry needs to get its heads out of you know where on venting parameters.

    As for practical concerns, I'd just like to see the code required cleanout on an oil flue once in awhile.
  • RianS
    RianS Member Posts: 104

    Actually it's a Burnham PV713 boiler. It has a 6" connector on it. We would have never left it vent into the original 12x12 and even with the 6" SS it would sweat. I couldnt have said it better Bob.
  • airflo mech
    airflo mech Member Posts: 11

    z/flex.free sizing charts for stainless and alum.oil and gas liners.
  • Techman
    Techman Member Posts: 2,144

    Going by memory here, I thought the flue size was allowed to be down sized by 1",oil or gas! Do I have to go read my books again?
  • Dave Belisle
    Dave Belisle Member Posts: 68

    Even though NFPA 31 may state the vent connector size may not be reduced , they also defer to the manufactures specifications.

    As has been mentioned the last cast section with the vent connector may be on a three section boiler or a seven section, it is the same section. The manufactures will give specifications for the flue pipe size and the smaller boilers may be reduced per there specs.

    I have had inspectors question connector sizes and pipe clearances, but when I show them the manufacutres specs, they ask for a copy for there files and always go by that...

    I haven't had to change one yet........

    Dave in NH

  • RianS
    RianS Member Posts: 104
    Oil appl. mfg.

    Speaking of CYA, I did an inspection on a Bryant CI boiler the other day for a Realtor. The owners’ manual was actually there at the boiler. As I paged through the manual I saw they actually call for 18" of clearance to combustibles from the smoke pipe. This boiler was only 2 years old! With the stack temps. as low as they are anymore, why is it still necessary to have 18" to combustibles? Gas is only 6" and I know some 80% furnaces that have a higher stack temp. than an oil fired CI boiler.
  • Chimney connector pipe clearances on oil.


    The clearance is not intended for the normal operation of the boiler, it is for when things go wrong. However you can not plan and time your “accidents” so it applies to all.

    I have actually measured the stack temperatures of more than one boiler while they were dry firing, for training purposes.

    The stack temps on the boilers were around 375 to 420 gross when full of water, and went over 1000 degrees in less than an hour, when the boiler was devoid of water.

    While in the field I have also seen chimney connector pipes connected to oil "loaded" boilers, where the pipes were glowing while the oil was burning off. That is why the primary control manufacturers have tried to incorporate reset restriction on the control programs, to protect against the homeowner who hits the reset 50 times, then lies about it to the tech.

    The 18" clearance is to protest combustibles when the boiler is NOT operating properly. That is what confuses many service techs.

    They repeatedly remove and re-install a chimney connector pipe on boiler during a cleaning, where the chimney connector pipe was 6" away from the ceiling for the last 20 years without a problem.

    They can't understand why they are held accountable when the ceiling catches fire after the boiler malfunctioned.

    "But it was that way before" or "But we always do it that way", doesn’t matter after the fact.

    Ed Carey
  • JackFre
    JackFre Member Posts: 225
    NFPA 31 and venting tables

    What we do on the 31 committee is answer our mail. All actions, well most anyway, come as a result of mail we receive with an issue which someone in the business feels needs to be addressed. We need to hear from you on your concerns and positive suggestions.

    The App E sizing guidleines in 31 were originally developed by Rich Krajewski and John Strasser at Brookhaven in I think 1994. As an appenedix item they are not a part of the code. Chimney sweeps and others I have spoken with have found them to function very well...but they are not a part of the code. We will be starting a new segment of the 31 code discussion in the spring. Your cards and letters would be most appreciated.

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