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flue condensation

clammy Member Posts: 3,091
wondering everybody seems to use electric ingitions over standing pilots.have they like myself seen flue damage from condesation. this is on clay lined systems and chimmey on the outside walls on these jobs i go with standing pilots or line the chimmey i rarely see any thing in equip. instruction sheets giving info. on and most suppliers look at me if i where insane when i bring the nsubject up. what does everybody leave it to a chimmey guy.i seem to be the only one who notices it.am i insane
R.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating


  • Dana
    Dana Member Posts: 126

    I think you'll find that most of the better mechanics/contractors deal with this situation as you do. As in any buisness, there are those that do know what they are doing and those that don't. Being in Massachusettes, our inspectors are all over this as well as make-up air. Can't speak for the rest of the country.
  • Boilerpro_2
    Boilerpro_2 Member Posts: 89
    Frim believer in standing pilots

    for this and other reasons.

  • rob
    rob Member Posts: 64
    It helps to read

    the installation and operation manual. Most furnaces/boilers are either Category I or 1V. Category I systems must be vented per NFPA Vent Code. Most (all) masonary chimneys need to be lined with B-Vent or an insulated liner and the vent connector will need to be sized per the tables, double wall B-1 is always preferred.
    Flue condensation can also be attribued to lack of ample combustion air. This is also addressed in the I/O manual.
    If we expect it to work right, it's gotta be installed right.
  • Most manuals and NFPA

    give pretty straight forward rules on chimneys and liners. A lot of equipment is not allowed to be installed into unlined or lined chimneys. Outside chimneys are always a problem as to cooling and getting below dew point in some area of the chimney.

    Everyone who installs or services equipment should be required to attend a minimum of one week training on combustion and venting as it relates to installtion (and even that is too short but who would go longer). That also includes inspectors. It takes a lot of knowledge to overcome many of these problems that are constantly coming up on this site. We can only give sometimes very short answers here. You need to sit down and get the entire story. There are no short cuts. I have spent days after days trying to adjust equipment and systems to get them to operate correctly especially when it comes to air and venting problems and working on reaching acceptable levels of combustion analysis with low or no CO. The way they build some of these building it is no wonder we have problems.
  • What you are seeing

    is the downside of higher efficiencies. You're right. Standing pilots, along w/ the gas water heater, kept the flue tiles warm, dry, and cozy. Helped the heat exchangers last 30 years too. But, the pilots burned $10 of gas a year. We just had to do something about that.

    So we went to spark ignition, or worse yet, hot surface ignitors. We added vent dampers and tightened up the heat exchangers. Why, we even went to induced draft units with stack temperatures just above condensing, maybe. And. We stuck the vent pipe into your old, oversized, brick chimneys, w/ square tile linings. Not your fault. That's how chimneys were built. Still are.

    So now it's raining in your chimney. And. That ain't all water. Nope. That condensate could be mixed w/ olive oil for your salad dressing. Nicely acidic. Just the kind of thing your tiles need. So. What to do?

    Follow the advice of the other Wallies. Get a copy of the appropriate NFPA Codes. For oil, it is NFPA 31. NFPA 211, I believe, is the other. Learn the codes. Buttonhole your supplier of choice. Line up classes w/ the guys who supply his venting line. Then go make a bundle on venting the equipment properly. Don't look at it as a problem. It's an opportunity - for you.

  • Jim Davis
    Jim Davis Member Posts: 305

    If a pilot can keep a flue from condensing, the pilot is too big. Pilots usually create more destruction than they prevent. Condensation is caused by low flue temperatures(even 80% efficient equipment should be a minimum of 300 degrees), poor venting and negative pressures in the mechanical room.
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