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Flue Pipe Wrap?

JackFre Member Posts: 225
I'd contact your local comm/ind insulation distributor. In NE, Homans Assoc would be the call. ANY vent connector should be accessible for inspection. I have always preferred a reversed wye fitting with the branch capped on the bottom of any chimney liner where it enters the vertical chimney. That way you can pull the inspection cap and take a gander into the base of the liner. It sounds like you have a fairly short run so you could make access for inspection. I just got one of the Testo 300's (?) with the flexible tip. It is terrific seeing around corners.


  • Constantin
    Constantin Member Posts: 3,796
    Wondering if...

    ... any of you have ever resorted to wrapping boiler flue pipes with some sort of insulation. As you probably know, my Vitola is producing very low flue gas temperatures and I wonder if I can keep the flue warmer and reduce the potential for flue gas condensation by wrapping the section in the boiler room with some sort of approved insulation material.

    The flue is standard-issue 6" round flue duct. Any recommendations re: potential suppliers for the stuff?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    How about strips of mineral wool with a Tyvek "jacket"?
  • Alan R. Mercurio_3
    Alan R. Mercurio_3 Member Posts: 1,620

    Constantin, I can’t remember the name of the stuff off hand but if you call Sid Harvey’s or R.E.Michels they should be able to help you out. I had to use it in the past on job in a public building to bring it into compliance.

    Your friend in the industry,
    Alan R. Mercurio

    Your friend in the industry,

    Alan R. Mercurio

  • not tyvek as it is not repectful to heat

    I have had customers use "chicken wire" or stucco lath wire mesh with good success.
  • kevin coppinger_4
    kevin coppinger_4 Member Posts: 2,124
    Was it Roxul?

    I have seen it in fire/smoke proofing.1100F fireproof rating...kpc

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Definitely not respectful to flame, but it is ASTM 759 tested to 175-200 degrees F. I suppose something crazy could happen when it's containing a few inches of insulation surrounding a none-too-hot [normally] flue though...

    Dupont Nomex (flame-resistant suits are made from it) would almost certainly work.
  • Bob Harper
    Bob Harper Member Posts: 1,029
    case of the missing codes

    The gas and oil codes don't want you wrapping connector pipes. You cannot inspect them until they collapse onto the floor. If you want to get more heat into the chimney, locate the appliance a reasonable distance from the stack and line the chimney. If you are venting a condensing unit into an atmospherically vented chimney, you're asking for trouble.

    While we're on it, use at least 3 screws equidistantly spaced and place the seams up so they don't collect condensate.
  • Constantin
    Constantin Member Posts: 3,796
    Good advice...

    ... whatever material I end up having applied to the flue, I would want it to be easily removable and reinstallable for the very good reasons you stated. The current install is as optimized as it's going to get, distance-wise.

    The chimney flue is lined with smooth-wall stainless FasNSeal, insulated with perlite, and surrounded by masonary. The only area where the flue pipe is currently not covered with some sort of insulation or jacket is the boiler room.

    The boiler is a Vitola, and it takes the flue gases 10 minutes to get the temperatures up to 250°F, while the internal tank temperature raised from 114 to 147°F. I may need to ask my contractor to drill out one of the holes in the stainless bucket/target to raise the flue gas temperatures.

    However, before I do that, I thought that asking my heating contractor to retrofit a thin layer of insulation may reduce the heat loss from the flue pipe to the point where condensation does not occur. Furthermore, as we make our switch to B5, I imagine that the acidity of the flue gases will drop markedly and that any condensation at that point will be much more benign than it currently is.

    So many thanks to everyone that has contributed an answer, I appreciate the help. In the meantime, I'll pass the leads on to the contractor who will do the installation.
  • Glen
    Glen Member Posts: 855
    Koawool -

    might have a blanket material you could use. But as you have a Vitola - OB to boot, the recommended fix is to drill out one or more holes in the combustion chamber to raise your stack temp to suitable limits. Check your codes though - your jurisdiction may have addressed this already. BTW - if you do drill - please post before and after combustion analysis's. I have drilled out quite a few - it always amazes me how accurate the predicted temp rise vs the effeciency losses are, as stated in the Viessmann literature.
  • Dirk Wright
    Dirk Wright Member Posts: 142
    header wrap tape

    You can use an automotive product called header tape or header wrap. It's a fibrous tape that you secure to the pipe with metal clamps or mechanical wire. It's good to very high temperatures. You can unwind it easily, since it does not stick.
  • high temp insulation

    Constantine, Knauf is good to 1000F and if you wrap it mechanically and without adhesive you can indeed remove and reinstall.
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Boiler Operation

    Constantin, when I see flue temperatures running that low I question the mechanical operation of the equipment. Have you done a combustion test on this boiler-Oxygen and CO. Non-condensing equipment should operate over 275 degrees very quickly and should reach 300 degrees after 10 minutes. Even a high efficiency water heater that is heating water starting at 50 degrees attains flue temperatures higher than 250 degrees. The fact that it takes that long to go from 114 degrees to 147 degrees shows a poor rate of heat transfer.
  • Constantin
    Constantin Member Posts: 3,796

    Mr. Davis,
    It's great to see you here and I'm honored that you're helping me out. You're absolutely right, something does not add up. I am going to have to go back and re-run this test under more controlled conditions.

    It is entirely possible that a zone was calling for heat and hence depressing the boiler temperature. Other explanations could include a clogged nozzle, timing error, perhaps even a temp probe that is covered in soot. The enclosed back-of-the-envelope calculations (if done correctly) seem to show that the temperatures inside the boiler should have gone up about twice as much as they did.

    Yet, if the HX was bad, wouldn't the flue gases run a lot hotter than they did? Otherwise, where does the energy go?
  • Alex Giacomuzzi
    Alex Giacomuzzi Member Posts: 81
    Another Straight Forward Option


    While I was doing my installation, these same concerns about loosing temperature in the venting between the boiler and the chimney were running through my mind. I was concerned about that extra heat loss into the basement space. Not that I would not benefit from the heat, just that condensation was a potential concern.

    After reading the boiler installation manual closely for and talking with a very knowledgable installing contractor from Wisconsin who had installed the same boiler that you have a Vitola, I decided to put in Type B double wall vent pipe from the boiler to the chimney. It has really worked great.

    The air space between and the outer metal reflective skin does a nice job of keeping the heat where it should be in this application --- inside the flue.

    By the way... this contactor in Wisconsin ended up going back on the Vitola install and changing out the single wall to a double wall. If I recall correctly--(I am trying hard to recall), it was due to condensing in or leaking from the initial pipe. You may not need any insulation at all.........with a double wall. Good Luck.

    Regards Alex
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Where does the heat go?

    It never really gets produced. We have to deal with radiant heat which normally provides the highest percentage of heat that is transferred because the flame is quite a bit hotter than the flue gases that scrub the balance of the heat exchanger. Flame temperatures on gas can reach 3600 degrees at stoichimetric combustion which we can never attain. Oil can be a 1000 degress hotter. The amount of Oxygen in our flue gasses determine how hot the flame is and usually how big. Oxygen also represents the velocity the heat travels through the heat exchanger. When someone closes the air shutter on an oil burner the flame gets much hotter, yet the flue temperature goes down because of velocity. Nitrogen is 80% of the air we use. Excess air means 4 times more excess nitrogen which supercools the flame and steals the heat we need to transfer. I try to explain in class that if Oxygen was 0%, a gas flame is 3600 degrees and we are producing the maximum BTU's the fuel is rated. But when Oxygen is 6% the flame temperature is only 2800 degrees and the BTU value of the fuel that is actually available for transfer is considerably less. Unfortunately low flame temperatures create low flue temperatures which cause calculated efficiencies to be fabricated much higher than they really are. Because equipment efficiencies are based on calculations rather than real measurements most are often mislead. Any time I see flue temperatures below 275 degrees, even with 100 degree water in a boiler I find the equipment underfired and usually running with high Oxygen.
  • Constantin
    Constantin Member Posts: 3,796
    Thank you, Jim.

    Very, Very Much!

    Looks like I will buy a combustion analyzer after all. I will test my unit and report back the results. Cheers.
  • Mitch_4
    Mitch_4 Member Posts: 955
    are you

    using "C" vent? If so replace it with "B" vent, or other inherantly insulated vent connector.

  • Constantin
    Constantin Member Posts: 3,796

    Last night while rummaging about the boiler room, I looked up, then had the same thought as well. We transition from single-wall to double wall flue pipe just before the flue transitions to a different room before it hits the chimney. Your idea to go double-wall all the way back the boiler may be the least difficult option for my installer to accomplish.

    I also heard back from my GC that we still have leftover flue wrap from our chimney project for the 6" FasNSeal pipes that are inside. This could be another option.
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