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Condensing boiler air/vent via chimney

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Bill Clark
Bill Clark Member Posts: 12
in THE MAIN WALL
eluded me. I found several 29-4 flex liners which were specifically not approved for use with condensing boilers and several approved rigid 29-4 liners.

Bob, do you know of an approved flex liner? That asked, I'm aware that no metallic vent is described in the Knight IOM and that the boiler's approval might be contingent on PVC.

Thanks to all...interesting :)

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  • Bill Clark
    Bill Clark Member Posts: 12
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    I would like to replace an old wall-hung with a Lochinvar Knight 80. Like any condensing boiler, the Knight's IOM specifies all the means which may be used to vent the boiler. Conspicuously missing is the idea of running PVC/CPVC vent and air piping up an existing chimney from the boiler all the way to the chimney top and beyond (according to the IOM).

    Can a chimney be used as a conduit for the two 3" pipe runs? Or is this a prohibited flue-lining scheme? The chimney, currently lined with 8x12s, can be capped atop and left open at the bottom so some heating of the PVC near the chimneytop will naturally occur; ie, until the PVC extends a foot or so beyond the cap, the PVC runs will be essentially 'inside'.
  • Gene_2
    Gene_2 Member Posts: 59
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    Bill

    > I would like to replace an old wall-hung with a

    > Lochinvar Knight 80. Like any condensing boiler,

    > the Knight's IOM specifies all the means which

    > may be used to vent the boiler. Conspicuously

    > missing is the idea of running PVC/CPVC vent and

    > air piping up an existing chimney from the boiler

    > all the way to the chimney top and beyond

    > (according to the IOM).

    >

    > Can a chimney be used

    > as a conduit for the two 3" pipe runs? Or is this

    > a prohibited flue-lining scheme? The chimney,

    > currently lined with 8x12s, can be capped atop

    > and left open at the bottom so some heating of

    > the PVC near the chimneytop will naturally occur;

    > ie, until the PVC extends a foot or so beyond the

    > cap, the PVC runs will be essentially 'inside'.


  • Gene_2
    Gene_2 Member Posts: 59
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    Bill

    We have done that many times. A few things to watch are:

    Is the chimney an exterior one? You may need to insulate the exhaust.

    How tall is the chimney? You can run past the venting lengths indicated by the manufacturer but the boiler starts to be derated btu wise.

    Is the chimney a straight shot? Nothing worse than finding out the mason had to 45' somewhere in the flue passages.

    Hope this helps, Darin
  • Bill Clark
    Bill Clark Member Posts: 12
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    Straight shot up the chimney?

    I wish! The chinmey has a 10* easy and a 20* hard bend. But I'm motivated enuf to disassemble the fieldstone chimney to expose the hard bend for the inspector. I hear you re vent insulation; maybe the last 2'.

    My only other option is to pop out of a flat roof having 3' typ snow load right in front of evacuated-tube collectors. Logic indicates that would require a ~2' 'heated' structure, NTM trips to the roof to clear collectors. This option has other issues.

    Thanks Darin! Good ratification for the inspector.
  • Bob Harper
    Bob Harper Member Posts: 1,035
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    stainless flex liner?

    Why not just drop a 3" stainless AL29-4C liner down the chimney and be done with it? It will easily negotiate those offsets and you can get one listed to UL1738 for Cat.IV condensing furnaces and boilers. 30 minute job.
  • Paul Rohrs_5
    Paul Rohrs_5 Member Posts: 134
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    Commercial Job

    We vented to Knight's out the existing chimney on a commercial job. It turned out very well. We had an existing 8" flue going to a chimney with a liner. The liner was in pretty good shape.

    Here are some of the pics. Matt J was a true craftsman of venting. Those are 4" PVC lines. Matt also bent the metal cap and chem-caulked it down on the chimney cap.

    regards,

    PR

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  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
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    Paul

    I have got a very similiar install starting in a few weeks. Just what was used to make the flashings, etc, at the top of the chimney? I've been concerned about getting a water tight cap for the chimney we are using as a chase. Ours is a 21 inch cement asbestos chimeny and we have one 6 inch b vent also poking through.
    Thanks.

    Boilerpro

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  • Paul Rohrs_5
    Paul Rohrs_5 Member Posts: 134
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    Vent

    Matt bent up the metal on the break, chem-caulked it down to the old concrete chimney cap, and we also used storm collars around each 4" line. We used some 5" single wall to sleeve one inlet and outlet to extend it enough for each storm collar. Otherwise, they would have butted up against each other. The intakes have the u-bend facing South,the exhausts each face North, so...the West side is the intake and exhaust for one boiler, and the East side which was extended, also serves one boiler. Picture 5034 is a good reference.

    Edit: Had North Exhausts and South Intakes turned around- now it is revised.
    Paul

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  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
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    It also..

    Looks like you used some 5 inch start collars at the flat and used really short pieces of 5 inch pipe to raise the lower storm collars up some. I think I may bump my strom collars up some to allow for snow accumulation. I am forwarding the pic to the sheetmetal ship that is making the cap for the chimney.
    Thanks again!

    Boilerpro

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  • Ike Gatlin
    Ike Gatlin Member Posts: 65
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    damn manufacturers....

    Bill,
    Yes the I&O does not specifically cover this type of installation. It is entirely possible to do this. Paul has shown a perfectly acceptable method, I am attaching photos of an installation in Montana that is configured in such a fashion.

    Ike Gatlin
    Lochinvar
    PS. Thanks for using the Knight.
    These 3-210kbtu replaced 1-1.0mbtu cast iron. It was -5 degrees and 1-210 ran at 20% input all night long and met load.
  • Dan_15
    Dan_15 Member Posts: 388
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    How did you install the PVC pipe?

    OK,
    I like the idea of using a chimney as a chase but how did you get the PVC pipe in place? I assume if joined before installation, you had a 20-30foot pipe blowing in the breeze?
    If you installed and glued each section to the last one inserted as you put it in...any problems?
  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
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    Upside down sensors

    Did you know that those outdoor sensors in the last pic are upside down. Did that on an early tekmar job and soon found out that they can collect water that way. Conduit connection needs to be down or maybe sideways, but never up.

    Just FYI

    Boilerpro

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  • Paul Rohrs_4
    Paul Rohrs_4 Member Posts: 466
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    Curious

    Ike,

    By the look of the picture titles, they used the internal sequencer and the cascade functions. Couldn't they have used only one sensor?

    Regards,

    PR

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  • Paul Rohrs_4
    Paul Rohrs_4 Member Posts: 466
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    \" I'll take Manual-Reset High-Limits for $400.00 Alex\"

    Ike,

    Don't they believe in MRHL's, flow-switches, or LWCO's in Montana?


    Regards,

    PR

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  • Ike Gatlin
    Ike Gatlin Member Posts: 65
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    why yes...

    They had used individual sensors prior to our arrival and initiating the cascading. It doesn’t make the controls any difference if it is done with multiples or one sensor. The only one it "reads" is the one attached to the lead boiler.



    Ike
  • Fred Campbell
    Fred Campbell Member Posts: 80
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    Pulling PVC thru chimney offsets

    Some one posted here a while ago about "heat blanket" bending the PVC to pull it through an offset in the liner or chimney. Apparently, get it hot enough in the predetermined spot and pul like hell. I was impressed at the ingenuity. Beats the heck out of knocking out bricks and trying to glue offsets. Nothing like a nice straight flue to work with.

    BP, if your tinner is good enough he can "flange" your C-C openings for your pipe OD. That is, cut the opening a bit smaller and roll the edges up. I've done it on site with linesman's pliers. Work the metal to a tight fit to your PVC and caulk the joint. I use silicone. Make sure the cap is cross broke to pitch to the edges. If it's huge you may have to add some center support to stp sagging. Do the same with your B-vent penetration. I know of no storm collar for PVC but a standard 6" B-vent collar above the aforementioned fit and your good to go. I silicone all of my storm collars..even B-vent has a seam.

    TG
  • Paul Rohrs_4
    Paul Rohrs_4 Member Posts: 466
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    Dan

    Yes, we glued 10' sections together one-at-a-time, and lowered them down. We also had a riser clamp to hold the weight that we support it while gluing the joint.

    We were 20-25 feet up on the roof and I would not advise doing it on a windy day. Matt applied cement,stood the pipe on end, mated the joint, then lowered it down after the cement set up. It actually went pretty fast.

    Regards,

    PR

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  • Guy_6
    Guy_6 Member Posts: 450
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    Watch

    Be careful when venting an appliance in any material other than what is called out in the manual. An inspector can shoot it down, or worse, the material may not be appropriate for long term use. If it were to break down within the chimney the damage would be hidden until it was too late and well advanced. Not to mention the fact that a tech would hard pressed to consider such a failure.
    There is a hunt on for flexible PVC that will conform to usable standards in situations like this.
    BTW- Beautiful venting pictures! A valuable tool for educating.
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