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Thread: Chimney Cap question

  1. #1
    Join Date
    Mar 2016
    Location
    North Gower, Ontario Canada
    Posts
    244

    Default Chimney Cap question

    Hi all.

    This year I made a few changes to the evaporator. I have a 7 inch stack vs 6 inch from last year (actually used woodstove chimney pipe I got for a steal) and then also got a chimney cap to keep rain out. This is the typical chimney cap for woodstove applications (has about 3 inch gap then the top/cover part). Same length as last year (8 feet long chimeny, on a 4 foot evap)

    Noticed this year that when I put the AUF on, I'm getting fire coming out the gaps in the front door to the evap (now this is a homebuilt file cabinet arch..it's not airtight by any stretch) but it didn't do this last year. If I seal it up it pushes smoke out between the pans (they actually start to move off a bit so I know the pressure is being moved to there) and then eventually pushes through the door again.

    So I'm getting ready to take off the chimney cap as that is really the only change from last year..figuring it is constricting the flow too much, but wanted to pose this question before I do:

    Would lengthening the chimney, thereby increasing draft, counteract the restriction that the cap is providing? I have a few extra 3 foot pieces, so if I add an extra 3 feet, or even 6 feet, would the extra pressure be enough to push past the cap properly? It's easier for me to add a piece than to get on the roof to take the cap off, but I also like the cap to keep rain out so if I I take it off I need another solution.

    Just wanted to see if anyone has tried this before I proceed with one of the options..

    Thanks!.
    Paul.
    ______________________________
    2023 -30 trees -24 vacuum, 6 buckets. ~1,845 L sap; Syrup count: 49.25L
    2022 -30 trees -24 vacuum, 6 buckets. ~1,530 L sap; Syrup count: 48.65L
    2021 -29 trees -23 vacuum, 6 buckets. ~1240 L sap; 34.5L of syrup
    2020 -30 trees 32 taps. ~900 L sap; 27.1L Syrup.
    2019 -27 trees 31 taps. ~725 L sap; 22.2L Syrup.
    2018 -19 Trees 20 taps. ~750 L sap; 18 L Syrup
    2017 -4 trees 4 taps. ~60 L sap; 1.5 L Syrup

  2. #2
    Join Date
    Mar 2016
    Location
    Kawartha
    Posts
    65

    Default

    I used a cap the first yr worked fine for a few boils and started smoking when I went to check it out found that the screen around it was starting to plug took the screen off and has worked great
    Sapman

  3. #3
    Join Date
    Mar 2017
    Location
    Oakville, ON
    Posts
    144

    Default

    What is clearance from top of chimney to underside of cap? If it's less than radius of chimney then the cap itself will cause pressure increase. For 7" chimney need at least 3.5" gap, preferably a little more because of change of direction. Also if there is screening on it, take the screening off. Not needed in sugar house application and screening can greatly reduce flow.
    2023 - 130 taps, 90L from 4,000L as of mid March
    2021 - 84 taps, 50L from 2100L
    2020 - 100 taps on buckets, 21L syrup from 2700L so far (FEB 26-Mar 13) and then the pandemic hit! End of our season!
    2019 - 62 taps on buckets, 95L syrop from 3215L sap
    2018 - 62 taps, collecting by hand, 90L syrop from 3200L sap
    2017 - Lapierre Waterloo Small mini pro with 40 taps
    2014 - 2016 40 taps making one or two batches on a 2x6 flat pan over an open arch as it would have been done in 1900

  4. #4
    Join Date
    Mar 2016
    Location
    North Gower, Ontario Canada
    Posts
    244

    Default

    Ok, so I've taken down the chimney cap. The clearance from the top to the underside of the cap is about 5 inches, so that should be good. I've also removed the screening from it as well. I'm also thinking I should remove the horizontal support that was behind the screening, and just leave each vertical support that holds the cap on (the red circled area in the pic). Does that make sense?

    Thanks for the advice!
    Chimney Cap Picture.jpg
    ______________________________
    2023 -30 trees -24 vacuum, 6 buckets. ~1,845 L sap; Syrup count: 49.25L
    2022 -30 trees -24 vacuum, 6 buckets. ~1,530 L sap; Syrup count: 48.65L
    2021 -29 trees -23 vacuum, 6 buckets. ~1240 L sap; 34.5L of syrup
    2020 -30 trees 32 taps. ~900 L sap; 27.1L Syrup.
    2019 -27 trees 31 taps. ~725 L sap; 22.2L Syrup.
    2018 -19 Trees 20 taps. ~750 L sap; 18 L Syrup
    2017 -4 trees 4 taps. ~60 L sap; 1.5 L Syrup

  5. #5
    Join Date
    Jan 2006
    Location
    Oneida NY
    Posts
    11,547

    Default

    On an evaporator it is very uncommon to have a cap when boiling. Some use a flip open cap so it can be closed when not boiling.
    If you still get smoke, you may just need more height. Yes, 2x the evaporator length is the guideline, but several things can affect what you need. The surrounding hills, buildings, trees and other things often make more height necessary. The space near the back of your evaporator (inside the arch) can also affect it. I suggest you just add 2' more, using single wall pipe on top of what you have, if that doesn't correct it, add 2' more.
    Also, you say smoke, if you get smoke out once you have a good fire going, your wood is either wet, not split small enough or punky or for some other reason it is not burning hot enough. On my evaporator after the initial lighting you can not see any smoke, it is clear once the fire gets going hard. Once going hard, even punky wood, if dry will not smoke.
    Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
    Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
    Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
    After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.

  6. #6
    Join Date
    Mar 2016
    Location
    Kawartha
    Posts
    65

    Default

    Hey Paul all I did was remove the screen and it has worked great ever since. I see the part you are talking about I would try it like that first .
    Sapman

  7. #7
    Join Date
    Jan 2008
    Location
    Frankford, Ontario
    Posts
    1,045

    Default

    Increasing stack length increases draft fora natural draft arch.
    As soon as you add a blower, increasing stack height has NO real effect on the draft. (If anything it increases restriction - but it's negligible)
    Big_Eddy
    Eastern Ontario (Quinte)
    20+ years on a 2x3 block arch,
    Homemade 20"x64" drop flue since 2011

    Build a Block Arch
    Build a Flat Pan
    Build a Flue Pan
    Sweetening the Pans
    Build a Bending Brake
    Using a Hydrotherm
    How much Sap to Sweeten?

  8. #8
    Join Date
    Mar 2011
    Location
    Potter County, PA
    Posts
    815

    Default

    With forced draft, stack height is no a factor in the burn. If you are getting smoke and flames out of the cracks and under the pans, you have created a pressurized arch.
    Remove the stack cap. Remove any dampers that are in the pipe.
    2008 4 buckets
    ~
    2016 1300 vac tubing
    18x24 sugar shack
    2x6 Grimm Lightning w/preheater on natural gas
    7" full bank press
    CDL 600 RO
    2000 Sonoma w/ 200gal tank
    2003 Duramax w/ 500 gal tank
    2 sap guzzling kids
    very patient wife!

    Same ol' addiction

  9. #9
    Join Date
    Mar 2016
    Location
    North Gower, Ontario Canada
    Posts
    244

    Default

    Thanks for all the advice everyone!

    I don't have a damper so that's not an issue. I've removed the stack cap to take the screen off.. I may just cut the connections and add a hinge to convert it to a flip-open cap.. Or I'll just leave it off and put it back on as needed (i.e. when it rains and during the off season)..

    The way the weather is going here I may only 1 or 2 more boils left anyways.. :-(

    Happy sugaring!
    Paul.
    ______________________________
    2023 -30 trees -24 vacuum, 6 buckets. ~1,845 L sap; Syrup count: 49.25L
    2022 -30 trees -24 vacuum, 6 buckets. ~1,530 L sap; Syrup count: 48.65L
    2021 -29 trees -23 vacuum, 6 buckets. ~1240 L sap; 34.5L of syrup
    2020 -30 trees 32 taps. ~900 L sap; 27.1L Syrup.
    2019 -27 trees 31 taps. ~725 L sap; 22.2L Syrup.
    2018 -19 Trees 20 taps. ~750 L sap; 18 L Syrup
    2017 -4 trees 4 taps. ~60 L sap; 1.5 L Syrup

  10. #10
    Join Date
    Mar 2016
    Location
    North Gower, Ontario Canada
    Posts
    244

    Default

    Just following up for everyone. I put the chimney cap back on with the only modification being the removal of the bug screen. That's all it took for the evaporator to no longer be pressurized. The bug screen was providing too much restriction. I was happily boiling in the pouring rain today (well.. as happy as one can be in that kind of damp weather!).

    Thanks again for all the advices provided!
    Cheers!
    Paul
    ______________________________
    2023 -30 trees -24 vacuum, 6 buckets. ~1,845 L sap; Syrup count: 49.25L
    2022 -30 trees -24 vacuum, 6 buckets. ~1,530 L sap; Syrup count: 48.65L
    2021 -29 trees -23 vacuum, 6 buckets. ~1240 L sap; 34.5L of syrup
    2020 -30 trees 32 taps. ~900 L sap; 27.1L Syrup.
    2019 -27 trees 31 taps. ~725 L sap; 22.2L Syrup.
    2018 -19 Trees 20 taps. ~750 L sap; 18 L Syrup
    2017 -4 trees 4 taps. ~60 L sap; 1.5 L Syrup

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