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  1. Joful

    Joful Minister of Fire

    Joined:
    Mar 7, 2012
    Messages:
    6,386
    Loc:
    Philadelphia
    Had the Jotul 12 Firelight (large cat stove) whuffing again tonight. Started about 1 hour after a big reload, in a stove that had already been burning about 2 hours on a smaller load. This is the second time this has happened in my 8-month affair with this stove (read, "any stove"). Situation was same both times:

    Outside temp > 45'F
    Stove burning > 2 hours
    Full load of wood on reload
    Air control shut way down

    The first time it happened, several weeks ago, I thought it was because I had throttled down the air too quickly. So, I've been lowering it just a bit at a time whenever I throttle down since, taking 10 - 20 minutes to reach min setting. Of course, that did not prevent a re-occurrence tonight, so I started hunting for other possible causes.

    So, according to one thread I found here, this problem can happen any timE you have a full load of fuel and a too-low air supply. In other words, all the advice I've received from the local dealer on loading her full and then burning with the air control set to min fir a long burn is not always a safe way to go. I'd not be comfortable leaving this stove set up for a long burn, based on these two incidents. What am I missing?

    Stove has proper 6" black steel (approx 5 feet) into 8" round clay (approx 12 feet), which should not be too bad a setup.

    Thanks!

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  2. begreen

    begreen Mooderator Staff Member

    Joined:
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    Loc:
    South Puget Sound, WA
    It sounds like the air is being closed off too early. This may be due to lower draft or wood that is not as dry. Milder weather and the larger flue pipe will make the stove more sensitive to draft. If the wood is not really dry, then the air may need to remain open more than normal until the wood is fully charred. It also could be the wood species. If locust or oak the fire may need a bit more air in milder weather.
    Backwoods Savage likes this.
  3. Joful

    Joful Minister of Fire

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    Maybe! The wood was definitely not charred all over, or even lit all over, as I wanted to start cranking down on the air before the stove got too hot (was a warm evening). Just surprised me that it started an hour after the last reload, instead of sooner.

    I do think that stove is oversized for the space, as I'm only heating 1100 sq.ft. It probably would be fine for a more seasoned stover, but likely makes things more complicated than they need to be for this open fireplace burner.
  4. Bub381

    Bub381 Minister of Fire

    Joined:
    Feb 4, 2011
    Messages:
    865
    Loc:
    Mid-coast Maine
    I have a Rangeley in a little over 1300 sq ft and it's severly oversized.Can't even use my 2ndaries.Have to run it at 300 all the time.
  5. begreen

    begreen Mooderator Staff Member

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    Open some windows for now.
  6. ScotO

    ScotO Guest

    +1. That's what we do, esp. In the spring shoulder season. Lots of windows, if need be. I actually have to open the stove up to "3". I usually run it all winter either at "1" or shut down. Draft really gets lazy when the relative air temperature outside is close to the ambient temp inside. At least in my situation.
  7. MasterMech

    MasterMech Guest

    In my 1260sq ft, we run it for one good hot fire in the evening, leveling out at about 450-500 on the stovetop. House holds that heat all night and picks up enough solar during the day to stay over/around 70 degrees.
  8. ScotO

    ScotO Guest

    70 degrees......my wife cringes if I let it get that cold in the house. ;)
  9. Gark

    Gark Minister of Fire

    Joined:
    Jan 27, 2007
    Messages:
    808
    Loc:
    SW Michigan
    Joful- ditto on what begreen said about reduced draft in milder temperatures. Here, with our setup, temps below 20f. cause too much draft while temps in the 45f. range barely allow enough draft to pull air through the stove. Way I see it, inadequate draft means the flue can't pull the unburned gasses out of the firebox through the cat fast enough. So the gasses build up in the firebox and suddenly decide to ignite. Once we insulated the previously uninsulated liner, back-puffing has been eliminated. Before insulating, backpuffing was common. Draft strength reduces whuffing and outdoor temps affect draft.
  10. Joful

    Joful Minister of Fire

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    Mar 7, 2012
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    6,386
    Loc:
    Philadelphia
    Interesting, as I have a 6" black steel pipe feeding a relatively short 8" masonry chimney. Not the greatest setup for avoiding whuffing, from what I've read. I wonder if there's room for, or merit for, installing a 6" insulated liner in that 8" masonry chimney, so I have 6" bottom to top?
  11. Slow1

    Slow1 Minister of Fire

    Joined:
    Nov 26, 2008
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    2,663
    Loc:
    Eastern MA
    I'll jump on the draft bandwagon. I had some issues early on with my FV when it was warmer outside as well. My solution came in the form of an extra 3' of chimney added on top of my stack (I'm all class-A on the outside of the house). Once I did this I have not had any problems and I've also not had a single downdraft while lighting a cold stove either which I had experienced on those marginal days. Face it, the grand benefit of a cat stove is to be able to burn low and slow on warmer days - we really don't want to open up the air and burn hotter just to keep the draft open... So, consider options to improve draft, insulated liner, additional pipe on top, whatever fits your situation. It really may not take a whole lot, but could make running the stove a bit more pleasant.
  12. Joful

    Joful Minister of Fire

    Joined:
    Mar 7, 2012
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    6,386
    Loc:
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    I will look into lining the 8" masonry part of my flue with 6" steel, to improve draft. I do have a slate topper on the masonry stack, so it will need to be inserted from below, but I think it should be possible.

    In the meantime, or additionally, I need to learn a better process for getting from a cold stove to a long burn, particularly in warmer weather. I had been starting the stove with kindling, loading some medium splits in as soon as the kindling is going, then loading some larger splits in as soon as the mediums were burning well. As soon as I think I could, without killing the fire, I'd be engaging the catalyst. Likely this would be 15 - 20 minutes after starting the fire. Within 5 minutes of the catalyst lighting off, I'd be starting to reduce the air inlet, in a few small increments over 20 minutes. I have no stove or catalyst thermometers, and hadn't thought I needed either, but maybe it would help this beginner.

    As begreen suggested, my load was not completely charred over when I started lowering the throttle, but I see that taking a very long time. Long enough that I'd be burning a significant portion of the load, and making my room much warmer than I want, before I can get things slowed down for a long burn. Is this just the way it works, or is there a better way? How long should I anticipate running wide open before throttling down?

    I did try a much smaller fire last night, with two small'ish splits and two 3" branch rounds. 30% - 40% open on the air control, last load around 9pm, and the stove was still warm at 6am. That surprised me, as I thought I'd go thru such a small load very quickly with that amount of air inlet.

    Thanks.
  13. begreen

    begreen Mooderator Staff Member

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    Loc:
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    The slate topper will probably need to be temporarily removed for the liner installation, then reinstalled. See if there is room to install an insulated liner when getting estimates.

    The best way to know when to engage the bypass is with a thermometer. Although there is a provision for a cat thermometer on the back of the stove, that wouldn't help much due to the stove location. Instead use a good stove top thermometer. Shoot for about 500F on the stove top before engaging. Your procedure sounds pretty good as long as the wood is dry. It takes longer to engage the cat from a cold start than from a reload. So maybe allow it 5-10 more minutes before engaging. Note that certain species of wood take longer to start burning well; for example, white oak and locust. For quicker starts use dry 3" splits of ash, silver maple, alder, pine, fir etc..

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