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  1. coltfever

    coltfever Member

    Joined:
    Jan 4, 2011
    Messages:
    115
    Loc:
    Middle Tennessee
    I have a question to why I get a huge slow motion rolling fire burst of flames and very quick puff of smoke comes out of the primary air slide on the lower front of my stove door when I closes my air all the way shut. It looks so strange when this happens. Make the house smell smokey too. My stove is an Appalachian 52 Bay ( cat insert ) The way you adjust the burn there are 2 primary air adjustments on each side of the door that lets air flow up inside the door and out through these little holes at the top for the door for the air wash. This only happens when you close the air off all the way and loaded the stove with wood. Am I starving the stove of air ? If you open the air just alittle no problem. This stove is new to me and I am in the learning process. I have read my stove manual and follow what it says. Wood is 2 year old seasoned and I wait for my cat temp to reach 600 to 700 before I engage. The only thing I can think of that I might be doing wrong is I'm closing the air off to quick.

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  2. peakbagger

    peakbagger Minister of Fire

    Joined:
    Jul 11, 2008
    Messages:
    1,948
    Loc:
    Northern NH
    Yup you are starving the stove of air. Any stove is pretty simple, wood doesnt burn, wood gas does. If you load the stove on some hot coals, you are generating all sorts of wood gas. At some point with an air tight stove, you run out of oxygen and the stove and chimney fill up with volatile gas that cant burn or only partially burns as there is not enough oxygen. When you open the door, all that hot gas lights off rapidly.

    Running a stove the way you do, filling it up and then controlling it with air flow is not a great way to burn but many do as it extends the period of time between having to feed it. A sotve without a Cat will tend to form a lot creosote when run this way and will tend to pollute. A Cat might help a bit but it also needs oxygen to do its thing. Most of the new EPA stoves have hidden air ports so that if the owner decide to shut off the primary ports, the hidden ones ensure that there is enough air to keep burning. Problems with backpuffing tends to be in the shoulder seasons when the stove has far more capacity then needed, so the owners try to throtttle them back. The right way to do it is to make small fires and control the output by controlling the fuel and letting the stove go out. By the way, the other benefit to running the sotve correctly is that the neighbors will appreciate the major reduction in wood stove smell.

    An automotive comparison is that trying to control stove by cutting off the air is the equivalent of pouring enough fuel into the engine to run at full speed and then controlling the speed by controlling the amount of air that goes into the engine. This wastes a lot of fuel and puts out all sorts of pollution.
  3. Jags

    Jags Moderate Moderator Staff Member

    Joined:
    Aug 2, 2006
    Messages:
    15,991
    Loc:
    Northern IL
    Yes - you are starving the stove for air. Find the sweet spot just above this setting and you should eliminate it. And it SHOULD be eliminated. The current setting that is causing this is really not where you want to be. Leaving primary air 1/8th to 1/4 open for cruise speed is very common on many stoves.
  4. Slow1

    Slow1 Minister of Fire

    Joined:
    Nov 26, 2008
    Messages:
    2,665
    Loc:
    Eastern MA
    Something I learned with my FV which may or may not apply across other CAT stoves is that if the firebox is too hot and the air is shut down quickly it will more likely backpuff. The other major factor can be the draft - i.e. if you don't have a very strong draft then it can't pull enough air through for the given setting. Either way the solution is (as stated already) to give the box a bit more air. I only had major issues during shoulder season when my draft was weak - I fixed that with 3' of additional pipe at the top. After that I would sometimes get minor 'poofs' in the box that were more annoying than anything unless they got big enough to push smoke into the room.

    In any case, if you still want that lower burn with the large pile of wood in the cat stove, try and keep the firebox from being quite so hot when you engage the cat and shut down the air - i.e. once you engage the cat get that air going down right away (depending on how stable you can keep the cat from stalling). If you let the box keep heating up it will produce ever more woodgas to burn off and eventually it may get ahead of you.

    You should be able to fully load a cat stove and run it at a lower temp with some care and planning, but remember nothing really happens fast in the firebox so small to medium adjustments are generally better tolerated and allow the lag time to catch up with you before you conclude your adjustment has taken full effect.
  5. raybonz

    raybonz Minister of Fire

    Joined:
    Feb 5, 2008
    Messages:
    6,211
    Loc:
    Carver, MA.
    With the CDW I also found that burning a lot of small wood can cause this as well.. Really hated the backpuff thing especially hated the smell of oak! I managed to improve the backpuff issue by being more careful but on occasion it still did it but it was a rare thing. I don't think you could ever completely eliminate backpuffs on a cat stove but you can substantially reduce them by using dry wood, carefully control the air, rearranging the wood in the stove and using larger splits.

    Ray
  6. Slow1

    Slow1 Minister of Fire

    Joined:
    Nov 26, 2008
    Messages:
    2,665
    Loc:
    Eastern MA
    I don't think that backpuffing is unique to cat stoves - and I do believe that, at least in some models, you can essentially eliminate them. I had a few issues when I first started burning my FV (during the first few weeks), but I don't recall having any for the remaining three years that I owned that stove. And I don't believe I did anything particularly unusual to avoid them - i.e. they were not on my mind during the operation of the stove.

    Now I'm playing with the new PH and I might have had one (something happened when I wasn't looking) but I'm willing to take the blame if it did - I spent the weekend playing with the air control moving it from max to min (and back again.. and again) to see what it could do and rather expected some "interesting" results.
  7. raybonz

    raybonz Minister of Fire

    Joined:
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    Loc:
    Carver, MA.
    Haven't seen a back puff on the T-5 yet going into 2nd season. Can't recall hearing anyone with secondary burn back puffing here either. Think this is because the cat adds resistance to the flue gasses and can't keep up in certain conditions but I could be wrong. The PH is unique in that it is a hybrid so this could help prevent this from happening? Not throwing stones as I have burned both types now.

    Ray
  8. raybonz

    raybonz Minister of Fire

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  9. Jags

    Jags Moderate Moderator Staff Member

    Joined:
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    Loc:
    Northern IL
    I'll be your huckleberry. Had a HUGE one that I thought was going to blow the stove to the basement. Totally my fault. The BVDs took a direct hit too.:eek:
    raybonz likes this.
  10. raybonz

    raybonz Minister of Fire

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    Feb 5, 2008
    Messages:
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    Loc:
    Carver, MA.
    LOL Jags you explain that one! Was this a cat or 2ndary burn stove and what caused it? Seems my CDW were much more prone to puffs in shoulder season but they happened at other times for whatever reason too..

    Ray
  11. Jags

    Jags Moderate Moderator Staff Member

    Joined:
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    Messages:
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    Loc:
    Northern IL
    Secondary burn tubes.

    If you ever see me reinforce the thought that you should NEVER use an ash pan door for startup air - well, thats the story.
  12. raybonz

    raybonz Minister of Fire

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    Carver, MA.
    OIC a definite no-no! I have an ash chute to dump ashes to the ash pan but never use it. Door stays closed unless adding wood as it starts great with full air..

    Ray
  13. mellow

    mellow Resident Stove Connoisseur

    Joined:
    Jan 19, 2008
    Messages:
    3,887
    Loc:
    Salisbury, MD
    Just did see this thread, I had the same issue last year and posted about it: http://www.hearth.com/talk/threads/cat-stove-question.86305/

    Get a good bed of hot coals before you really turn down the air with a good fire going, I have found I have to leave a little flame action going on or I get blow backs as well.
  14. Treacherous

    Treacherous Minister of Fire

    Joined:
    May 13, 2010
    Messages:
    978
    Loc:
    WA state
    The only time I ever had some backpuffing was on my old Centennial smoke dragon when it was really cranked down.
  15. Backwoods Savage

    Backwoods Savage Minister of Fire

    Joined:
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    Messages:
    27,815
    Loc:
    Michigan
    Is this thread for real or just a come-on. The OP answered his own question!
  16. Cross Cut Saw

    Cross Cut Saw Feeling the Heat

    Joined:
    Mar 25, 2012
    Messages:
    404
    Loc:
    Boulder, CO
    I just had my first backfire tonight.

    It was supposed to be a warm day today (50 degrees) so I only did a small fire this morning (5:30am) for my wife, it was in the 30's most of the day and felt like it was getting warmer this evening. She said she added a little wood to it around 3pm since there were only very few coals left in it and it was getting a little chilly. By the time I got the kids to bed at around 8 I loaded in about a 60% capacity load, waited til it was well lit (15-20 minutes) and the stove top temperature was about 400 degrees before lowering the air to about 1/3 and closing the bypass.

    I watched the temps and slowly closed the air down all the way over the next half hour or so and it was hovering around 500 degrees every time I looked until I was getting ready for bed. So around 11pm I'm getting ready to go to bed and glance at the stove on my way by and it's at 570 degrees and I hear POOF, thinking that's weird I go around locking doors and turning off lights and realize I can smell smoke.

    Just like I do when anything "weird" happens I come on here and then google to see what people suggest I do. I opened they bypass because the temperature had quickly risen to 600 degrees in a matter of a few minutes and give it a little air since it was closed all the way.

    It quickly cooled down to 570ish before I closed the bypass again and left the air open a crack.

    I think the weather may have played a role, it got very breezy and much warmer as the night went on, it's like 51 degrees in the middle of the night in December!

    Here's what I read about backfires somewhere else, I especially like the part about seasoning your wood for 10 days:

    "It happens because it's very smokey in the stove so you probably have the flue shut down. Simply open the flue some so you have a better flame rather then a smolder so it burns cleaner. Also have your chimney serviced at least once a year, try to burn seasoned wood (dry). Remember if you split green wood bring it in the garage 10 days later or so most of it's moisture content is gone and it's ready to burn."
    raybonz likes this.
  17. MnDave

    MnDave Guest

    uuuuhhhhhh. We all know it takes at least 15 days to season wood to perfection. 10 days if you keep the car running.

    That's a keeper.
  18. Ashful

    Ashful Minister of Fire

    Joined:
    Mar 7, 2012
    Messages:
    7,519
    Loc:
    Philadelphia
    I've unfortunately been forced to become an expert on backpuffing over the last year. Most of the time it's just annoying, putting smelly smoke into the house, but occasionally it can be disastrous. I do know one local family who had the doors of their stove blown open by a violent backpuff, throwing flaming coals all over their living room. There was a fire, but they were home to catch it, and the house was saved. I've read other similar stories online.

    The answer is "more air." If that means your stove runs too hot for the circumastances, then the compound answer is, "more air, less wood."

    Increasing draft, by insulating or increasing the height of your chimney, is said to help. However, my experience with one stove (and my intuition) says that this cannot really solve the problem completely. More draft = more heat, so while you may be able to physically close the air control all the way by improving the chimney draft, the net result is likely the same as just leaving it cracked a bit before you insulated or extended the flue.

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