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Is one stove design more prone to runaway than another?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by metalsped, Dec 22, 2012.

  1. BrowningBAR

    BrowningBAR Minister of Fire

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    Also, I can have the Defiant shut down all the way and the temps will climb to north of 750 if I let it. I've altered the primary air to allow me to completely close down the primary air when this happens.

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  2. fox9988

    fox9988 Minister of Fire

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    On my chimney, I can pack the firebox and cruise as low as 400::F.
  3. rideau

    rideau Minister of Fire

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    Woody,

    I said the PH was much more controllable than the Fireview, which itself is very safe and controllable. I believe both present very low risk for true runaway fire.

    I'm assuming all cases of overfiring of a well designed stove are caused by operator error.

    And certainly in my case operator error has occurred because of distractions when loading the stove initially, not from leaving the air open while in a cat burn, or from trying to get too much heat from the stove. I'm very conservative in the temperatures I fire my stoves. Dennis, for instance, scares me! Although I know he knows what he's doing.:)

    I have been distracted and left my bypass open too long on both the Fireview (perhaps three times) and PH (once).

    On the Fireview, you have very little time from the stove going from not yet ready to engage cat, to a really hot stove. I have never "overfired" my Fireview, but several times got it a lot hotter than I like, and to where I can smell the heat..temp on stovetop over 650. It always calmed down when I closed the air, so was never runaway, but I would have a very active fire for up to twenty minutes before the flames died completely. During that time, though, there would be no significant rise in temperature. I always felt that the stove could easily get a lot hotter very quickly if left longer with the air open and the cat not engaged. I would note the Fireview takes a good half hour to get to operating temperature.

    On the other, the PH gets to a temp where the cat can be engaged in ten to fifteen minutes. And, the PH can develop a roaring fire if you load on a large bed of coals, delay engaging the cat for a bit and keep the air half open, and the stovetop temps will still be around 300. The flue temp will still be in a safe range. And when you close the air, the fire dies down almost immediately. It is more forgiving of operator error and harder to get to really high temperatures, likely because the secondaries engage as soon as the stove gets good and hot even if the cat isn't engaged, and tons of heat comes out the (much larger than Fireview) window quickly, instead of lots of heat going up the chimney and into the soapstone.

    So, I would say both stoves are unlikely to be have runaway fires, but I believe it is possible on the Fireview with real operator neglect (if you left the air open, cat unengaged for 45 minutes to an hour?) but very unlikely on the PH. I've never gotten mine over about 525, even when trying to get a really hot fire going, and having the stove crank out remarkable amounts of heat. Higher the stove top temp, lower the flue temp, and stovetop never anywhere near overfired range.

    Sorry to be so wordy, but didn't want to leave a wrong impression about these great stoves....
  4. Beetle-Kill

    Beetle-Kill Minister of Fire

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    Aww crap, overfires happen. Operator error has to be 99% of the problem, 'cause the stoves don't load nor control themselves.
    I'm as guilty as anyone of letting the flue temp. go north of the "safe" zone.
    I just try to learn from my mistakes. It happens.
  5. Machria

    Machria Minister of Fire

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    Very nice to know, as I just finished my 3rd small burn. Amazing how much heat the PH puts out.
  6. ddddddden

    ddddddden Minister of Fire

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    Hmm. . .I didn't really mean to take the ol' cat vs. non-cat tone. . .thought that war was over, and The Aliens won.;lol Runaway is futile. Your combustion technology will be assimilated by the BKollective. . .

    But seriously, I thought we had reached consensus on the basic characteristics of the two main types of design, and I read OP's Q as a general one about design rather than specific stoves.

    There are adaptations and work-arounds, but it seems to be more of a non-cat issue, because EPA regs interfere with the design.

    http://www.gulland.ca/florida_bungalow_syndrome.htm

    http://www.hearth.com/talk/threads/florida-bungalow-syndrome-comments.13191/
  7. Woody Stover

    Woody Stover Minister of Fire

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    You just like the adrenalin rush of the occasional moon-shot runaway. You're a born thrill-seeker, like the suspenders bungee jumpers. ==c
    Guns don't kill people; Bullets do.
  8. MnDave

    MnDave Guest

    After over a decade of using a non-EPA stove in this house, I switched to an EPA non-cat stove.

    With the old stove, a few times I accidentally left the air control open too long on startup. Luckily I was always in the house and could smell that the stove was too hot. I would occassionally find the stovepipe temp had hit 600F, 650F one time. I would close the air control completely and this would extinguish the flames entirely in a matter of minutes and let the stovepipe cool. I have a Class A chimney so this did not damage anything.

    With the new EPA stove I used the same 22 foot chimney but I added an OAK to help the startup as I used to have problems when the dryer and/or the water heater were running.

    The Quadrafire 5700 with 1/2 loads or so behaved reasonably well on the minimum burn setting. However, I was already noting that the wood was burning very fast and the temps were in the middle of the burn zone. I thought it was just that my wood was especially dry.

    I then tried a 3/4 load of 4" splits of dry mixed wood. When the entire load ignited I knew it was time to take action. I moved the air control to minimum and disengaged the ACC (Automatic Combustion Control). The stovepipe gauge crept up to around 550F (top of the burn zone). Again, that was after reducing the air as much as possible. The temps would not come down for over an hour until the gasses started to drop off. I know that this was not a safety issue but it sure surprised me. My definition of runaway... when the operator cannot get control of the burn rate.

    So with the new stove I ended up putting a stovepipe damper in. This made a huge difference in how much control I have now. The damper allows me to prevent too much of the wood from igniting all at once. IMO, without the damper, the entire load will ignite, even when starting from a smaller coalbed pulled to the front.

    For me the damper was the key to using this stove efficiently. I can now load 1/2 full, set the ACC, set the burn rate and damper, and walk away with confidence that it will not overfire. When I fully load the stove for an overnight burn I stick around to make sure it lights well and to learn more about how different ways of stacking the splits in this stove affect the startup.

    I really do not know how a cat-stove would handle a large load that fully ignites. It seems like the cat would act like a stovepipe damper and regulate the burn rate. Hopefully it would not just act like a blow torch and run up the stovepipe temps. I have no first hand experience with cat stoves so I cannot comment on their propensity to runaway if the whole load ignites.

    So to answer the OP's question, IMO, an EPA (non-cat) stove design is more prone to runaway than a non-EPA design.

    This is because the EPA design does not let you choke off the air like in a non-EPA design.

    I discussed my damper with my Quadra Fire salesman. He said that his installers use them but that Quadra Fire does not think they are needed.

    MnDave
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  9. HotCoals

    HotCoals Minister of Fire

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    On a cat stove if the cat is hot it will create more draft in the stove and therefore burn the wood a little faster.
    The cat stove I have will never run away as long as the operator does not do something stupid like leave the door ajar or leave the air way open.

    If I load her up burn 20 mins on med-high..then shut the t-stat to 2 or under with the by-pass shut this stove will not runaway no how, no way.
    MnDave likes this.
  10. charly

    charly Guest

    So far my Fireview seems like it could never run away with the cat engaged along with a proper low draft setting... With the by pass open,,,,,she gets the chimney up to temps quick,,, which I don't mind,, as that avoids a cool chimney for a long period during a reload, resulting in a cleaner chimney.
  11. Machria

    Machria Minister of Fire

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    Actually, the stove pipe and flue temps go down when the cat is engaged, it burns up all the heat and delivers it to the stove(and surrounding area), instead of it going up the pipe.

    I'm not sure what you mean about that, but when the CAT is enganged, there seems to be less draw on the draft and the fire in the fire box slows down. The wood is then burned slower, not faster. It's also burned more efficiently since all the smoke and gasses not burned by the secondaries are burned by the cat. That's on the PH anyway.
    raybonz likes this.
  12. HotCoals

    HotCoals Minister of Fire

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    On my stove if the cat stalls the wood will last forever..had it happen a few times from not charring the wood enough before closing her down for the night.

    A hot cat will pull a little more.
    But still there are no flames from the wood when the t-stat is closed and the cat is glowing away.
    But the orange glow from the bottom of the stove is brighter when the cat is cooking.
  13. rideau

    rideau Minister of Fire

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    When the cat stalls the wood is lasting forever because the cat is not burning anyhting and the stove hasn't enough air to burn the wood in non-cat mode. You have a smouldering at best fire, which produces lots of creosote.

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