Puff Backs

 
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lowfog01
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Post by lowfog01 » Wed. Nov. 04, 2009 7:59 pm

Hi guys,

I'm having a major brain fart - I am getting some pretty good size puff backs during my evening service for the Mark II the last couple of days.

First, I open the ashpan door and refresh the fire while I'm emptying the previous service's ashes; two or three minute’s tops. Second, with the fire burning well I close the ashpan door and prepare to shake the stove down. Tonight the blue ladies mostly went away as the ash door was closed but reappeared within a couple of seconds with the puff back. Last night the ash door was still open when the puff back happened.

What am I missing here? Both nights after the puff back the blue ladies resume their dance and I shake the stove. Then I add new coal with no further puffback. The stove top temp is 200* or 175* - I'm idling - and the draft is good but I've not got my manometer installed yet. Could gases be forming with the low draft of the idle? That would seem weird because the draft is actually better now than it was last week because of the colder weather. It didn't do this last week.

I didn't witness the puff back last night but my husband did and it bothered him enough for him to check the stove pipes - yes, they are attached with at least 3 screws. I saw tonight's puff back and even though the doors were closed it was strong enough to create a cloud of flyash. I'm open for any idea of what I’m missing and solutions to stop it. Thanks, Lisa


 
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gitrdonecoal
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Post by gitrdonecoal » Wed. Nov. 04, 2009 8:23 pm

Loading too much too fast??? I know this has happened to me when I would be in a hurry to leave the house. Once I had a puff back so big ash sprayed out of the asp pan cavity 6 feet. Just an idea

 
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SMITTY
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Post by SMITTY » Wed. Nov. 04, 2009 8:30 pm

Even though it may be colder than before, it's still not "cold" out quite yet .... especially in VA. So your draft isn't 100% yet ... especially with a low or idling fire. That, & you might be covering the hot coal with fresh coal just a bit too much as gitrdonecoal mentioned. This usually happens to me when I first light the stove for the season & it's not quite "cold" out yet ... or if I'm in a hurry & just pile the coal on.

 
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Post by coaledsweat » Wed. Nov. 04, 2009 8:33 pm

Rev it up good before you shake and then bank the coal before reloading. The more flame you have on the surface of the fire, the less chance you have for a puffback.

 
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Razzler
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Post by Razzler » Wed. Nov. 04, 2009 9:18 pm

coaledsweat wrote:Rev it up good before you shake and then bank the coal before reloading.
As Coaledsweat said get it glowing orange not just the blue flames, then when you reload leave a corner open to the hot orange coals so it burns off the gas. ;)

 
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VigIIPeaBurner
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Post by VigIIPeaBurner » Thu. Nov. 05, 2009 12:16 am

Might need to open the air up a bit before you do your procedure under current weather conditions. Reset them after the fire/draft is re-established from reloading. I've had similar experiences but mine is a top loader with a thermostatically controlled air inlet that I don't usually fool with because it opens as things cool automatically intoducing more air. Instead, when I see the dancing blue ladies sit down after closing the ash pan door, I cautiously crack open the top loader and blow into the top of the firebox. Poof~ they get back on the floor and start dancing.

Thinking this one through as best as I can, I think that what is needed is more oxygen over the fire entering from under it via the usual route. Keeping a corner open like Razzler said helps this to happen. I might be right and then again, I might be wrong. The Holiday Inn effect :oops: There's plenty there when the ash pan door is open but oxygen concentrating drops off when it's closed. The draft falls from the cooling effect of the new load of coal. The methane isn't pulled up the chimney and consequently enough fresh air isn't pulled into the firebox through the inlets when set at the old/previous opening to burn it off. The methane builds above the load in the firebox more quickly than the air opening supplies the required oxygen to keep the dancers on the floor. The two components for combustion build until they reach the levels required for combustion ...
  • POOF!

 
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Post by Freddy » Thu. Nov. 05, 2009 2:26 am

I think coalkirk hit the nail on the head. If you bank the coal before you rev it up or shake it down,...that is, move it on one edge so there's fire showing on top in that spot. it may solve the problem. When you rev it up it is heating unburned coal that's on top. That releases voltile gasses. The next time a flicker of flame makes it to the top, *poof!* So, if the coal were banked, it would have a constant flicker at the top, thus burning those gasses as they are formed, rather than collecting them for a poofy ignition a few minutes later.
And...or...perhaps there's a different nail to drive.....maybe this time of year don't fill the stove as much? The idea would be that when you go to service it there would a near solid red surface instead of a layer of unburned coal on top.


 
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Post by lowfog01 » Thu. Nov. 05, 2009 4:28 am

Thanks for all your thoughts. They have all given me ideas and things to try to prevent this from happening again. Thanks again. Lisa

 
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Post by titleist1 » Thu. Nov. 05, 2009 7:10 am

I agree with the "hot corner" method. I get the fire rev'ed up prior to loading keeping the ash pan door open for a bit then load it with coal except for a corner where I keep it clear to allow the glowing coal to show through. I keep the ash pan door open for about 5 minutes after loading, carry the kitchen timer if you do this. This keeps the blue flames fed on top of the new coal burning off the volatiles and keeps the little booms from happening. If I am around to mess with it, I'll cover that corner with coal in about an hour, if not, it stays the way it is.

Disclaimer....I am writing this from memory from last year since I have not had to fire up yet. The few cold days we've had have been remedied by an afternoon wood fire that I let burn out through the night. Although I heard the furnace kick on this morning around 5 so I will probably start up the first coal fire this evening.

 
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Post by CoalHeat » Thu. Nov. 05, 2009 8:17 am

I've had the same thing happen, Lisa. Add the fresh coal slowly, in stages, let the new coal catch in between. Leave an area of burning coal exposed, I load the coal into the stove on the back and sides, leaving burning coal exposed in the center front. Also, since we don't need lots of heat yet there is a tendency to cut the air intake down too low too soon. Leave the intake vent open wider for a little while until the new coal is burning and adjust the windowstat as needed. I'm running the Mark I at 1/2 to 3/4 a turn open right now.

We're always learning, me too:

Minor Explosion in Coal Stove

 
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Post by franco b » Thu. Nov. 05, 2009 12:00 pm

To burn the gasses they need to be hot enough and have air in a timely fashion. Do your normal thing only this time crack open the top door. If the blue flames instantly appear, then obviously there is heat enough. If this is the case then you might consider adding secondary air. You can do this by drilling a few 1/4 in holes, probably near the bottom of the door. Tap for 1/4 x20 so you can easily close them if you so choose. Start with maybe 3, one centered and two a few inches from the sides. Too much secondary air raises stack temperatures and steals draft from under the fire, and too little leads to waste of fuel and to the conditions you experienced. The problem is that the balance of primary to secondary air shifts all the time based on the stage of the burn, depth of bed and draft setting. So everything is a compromise but I would not allow the condition you describe to continue without doing something.

Richard

 
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Post by lowfog01 » Thu. Nov. 05, 2009 12:31 pm

Thanks for all the input. I'm thinking the concenus is that the I need more over the fire air - at least at the time I'm tending the fire - to help the draft pull the gasses up and out. I think I'll crack the loading door a little between shaking the fire down and actually loading the coal. That way the gasses won't build up. I'll also make a more concerted effort to ensure a flame is present in the corner as I add coal. Hopefully, the puffbacks will be a thing of the past. It is strange though, because I do the same thing in the morning with no puffbacks. Maybe that's because of the cooler air of the early morning?

Boy, who knew when I started looking at coal as a supplemental heating source that I would be undertaking a life long learning opportunity. :D Thanks for your help, Lisa

 
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Post by CoalHeat » Thu. Nov. 05, 2009 4:54 pm

I don't know how strong your chimney drafts, but mine pulls like a bas--, uh, bear. My baro runs about 1/2 way open with a full fire, I try to keep the draft around -.04" WC.
BARO 01-20-08.jpg
.JPG | 40.2KB | BARO 01-20-08.jpg
When I'm bringing up the fire before shaking, during shaking, and during reloading I wedge the baro shut, the added draft makes the whole procedure a little easier.

 
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Post by titleist1 » Thu. Nov. 05, 2009 6:16 pm

regarding the overfire air...
Before you start drilling and tapping holes in your stove, do you have the glass on the front of your Harman? If so, do the panes of glass have some play in them to allow air to enter the firebox? They should not have the rope gasket all the way around them and they should not be clogged with ash. If they do maybe that is the reason for the lack of overfire air.

 
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Post by tsb » Thu. Nov. 05, 2009 9:11 pm

Is your coal the same as last year ? When I changed to
southern range coal, my hand fed got a little farty at times.
After I shook the stove, I would get a pretty good wooooof when
I opened the hopper to load. Even when just burning it tends
to fart and carry on at times. I just got used to it.

Tom


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