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Wood Gun Gasification boiler "puffing" problem

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by glmccurdy, Jan 16, 2011.

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  1. glmccurdy

    glmccurdy New Member

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    This is my second year with a Wood Gun E-140 gasification boiler from Alternate Heating Systems. Back puffing has been a problem from the start. I installed a 5" round intake pipe for outside air, which greatly reduces the amount of smoke emitted in the basement, but that's only dealing with the symptom. The chimney is a 6" stainless steel liner with about a 50' run in a century old four story Victorian. The Wood Gun is connected to the chimney with the recommended configuration of stainless stovepipe. If I damp the standard wood stovepipe damper down on the fresh air intake side as far as it will go then it rarely back puffs. BUT, when it cycles on it will emit smoke out the 6" stainless flue side stovepipe that connects the ash collecting "cyclone" with the stainless chimney liner located within the brick chimney structure.
    There is chimney draft, but I have no means of measuring it. It sucks ash up pretty well. I connected a barometric draft control fixture up to the chimney pipe and, surprisingly, there wasn't enough draft to make the flapper move even when set at the lowest setting, even with the counter weight removed altogether.
    Perhaps it is worth mentioning that the is a creosote buildup in the air intake inlet (about a 5" round steel pipe) and, sometimes at least, the air intake stovepipe is warm within 6 - 8" of the boiler when the outside air temp is below freezing.
    I have read some other topics, and have gained the impression that I have a chimney draft problem, perhaps a column of cold air back-feeding into the "sealed" gasification unit that overpowers the thrust of the system's downdraft fan (which also acts to "push" air out to the ash collector/flue pipe. In part, my impression is due to the fact that puffing only occurs when the fire has been out for some time or the firebox has a one-half or more load in it.
    Any thoughts would be appreciated. In answering, it would be helpful if you defined any abbreviations used. I saw a lot of them in some of the other posts and have no clue what they mean. Is there a post that provides common definitions and acronyms? If not, maybe someone knowledgeable could post one.
    Thanks for any help.

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  2. begreen

    begreen Mooderator Staff Member

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    Moving this to the boiler room so that you will get a more informed response.

    First thing to confirm is that there is a good slope of the exhaust pipe at all points. It should have at least 1/4" per ft., but more is better. It sounds like there is negative pressure in the basement. Are there competing appliances installed there? Examples would be clothes dryer, bath exhaust fan, oil furnace/boiler, gas heater, etc.

    My other thought is that this is perhaps the tallest chimney I have heard of here. I'm wondering if the flue gases cool down so much that draft reverses? A measurement of the flue exit temps would tell this, though I'd guess that getting up there is not a fun thing. If this is the case a draft inducer may be the solution.
  3. glmccurdy

    glmccurdy New Member

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    Moderator - A reverse flow down the flue is possible, but I don't think so. There are a couple screw holes in the flue pipe between the boiler and the chimney structure, so they act as "blow holes" when there is positive pressure inside the pipe, which only happens when the fan for the gasification boiler cycles on.
    There is a clothes dryer in the basement, but that has never been a problem. I should note that the puffing almost always takes place under one of two conditions: (1) at night when the demand is less and the time between on-cycles is greater; or (2) when the outside temps are moderate (spring and fall, 40's, 50's, etc.) and the time between on-cycles is similarly long. The Wood Gun, I believe, has an unusually large ceramic mass that would have the effect of keeping the fuel load heated, thus producing gases and smoke in the firing chamber for long periods of time.
    Ah, one thing. I just cleaned out the Wood Gun and there is was a pile of ash at the back end of the gasification firing chamber (directly below the initial firing chamber). It shouldn't do that, and I have no idea why it does.

    I assume that a "draft inducer" is some sort of fan, but never heard of it before. (?). Thanks for the response.
  4. mikefromct

    mikefromct New Member

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    I cant answer your problem, but I can tell you my situation. I had an E-180 steel for 20 years, and now have an E-180 stainless and have always run it with the damper shut to avoid backpuffing. I dont understand when you say smoke comes out of the pipe connected to the cyclone - do you mean it sneaks out through the connections? I have not installed stainless yet, so I have used standard hardware store pipe replaced every 3 years or so - completely sealed with high temp. silicone, otherwise smoke sneaks out. In my experience, you cannot run these boilers with even a partially open draft. My inlet pipe is not vented outside, so any backpuffing at all causes the basement door to start shaking, and the smell would not be acceptable. So I shut the damper down so it only gets air through the center hole of the damper, or a slight crack around it and honestly, it runs fine. I also burn mostly larger pieces (approx avg 8" diameter) of wood seasoned only a few months. It takes a few years to learn what to burn and how to burn it but big and somewhat green is good for winter.
    My thoughts on your situation:
    creosote on the inlet pipe- have never seen it - perhaps the rubber gasket is not sealing properly on the inlet? The only creosote i have ever seen has dripped off the inlet valve.
    piles of ash inside- perhaps indicating the draft inducer (fan) is not doing its job? is there good suction through the center bricks? keeping them clear and open is key to good operation. I have heard of heat exchangers getting clogged and needing to be cleaned- maybe that causes a restriction in air flow. Taking the motor off and looking in there may show a clue.
  5. muncybob

    muncybob Minister of Fire

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    Running with damper completely closed....never done that. I have it partially closed hoping to use even less wood. I don't have backpuffing but lately I have noticed mine is "rumbling" now & then...a vibration from the boiler that can actually be felt in the floor boards directly above it. Sometimes I notice the pressure gauge fluctuating a few psi when it's rumbling. I'll be checking the nozzle tonight to be sure it's clear and may even play with the damper a bit. I recall when I first installed the WG that Carl at AHS said to run with the damper fully open.
  6. Der Fuirmeister

    Der Fuirmeister Member

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    Ex,

    I sent a reply below. Made a mistake on this reply and can't figure out how to delete a post in the edit.....
  7. Der Fuirmeister

    Der Fuirmeister Member

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    Ex, I have a SS E-140. I had a leaking pipe problem, but it was related to poorly sealed pipe joints. I've only had a small amount of back puffing once when I used way to much dry kindling and paper to get a fire started. Since then I use a sheet or two of newspaper, and half a small amount of card board on 2-4 splits. No dry pine at all. As mentioned in another response above from, everything I've ever read about back puffing seems to be related to wood that's too dry or starting a fire too fast. In any event, the fire is starving for air to burn the amount of available fuel. I run my SS E-140 with the intake damper wide open.

    Some questions and / or suggestions.....



    Did you run this down to the floor first? Running it up creates another chimney.



    Is much of that long run horizontal??? 50' of 6" may not sound like a lot, but the 180 is the largest unit that allows a 6" pipe. The E200 requires an 8". A long horizontal run would cool off the gases even more and add back pressure to the fan induced exhaust. Also, is the vertical run located in an outdoor masonry chimney (not surrounded by warm air)? If so the masonry is cold. I had this problem once with a small wood burning stove years ago. The air in the stove would flow out the door and it was very hard to get it lit. Here you have a fan, but it may be struggling to push against a cold chimney. If sealing the joints I would suggest using 600* rated silicone flue sealant on the joints or have a seamless SS pipe welded up.



    How often do you check your chimney for ash build up??? My fan is strong enough to load up my flue with ash in 2-3 months. When that happens I can tell from the sound that the fan is less affective.



    I hate to say this, but venting this outside may have added to the problem in two ways. This may help with the smoke, but longer runs reduce air flow / increase the vacuum on the supply side. If you really want to do this I'd recommend increasing the pipe size from 5-6" at the furnace floor and then running 6" pipe the rest of the way for less restriction. Also, by running the intake air outside you are now using cold air to light a fire instead of warm. The Garn unit pulls cold air through the hot water first to warm it up. Ice cold air does not help combustion as much as warm / hot air. I have no creosote at the intake on my E140. My 5" intake is never cold or hot.



    How much is a half load? If you mean half way up the fire box that's a full load. The same holds true for my Garn. These units are designed with a larger fire box for combustion, not for holding a lot of wood to get prolonged burn times. To quote the manual...."....start with a small load. Only fill after the refractory has reached good gasification temps...........best results with fuel loading will be obtained if the charge is limited to the amount needed to produce a 10 hour burn. Adding more will likely lead to build up and potential problems with back puffing....". And on another page it indicates....."Very dry wood creates a different problem.......The fire could then begin to release smoke....back puff".

    You'll get better burns with longer burn times by using larger splits, not more wood. I load with an average size 5" split. I never split smaller than 4". For overnight burns I use 6-8". And I won't load with a lot of small 4" pieces together. I get standing dead oak and split / burn it the same year. If I have really seasoned wood (two years old) I'll mix it with wetter wood. Another post here mentions using 8" cut / split the same year. The larger the piece, the less wood surface available for burning. Try loading with 3 or 4 splits (or better yet rounds) that are 8". An old timer once told me to mix my woods. That advice was for a stove, but it holds true for boilers as well if you have less than ideal wood.

    My guess is that there are several issues all adding up here. Without seeing it or know how the venting looks it's just a guess. I hope you take these comments as helpful suggestions.

    You have a really nice boiler. I hope you can get the rest of the system to work with it.

    Best wishes.
  8. Der Fuirmeister

    Der Fuirmeister Member

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    Bob, That rumbling is "surging". I had that at first. The pressure gauge bounces up and down. I read somewhere to throttle the ball valve between the system piping and the expansion tank slowly while it's occurring. I did that and it stopped. Smooth sailing with no problems since. The valve is about half open now.
  9. muncybob

    muncybob Minister of Fire

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    Thanks...will look into that. What exactly is causing the "surging"?
  10. Der Fuirmeister

    Der Fuirmeister Member

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    I don't remember what I read on that.........

    Maybe a post topic on that will get you some answers.
  11. Fred61

    Fred61 Minister of Fire

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    My take on puffing is that it is a self perpetuating phenomenon caused by wood that is too dry or any other fuel that burns rapidly. The fuel flares and quickly burns up the available oxygen and by the time it is replenished, excess gasses have been by produced causing the next explosion etc. Almost like dieseling. My observation is that it occurs when everything is perfect for combustion like hot refractory, hot boiler, excessively dry fuel and boiler going flat out. I have puffing periodically in my EKO. I think the answer is to mix wood with higher moisture content in with the dry stuff. Something I haven't dared to do while it is happening :bug:
  12. glmccurdy

    glmccurdy New Member

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    Thank you for the replies, folks. I have since installed an in-line draft inducer and connected it so it runs whenever the Wood Gun's fan motor turns on. MikefromCT runs his Wood Gun E-180 w/damper closed al the time. I'm doing that, too, and in combo with the draft inducer, that seems to work pretty well. As he and Dur Fiur Meister have both hit on the same issue - wood splits and rounds that are large enough and not too dry. AHS give very poor instructions on the fuel moisture content, leading one to the conclusion that it should be very dry. That apparently is not the case, and I will make sure to use wood with a higher moisture content. (I started out with kiln dried, and that probably precipitated the puffing problems). The learning curve on this sort of thing is really a lot steeper than I anticipated, and I see that as a serious limitation to the spread of the technology; too bad, but then most people are too lazy to want to tend a fire, anyway, let alone clean up the boiler.
  13. muncybob

    muncybob Minister of Fire

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    I'm approaching the end of my 2nd year and I'm still somewhere in that learning curve!
    I guess we don't get the puffing problems since our wood is not nearly as dry as your kiln dried wood. I seem to recall wood that dry really should be mixed with more moist wood to avoid the problems you have experienced. Last I checked most of our wood is around 20%...most of it is cherry that was cut&split; about 12 months ago. Seems to be working well...actually I'm using less wood than I expected considering we have had some failry cold periods lately. Good to hear you seem to have found a solution.
  14. rkusek

    rkusek Minister of Fire

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    Glad you found a solution. So much of this seems like trial & error, finding out what someone else does that works well.
  15. Der Fuirmeister

    Der Fuirmeister Member

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    Please let us know if you need any further suggestions. You can send me a PM (private message) any time and I'd be happy to help. Just click on the PM button at the top of the page. BTW (by the way) I've been burning wood most of my life and I'm still learning new with these new boilers (same for computers). Back in the 70's we used to throw anything that would burn into a Ben Franklin replica stove! I kid you not.
  16. chiefburritt

    chiefburritt New Member

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    I too would get the occasional puffing when my wood was too dry or when my primary chamber is full of "charcoal". If you don't clean the primary chamber on a regular basis of the "charcoalized" wood then the amount of surface area of combustion exceeds the supply of fresh air. Since I run a steam system I dont have the luxury of lighting a fire and having it burn out. My fire is lit 24/7 and the system runs as the stat calls for heat, so after or during a prolonged cold spell the charcoal and ash will build up in the primary chamber and create a puffing situation.

    I have come to realize letting the entire charge of wood burn almost out will consume most of the charcoal created in the primary from the idling time that I must have to have. Sometimes I have been caught cold that way though. If this isn't your case then maybe your 40' of stack at 6" is pushing the limit of the fan. I also use a high temp silicone to seal the flue joints.
  17. PADCNRForester

    PADCNRForester New Member

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    Hello everyone, I just signed up with the hearth.com chat forum. We installed an Alternate Heating Systems E-140 stainless steel wood gassification boiler with oil backup in the fall of 2010. The unit replaced our former heating system which consisted of an ancient Burnham B17 soft coal boiler, and an equally ancient American Standard oil boiler as a backup. First I would like to say that the AHS wood gun is a great unit. It has worked well for us this winter, and the additional capability of heating our domestic hot water has taken a nice chunk out of the electric bill. Since we already had a hot water system with the old-fashioned cast iron radiators, the Wood Gun was a great fit. That being said, with any new appliance there is a learning curve. We did not have the stove pipe joints sealed with the high temperature silicone when we first fired it up, and had an instant smoke-house in the basement. Red RTV high-temp sealant took care of that problem. We also had issues with some back puffing at various times, but it seems if you keep the unit clean, don't load too heavily, and let it keep the charcoal burnt off, things seem to work well. I do keep the damper almost closed, and super dry wood is probably to be avoided or mixed with some that has a higher moisture content. We also have issues with the purge timer not working properly, and the green indicator light quit coming on that indicates the air valve is open and the fan is running. The loading door also dripped creosote, but I adusted it and that problem was solved. Also, if you don't use the oil backup burner once in a while it will not light and you need to reset it. You probably should fire it once a week if you expect it to light reliably. I plan on only using it in the spring and fall, so I can just get it working for those times. We are using conventional stovepipe to connect to the chimney, and there is a good angle to it. One thing we probably will change is that we have an angle joint immediately above the cyclone, which is not reccomended by AHS. For the next heating season I plan to change the stove pipe to straight runs with T connectors with clean-outs on them as recommended, and see if that makes any difference with the puffing issues. I do have one question for everyone in general, and that is where can I find the straight pipe and T connectors, preferably stainless steel, to make this change? Thanks in advance to all replies!
  18. chiefburritt

    chiefburritt New Member

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    A local metal shop made mine for me out of stainless steel and it still looks like new.
  19. muncybob

    muncybob Minister of Fire

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    We also had problems with the "green light"...narrowed it down to the Honeywell unit on the back that controls the air intake flap. At first they said it was the old style bulb but there was nothing wrong with the bulb. I would get that part swapped out if still under warranty. Insist that they check the replacement unit at the factory though, we went through 2 more until they sent me one that worked properly...no problem since.

    We were just going to wait 1.5 to 2 minutes after the fan starts running but Carl at AHS insisted we get it working properly.
  20. mark123

    mark123 Member

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    I have a 180 and have come to the conclusion that dry wood is the culprit of the back puffing problem. In the late fall I could fill the box with moist wood which was just put inside. My wood/boiler room is approx 90 F and as time went on the wood became extemely dry. I use all round maple 4"-10". I called Jeff at AHS and he said they are working on some modified air intake tube but have not perfected it yet. The idea is to have to air go more directly to the slotted refractory and not into the entire firebox which should prevent the fire from raising higher into the woodpile.
    He mentioned closing the air damper but wouldn't this also significantly lower the BTU output of the boiler. My puffing has gotten so bad that it actually blew my intake ductwork apart. I have approx. a 25' run of 6" metal ductwork one night we heard an explosion in the basement. One 5' length completely blew apart and the insulation all split open. When it is puffing the whole boiler starts moving back and forth. I used to have 4" and the puffing was not as bad but it was likely due to the long run restricting the airflow similarly to closing the damper somewhat. I hope they come up with some add on solution because it was nice filling the box and not going back down for 10-12 hours. Now I can only keep the box approx 1/3 full. The funny thing is that if I open the door and bit the puffing stops, doesn't this mean it is starving for air.
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