Outdoor Wood Furnace Info
Outdoor Furnaces - Manufacturers WITH EPA-Certified Models => Portage & Main => Topic started by: TheSnowDO on January 13, 2018, 09:25:54 AM
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This is the fourth season I have been running this unit and I keep having the same issue with keeping it gassing. Burning various types of hard wood only, that has been seasoned for a year in 16' sections. I only split the stuff that is too big to handle if left whole. I always position the biggest pieces over the nozzle and try to keep a healthy 6-8" of coals in the bottom of the burn box (which has been difficult). I am a heating a poorly insulated (will hopefully be sealing it up this coming year) 2700 sf old victorian (1904) in the Adirondacks.
I have no problem getting the unit to gas, but keeping her up to temp has been very difficult. She seems to do long runs and she seems to power through the coals directly surrounding the nozzle creating this funnel type path to the nozzle and I also get this tenting that occurs over the nozzle that in the past has actually burned through the middle of the larger log that I positioned over the nozzle creating about a 12" empty space that funnels down to the opening of the nozzle and THEN she STOPS GASSING and my temps plummet. I can get her gassing again simply by going out and stirring the coals around which won't even last long enough to get her back up to temperature before it starts tenting again.
I have set the air box settings according to recommendations from SlimJim and other old timers on this site but still wonder if I have too much air moving through the fire box that it burns everything on its way to the nozzle ????
Anyone else having similar experiences?
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Wood doesn’t dry in log length. I would suspect it is very wet for one thing. Also gassers don’t burn rounds well. You will need to start splitting everything into 4-6 inch diameter pieces and expieremnt with smaller and larger pieces.
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Honda is correct. I have the same unit and am in my 4th season as well. Rounds are terrible to burn. I split anything over 4" once. I also process 2-3 years ahead which on certain types of wood may be too long but I figure if for some reason I'm not able to cut one year at least the wife will not have to worry about it. You might also try to stack the wood in so it may collapse in toward the nozzle and not fall toward the sides of the firebox.
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Cabo has real expierence with your model. I only have expierence with a g200 but the principles are the same.
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I have never ran your boiler but what you are describing is tenting caused by the wood on top of the coal bed not breaking down to coals fast enough to replenish the ones being used up. It is all a cycle. The coals need to break down the wood on top of them to wood gas and coals. If the wood is o wet, to large or doesn’t have good contact with the coal bed then the coals will be used up before they can break down the wood. You can work to fix this by splitting your wood smaller to help it have more surface area and break down faster. Do you have a moisture meter to check your wood mc?
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Honda has sound advice. I would try splitting some of your wood into smaller pieces to see if it coals up better and collapses more readily into the nozzle. I have found that too much primary air also causes it to bridge more readily. With my 250 you can really cut down on the primary air and keep it gassing if your wood is dry enough. Too much air with dry small splits will cause it to backfire and whoosh as it begins to burn up instead of down. You really only want enough air to keep it smoldering and breaking down instead of burning upwards in the firebox. It will burn larger rounds and wet wood, but it will need a lot of primary air and it will have a tendency to bridge and not coal.
What are your restrictor plate, primary air and secondary air settings?
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Im on my 8th year with a 250. I would try not keeping as much of a coal bed. I put my biggest wood directly over the nozzle and then stack around and above that. I really think too much of a coal bed is your problem. Hope this helps.
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Karlk. What size are you splits and how well seasoned? His wood has been in 16 foot logs up until now and he doesn’t split it unless he can’t handle it.
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I agree with Karla, these boilers don't need a big coal bed, Honda is correct to split your wood smaller.
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I will split a 8-10 inch log in half. Im sure his wood is wet but i have already ran out of wood and cut standing dead red oak and used it right away. Its not the best but it works.
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Karl. Do you mix smaller and larger splits? How about your coal bed? How deep do you run that?
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It depends on the temp, if its real cold I use just big splits, but warmer days I put on 1-2 larger splits the the rest are smaller. I try not to have much of a coal bed.I think it acts as an insulator and keeps the refractory floor cooler than it could be. I try to clean my boiler every week and I take out about 1 small scrub bucket of ashes out of the fire box. Sounds a little silly but it works for me
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I agree with Karl. A coal bed of 2"-3" is ideal. If it gets too deep and I'm around, I'll stir the bed up and make a pile of coals over the nozzle and let that burn down for an hour or two before firing again. I also feel that cleaning weekly is imperitive to get the most efficiency out of the unit. The 20 minutes it takes is time well spent.
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I have found with the g200 thst a coal bed of 2-3 inches is ideal as well.
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Also try adjusting the amount of wood you load to match the demand for the day. Before my 250 I had an indoor gasser with storage that I would batch burn to charge the storage tank, It gave me a good idea of how much wood I need heat my house for the day.
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I've set the air flow controls to specs as per recommendations on this site but if I told you I had a solid grasp of what the restrictor plates in the air-box do...... I'd be lying to you. I understand what the restrictor plate on the intake of the fan DOES, but not really sure the end results and I also don't have a strong grasp of impacts of different rates of air flow directed by the restrictors in the air box or overall flow has on gassing or efficiency of burn. Can someone explain the effects of each of the restrictors in the air-box and the restrictor on the fan?
Don't have any way to measure the moisture content.
The wood certainly could have a higher than optimal moisture content. I know it's drier than any wood I've put into it since I've been using it.
---- Building a wood shed with racks on wheels and THAT has been a priority. Hoping to have racks full (Hopefully 2 seasons) before this coming June.
I would say.... almost half the wood I have stacked is split and still have issues with tenting / doming over the nozzle.
**** Really interested in what the restrictor plates do!!****
Do they changes direction of airflow?
How do they affect gassing and rate of burn??
Also pretty sure the fact that my house is so poorly insulated resulting in very long burns by the 250 prematurely expends the coals necessary to trigger gassing especially over the nozzle.
My experience has been that she is more reliable when I have at least 4-6" of coals (with low ash content) in the bottom of the burn box!!
I'll be VERY INTERESTED to see how she runs with a full compliment of well seasoned wood.
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Others with optimizers can talk to exactly the flow path of the air. My suggestion about the air settings would be to mark or write down what you are currently at so that you have a baseline to compare to and return to if needed. After thst I would open the reaction chamber door so you can observe your nozzle gassing and then expierement with how different settings affect your flame from the nozzle and affect your coal bed in the area of the nozzle.
Your wood may be drier than you have ever used but you stated that you have always struggled with running issues so just being drier than thst probably isn’t the best comparison. From what you described about when your wood was cut and split I see your moisture content being in the 40% area which is very difficult to burn in a gasser without a deep coal bed and small splits.
You didn’t say how big your splits are? Can you describe how you load the stove with wood?
Heating demands do your heat loads vary greatly from user to user. The only way to know how many btu and hour your house is using is to Time how long it takes for the boiler to go from high set temp to low set temp when idling. Best to do this 2-3 times during the day st a given outside temp. Then you can average the time and calculate th btu per hour.
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Ok, I'll give it a go. Others will probably have differing opinions so YMMV, but this is what I have found.
The restrictor plate on the fan acts as kind of a global restrictor to limit the total air introduced into the system. I run mine quite closed down to 1/4" to 3/8". Any more open than that and I struggle with tuning it properly as that fan just creates too much air flow and pressure to gasify consistently.
The top primary plate limits the air flow into the firebox which will determine your rate of primary burn. With dry small splits it's surprising how little air is needed to keep things burning and coaling properly. I am burning very dry wood that has been inside the shed as well as some structured lumber cutoffs, so I have mine closed nearly all the way. It's a round plate covering a larger rectangular hole so the airflow is still there. I found it's very easy to add too much air into the primary firebox and blow the coals out of the nozzle and create a big hole and bridge. With a gassifier you need to be running an oxygen starved environment in the firebox to create the flammable gasses for the secondary chamber. Of course that also requires dry wood or the moisture will create too much steam in the primary firebox and kill the temperatures required for the secondary burn. If you are just blasting the flames into the secondary chamber using the air force of the firebox airflow, you're just running a gasser like a conventional and it won't work correctly. You'll get good gasification for the first bit before the wood starts to burn fully, then it will stop gassifying as all the gasses are being burned in the primary chamber, it will burn a hole above the nozzle and start bridging. I think too much oxygen in the primary chamber burns all of the coals and wood around the nozzle fully as the air is going from the primary to secondary chambers.
The lower plate restricts the secondary airflow into the reaction chamber. I have this set to 5 turns out. This one doesn't seem quite as picky to maintain gasification, but 5 turns for me is plenty to supply enough oxygen for the secondary burn. Any more and it just increases the stack temperature and blows coals up the tubes.
Keep your nozzle clean. Maintain a small coal bed, but not so much coal and ashes that the wood sits too high and creates a potential channel to burn out over the nozzle. Anything more than 2-3" and you're creating the opportunity for the wood to tent over the nozzle and not fall down so it's touching the nozzle and refractory because it's being supported on the sides by the ashes and charcoal. Stir the coals up once a day to bring the charcoal chunks up so they can burn so it doesn't get too deep. I clean the ashes out every week.
Long burns are actually ideal with gassers if they are tuned correctly. If it's gassing well at the beginning of the burn but stops after 10-15 minutes, I suspect the problem is too much air as the wood starts to burn too much in the primary chamber and it wants to burn like a conventional. I have mine tuned well and turned down to a slow enough burn that I am seeing stack temps of only 250 degrees with a good secondary burn and the nozzle glowing cherry red. It can burn this way for hours at a time and maintain gasification. Our natural inclination is to think that more air = hotter, cleaner burn = good. The light came on for me when I realized and accepted the fact that it's really counter-intuitive that you want to starve the fire of air to limit the rate of burn and make it burn cleanly. The nozzle is too small and restrictive to support a full burn in the firebox like you want from a conventional.
What does a typical burn cycle look like?
When does it gasify and when does it not?
What is your differential set to?
How often does it cycle?
It still sounds like your wood might be too high in moisture content. Can you post or PM me some pics what your coal and ash bed looks like as well as the "tenting" to see if that can help with further troubleshooting? Can you send pics of your logs and splits?
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Thats a great explanation
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I find a secondary burn like this, with just about no air, gets me the most efficiency.
https://www.youtube.com/watch?v=IZNOW4raTaQ
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grady is that how your 250 is running again now? same secondary air settings? that video u link said 2014...was that when ur 250 was in service the 1st time?
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Yes that is an old video, it's not running exactly like that now, but not far from it.
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I'm in my 7th season with mine and I must be one of the lucky ones. No matter what I put in it for wood (except for a load of wet wood) it burns it up great. A lot of what I burn is junk that I produce in processing 130-140 cords of wood to sell. It's all partial rotten, knarly knotty pieces - some of which can be pretty darn big, short cutoffs, sweet gum I don't want to split, or just pine that I can't sell. I will add 2 pieces of info here that may or may not help but as already stated a box full of large rounds doesn't do so well. If I have a big piece of gum - one that barely fits in the door and is 24"-30" in length, I need to pack small wood around it. Also, as already stated, my unit seems to do best with 2"-3" of coals.
Even though the wood I put in mine is mostly "uglies" it generally is well seasoned.
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Great Post jreimer!!!
I've done what you suggested and so far it seems to have worked.
Will follow it over the course of the day/week and see how she does!!
The flame into the secondary does not seem as forceful and yet is seems to be a more sustained pure blue flame and the nozzle is cherry red.
Fairly certain that my wood has more than 23% moisture which some have said on her is near ideal!!
Been working on the Wood Shed and rolling rack system. This year I should have 2 years of wood in by June and give it some time to cure. Can't wait to see what she does with that.
Have hesitated to split the stuff I can handle wrangling into the box because I was afraid to create too much surface area to burn thereby burning thru the wood in the primary too fast.
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Pics
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That's great news! Don't be afraid to turn the air down in the primary to keep the wood cooking down to coals instead of burning up in flames in the firebox. Keep us posted with how it performs over the next few days.
I have found that ideally anything over 6-7" diameter should be split once. Anything bigger than that is questionable to fully dry in a year or two. If it isn't dry enough it won't form the nice coal bed you want in a gasser.
The 250 is quite forgiving and very efficient if your wood is dry enough. I have found that you actually can run really small stuff in a 250 due to it's wide range of adjustments. I can burn full loads of small structured lumber cutoffs which was historically considered a no-no in a gasser by turning the primary air WAY down to just a trickle. For bigger stuff you can turn the air up a bit. Now that I understand it, I love the tuneability of the 250.
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Nice pics! That's a big bed of coals! You shouldn't have any trouble burning cleanly with that bed. I would even try to reduce the coal bed somewhat to make sure the nozzle doesn't get too restricted.
I would consider splitting those bigger logs once to get better internal drying and good surface contact with the coal bed. Nice shed and rack system!
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I used to split all my wood to 3-4" splits so I could pack them in there good.
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I have always been concerned about creating too much surface area to burn which would in turn decrease my burn times and efficiency but the more I think about it and after reading the responses to this post, it dawns on me that I am not "BURNING" wood so much as a I am "CHARRING" wood to create the actual fuel which is the by-product of the charring process.
I will be seasoning my wood better and splitting the bigger stuff for next year.
I will also be playing with the airflow settings, with the thought process of facilitating a low oxygen smoldering ( CHARRING )scenario in the PRIMARY with the goal of creating fuel for the SECONDARY and a sufficient base of coals to trigger ignition.
Adjusting the airflow already seems to have made a difference in the tenting or bridging. Has not eliminated it but, I think my primary issue right now is the moisture content of the wood.
Will be very interested to see how she reacts to a more well seasoned fuel source.
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Sounds like you have an excellent handle on the situation.
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Also a reminder to keep ALL of the primary air holes in the firebox clean and clear.
My 250 had been gassing great for the last few weeks, but I was having difficulty sustaining gasification burn in the past few days. I let it burn out and took a look at the primary air supply holes and found a number of them were plugged. I think they plugged up because of idling during the mild temps we had last week. Opened them up and voila! Great gasification again. You wouldn't think it would make that much of a difference because the air volume is about the same, but it does.
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I was having the same issue with mine. I just bought this home and she came with no firewood. I bought a load of oak that had set one season cut in 8' sticks.... Still pretty green. I'm uncertain where the air settings are since the adjustments are froze up (rusted). I adjusted the fan disc to around 1/4" to 3/8" after reading others suggestions. This helped out, but I believe the biggest change came from adjusting my differential to 5 with a set point of 180. After doing this I haven't seen a temp lower then 168 and she starts gassing moment's after the fan starts. Before the fan would run a couple minutes before she'd start gassing. This also cut my wood consumption down. When possible I try to put smaller loads in more frequently, probably 4 to 5 times a day. However when I have filled it and checked it hours later it seems tent less but the important part is I no longer walk up to it not gassing.
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I was having the same issue with mine. I just bought this home and she came with no firewood. I bought a load of oak that had set one season cut in 8' sticks.... Still pretty green. I'm uncertain where the air settings are since the adjustments are froze up (rusted). I adjusted the fan disc to around 1/4" to 3/8" after reading others suggestions. This helped out, but I believe the biggest change came from adjusting my differential to 5 with a set point of 180. After doing this I haven't seen a temp lower then 168 and she starts gassing moment's after the fan starts. Before the fan would run a couple minutes before she'd start gassing. This also cut my wood consumption down. When possible I try to put smaller loads in more frequently, probably 4 to 5 times a day. However when I have filled it and checked it hours later it seems tent less but the important part is I no longer walk up to it not gassing.
Welcome aboard Kevin.
You will have to take the airbox cover of the back of the boiler and clean up the threaded rods that hold the disc, coat them with never seize after you put them back together.