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Maxim burn chamber full of tar after just 4 days

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by danjayh, Oct 18, 2012.

  1. danjayh

    danjayh New Member

    Joined:
    Aug 23, 2012
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    I fired up my Maxim last Sunday when it was cold here, at which time the burn chamber was quite clean (I'd scraped it down to the metal in most places). After four days, it's a tarry mess, as shown in the attached images. I'm just wondering if anybody else has had this experience while burning pellets, and if it's just "normal". If not, I have three theories, and I'm curious if anyone has any input:

    - My pellets may suck. I'm currently burning Michigan Wood Fuels pellets that I got for $3.50/bag at Home Depo, but they have terrible reviews. Can crappy pellets cause this tar?

    - My air/feed rates may be set wrong

    - It's idling too much. After I filled it, the temperature came up a ton, so it has been idling a great majority of the time. Even so, I'm still surprised at the huge extent of the tar buildup. Can this possibly be normal (see pics)?

    Thanks!

    Attached Files:

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  2. heaterman

    heaterman Minister of Fire

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    Oct 16, 2007
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    Loc:
    Falmouth, Michigan

    I don't know where you are located but the 2 brands I have found to be the best are Michigan Wood Pellet out of Grayling Michigan and Indiana Softwood Pellet which are as the name says made entirely of what is considered softwood type timber.
    Michigan Wood Pellet (not to be confused with Michigan Wood Pellet LLC from Holland Michigan) are made from the by product of a high density particle board factory up in Grayling which supplies interior truck and car panels for one of the Big 3. Being that they are made from wood which has already been processed they contain no bark or dirt and from what I see leave about 2 oz. of ash per 100 pounds of pellets. Very good and very consistent quality.

    The Indiana softwood pellets may actually burn a little cleaner bu they are bulkier due to the lighter weight nature of the wood being used. A full pallet of them standing alongside a pallet of the Michigan Wood product is about 8" taller for the same weight.

    My brothers in the hardware store sell both brands after trying dang near everything available on the market and have found these two the best. The Michigan Wood Pellet sells for $195 a ton right now and the Indiana Softwood product is a little higher..

    Now.........that being said. No matter what brand you buy. make absolutely sure that the pellets are kept indoors and not stacked up out in the parking lot in back of the store selling them. Those bags have small air holes in them to allow the pellets to "breathe" and not turn to moldy dust. I just shake my head when I see 40 or 50 pallets of them stacked up outside a store sitting there in the rain or snow in all kinds of weather. How those pellets are handled at the store selling them is very important. I don't care how cheap they are, if they are stored outdoors they are not worth any amount of money. Buy your pellets from someone/someplace that has actually done a little research on the product rather than a joint that just pushes stuff out the door with a happy Seeya!
  3. danjayh

    danjayh New Member

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    So do you think this amount of tar is mostly due to the pellets and not the idle time, then? I was worried that it was due to the idle time, which would pretty much prevent me from being able to use the boiler during shoulder season ... but if it's most likely the pellets, I'll just switch out and keep going.
  4. harttj

    harttj Member

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    Ohio
    How much air? I don't think it is from idling. The burn pot looks good. Is this tar or just metal looking black?

    Edit: I've never seen tar like that. Either pellets or not enough air.
  5. heaterman

    heaterman Minister of Fire

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    Does the boiler have the capability to have the firing rate turned down? Less air and less fuel? That would give you less idle time in shoulder seasons.
  6. heaterman

    heaterman Minister of Fire

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    It could be pellets. The easiest way to tell would be to buy a few bags of a different brand and see what they do. If you get the same result in similar weather conditions then you would know there is an air/fuel ratio problem.
  7. danjayh

    danjayh New Member

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    I have the pellet feed rates all turned down to the minimum. In idle, I have the air on the second to lowest. In medium and high I have the air set to about 30-50%.

    EDIT: Also, it really is tar. I scratched at it with my poker and it's gooey and slimy (at least while the boiler is hot ... I'm guessing that when I let the fire go out so that I can clean it it gets hard, and difficult to remove).
  8. danjayh

    danjayh New Member

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    I have the fuel turned all the way down for all three modes (idle, medium, and high). I adjusted the air by peaking in the burn pot occasionally to see how big of a pile of pellets there was ... I have it adjusted so that it doesn't burn all the way back to the auger, but also so that a big pile doesn't build up.
  9. ozzie88

    ozzie88 Member

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    Hello, have you ever took a peek out the chimney while it running and then try different adj. on air and see the smoke change? I found that this is good way to tell if runnig rich or lean,it looks like it running rich, to much fuel and less air?
  10. danjayh

    danjayh New Member

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    So I have the fuel turned all the way down for idle ... is there any reason why I'd want it to be higher than that as long as the fire doesn't go out? I adjusted the air rates by peaking in the firebox to see how much unburned fuel was building up ... at my current air settings (pellet feeds all all the way down, air roughly in the middle for non-idle modes), never more than the back 1/3 of the burn pot is full of fuel.

    In idle (which is how it spent most of the time during which this tar built up, due to weather fluctuations), I have the air set to the second to lowest setting, and the fuel set all the way low. For the Maxim, though, the idle air adjustment just configures how long the fan stays on for when it does run - in idle it always spends most of the time completely shut off.
  11. ozzie88

    ozzie88 Member

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    maine
    Maybe, I think this may be building not so much when idel but when running? It still could be running rich while when you look at fire itself may look ok,but comeing out chimney is where excess fuel[smoke] will show up,this will collect like the tar you see.[still could try different pellets still] but I think it in adj. of fuel or both
  12. Mike49024

    Mike49024 Member

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    Loc:
    SW Michigan
    Any updates?

    I'm having a very similar problem that I just noticed yesterday. Haven't done much research, but I thought I'd come on here to see if there was any info. I suspect its crap pellets because I too am burning Michigan wood pellets LLC for the first time, and have never had the problem in the past.
  13. danjayh

    danjayh New Member

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    I'm still not sure exactly what caused it, but my money is on sitting idle for too long. The 3 day span in which that happened had highs in the 60's to low 70s, and lows in th 50s to high 40s. At those temperatures, my house wasn't giving the boiler any load at all, so aside from the few times it turned on every day to keep the water heater up to temp, it sat idle for almost 2 days. In retrospect, I probably should have just shut it down.

    That being said, I think *maybe* pellets played a role. Where did you get your MI wood fuels pellets? I later got another batch at Menards (at $158/ton, I just couldn't say 'no'), and they are a different color and make the fluffy type creosote that's easy to clean (although they make a lot of it, and a lot of ash). The batch that I had all the problems with came from Home Despot, if memory serves, and had been stored outdoors in the 'Garden Center'.

    I also later had a very mild 'tar' problem with Pro Pellets when it was unseasonably warm one day, and they're supposed to be top-notch.

    The other thing that I did that dramatically helped my problem was to adjust the boiler settings on the Maxim so that 'high' mode doesn't kick in nearly as quickly. In the factory default configuration, it goes to 'normal' mode when the water temp gets to be two degrees down, and 'high' when it's been running for at least 10 minutes and gets to be four degrees down. What this meant for my boiler is that it'd kick into 'high' almost every time the furnace fan came on, quickly recover, and then sit idle. I modified the settings so that it went to 'normal' when two degrees down, and doesn't go to 'high' unless it's been running for at least ten minutes and is eight degrees below the setpoint (which I keep at 180). With this configuration, my boiler spends the majority of its time running in 'normal' mode if it's below ~30 out, typically at a temperature between 74 and 79, and I've never seen it drop below ~170 or so. This results in a much cleaner burn and less build up, and as a bonus, since the air velocity through the heat exchanger is lower during the heating cycles (due to not running in 'high' mode normally), it should be more efficient as well.

    It's supposed to be in the high 50's here friday/saturday, and I'm planning on shutting mine down for a few days to avoid new tar buildup (the old tar hardened into stage 3 creosote, and I still haven't been able to fully remove it).
  14. SmokeEater

    SmokeEater Feeling the Heat

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    My first thoughts are not to find fault with the pellets. My pellet boiler has not ever had the smallest deposit of tar or creosote within it. It often idles and in fact it idled long enough today that it's sensors shut the boiler down due to the very warm day we had. I haven't touched the controls, but know that it will resume fire tonight when things cool off. Looking into the firebox shows only white to gray fly ash. The ash in the pan is uniform in color throughout indicating that even during idle burns, no creosote is formed. I would look at the combustion fan and its controls. If that proves to be normal, then you might check your chimney's draft. The buildup of tar is definitely related to the amount of air supplied to the fire. If the auger was feeding too fast, you would find unburned pellets in the ash pan. It's draft or fan, or both.
  15. danjayh

    danjayh New Member

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    HI SmokeEater! Thanks for the reply. A couple of questions about your harman - when it idles, does it continue to feed wood and give the occasional puff of air to keep the fire going? Also, not counting your buffer tank, how much water does the boiler itself hold? The Maxims do use pellets/air to idle, because they use a lot of propane when they need to restart. If it was an option, I'd still just have it shut down anyway, but it's not. The maxim has three burn modes - "high", "normal", and "low", each of which has an adjustable feed & air setting. By default, they click into "high" when the water temp is 4 degrees down, and quickly recover to the setpoint, leading to a lot of idling for any installation where there isn't a lot of load (the newer models have fixed this). What I did do that helped quite a bit was modify some of the 'hidden control variables to make my older maxim behave more like a new one - now it doesn't go to high mode until it's 8 degrees down from the setpoint, giving it 6 degree range to run in 'normal' mode (it doesn't come off idle until two degrees down). With the settings configured like that, my boiler spends a large majority of its time in 'normal' (except when the thermostat set back from 73 to 67 in the morning and at night), and I haven't seen tar since.

    That being said, I do still get fluffy, 'loose' creosote adhering to the walls of my boiler that'll probably require cleaning every ~2-4 weeks. I need to check my return temps, but since the boiler itself never gets below ~170 or so (the sensor is pretty far away from the returns in the 90 gallon tank) and the creosote is pretty evenly distributed (and not concentrated around the water return location), I'm thinking that it might just be a fact of life.
  16. SmokeEater

    SmokeEater Feeling the Heat

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    danjayh, when the Harman goes to idle I think a timer starts, because after a time, if idle continues, the feed auger stops feeding and the fire dies to cold. When idling, the combustion fan has variable speeds and the Harman slows the fan, but the draft doesn't stop and cycle. At this burn, I think it burns about 1.0 pounds per hour of pellets. The high temp and low temp of the 50 gallons of water can be set between a range of about 130 and 195 degrees. If you set the high temp at 190 and the low at 140, the Harman will reach the high set point and then if there is no load, it will go into idle and keep the temp at 195 until it times out (hours). Then it will not restart until the water temp cools to the min set point, here at 140. No creosote.

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