# Down Draft Versus Updraft Gasifiers



## Bricks (Jan 27, 2009)

After reading posts about downdraft gasifiers having a problem with creosote and condensation build up in the main burn chamber for people not haveing storage. I am thinking that since we won`t have storage any time soon if we would not be better off considering up draft gasifiers as these seem to be able to burn the condensation off better when it has been ideling. Since without storage I am sure that it`s going to be a problem.

   Am I maybe right in my thinking or am I all wet.


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## Duetech (Jan 27, 2009)

Welcom to the forum Bricks,
Having creosote in my EKO40 is not a problem. It's there but it's presence is not a problem. I have no build up so to speak because what ever collects to the sides drains down to the fire and eventually burns and that is very efficient. The only build up that tends to be problematic is at the loading door, the loading door shelf and at the bypass damper and generally that is a "seconds fix" for either location but only every week or two and less if the wood is in the ideal moisture range. Not all of my wood is down to "ideal" moisture content and that alone could be problematic but it is not because you learn the characteristics of your boiler. Most of the complaints or concerns I have come across are from people who have just started using their boiler and want to know if they should be concerned or not. That is not to say that all gasifying boilers are created equal as there is one brand that does seem to have a couple problem areas. OWB's in general have the same collection and drain and burn cycle and nobody is taking out buckets of creosote. That would certainly be a "Green" issued to catch the eyes and ears of the "Ecological Front". My boiler is in it's third season without storage and I use my boiler for domestic hot water even during the summer and has had a fire in it every day minus about 15. Summer time idling without storage would be/is the worst time to have creosote problems and like I said."It's not a problem". That said...

...Each gasifier has it's characteristics and I am not trying to dissuade you from any particular type or model or design. I will not be living with your choices. I am trying to help you make an informed decision though. Try PM-ing people who have a large number of posts in the forum and who display their type of boiler and ask them if they have problems with creosote or not. Testimonials are some of the best "inside track" information you will get.


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## Nofossil (Jan 27, 2009)

People who are new to gasifiers sometimes are sometimes concerned about the creosote deposits that form in the upper chamber. They are not a problem and do not need to be removed. I have never seen any condensation at all, even the year that I ran with no storage. I think condensation is a problem only if you have wood with a high moisture content and idle a lot.

I don't have hard data on this, but I believe all the gasifiers that have been independently tested and achieved efficiencies above 85% are downdraft type. The advantage of downdraft is that the flammable gases are superheated by passing through the coal bed before hitting secondary combustion.


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## stee6043 (Jan 27, 2009)

The way I see it the creosote in my upper chamber is a GOOD thing.  I'm hoping someday that it will combust and provide all kinds of extra btu's for the 10 minutes it burns!

Not likely.  The black stuff in the upper chamber is honestly the last thing I think about unless I end up with a bunch on my shirt sleeve after building a new fire...


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## MaineMike100 (Jan 27, 2009)

I am also considering a downdraft boiler, most likely either tarm or eko.  What is everyone's experience with repair costs?  Are there any high priced parts such as refractory bricks/ nozzles, etc. which need replacement on a yearly schedule?


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## MaineMike100 (Jan 28, 2009)

Bump...  Any real world experience with repair costs?


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## Nofossil (Jan 28, 2009)

MaineMike100 said:
			
		

> Bump...  Any real world experience with repair costs?



I've had mine for 3 1/2 seasons and have no experience with repair costs yet. It's a pretty simple beast. I suspect that the loose refractory pieces in the secondary chamber don't last forever, but they should be cheap to replace.


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## MaineMike100 (Jan 28, 2009)

Thanks Nofossil.  Just wanted to make sure I'm not getting in over my head with something that will be a burden to maintain.  I know the right answer is to spend the extra now for a gassifier, but I guess my yankee upbringing makes it hard to part with the money.


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## Piker (Jan 28, 2009)

I tend to think that the thick runny creosote is less an enemy than ash left to sit in a boiler over the off season.  Creosote, ash and soot are all acidic, but pose very little corrosion problems until moisture is introduced.  A loose pile of ash in an unused boiler over the summer will likely draw damp and begin the process of corrosion to the boiler jacket.  The thick runny stuff gets hard when it's cold, and there really shouldn't be any moisture to speak of that can actually get to the steel that is behind it.  

As far as I know, creosote is not an issue in the upper chamber... it does exist however.  It will reduce thermal transfer, but the idea of a gasifier isn't to get a bunch of heat off of the inneficient combustion of the upper chamber anyways, so maybe it would improve overall efficiency by forcing the boiler to gasify more... though overall boiler output might be slightly less.  That is just a theory of mine... I don't actually have any scientific data to back that up.  Do you have a take on that Nofossil?

cheers.


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## markpee (Jan 28, 2009)

Cave2k said:
			
		

> and I use my boiler for domestic hot water even during the summer



Caveman - I assume you get a lot of idling in the summer - how long does a load of wood last in the summer?  Weeks?


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## cguida (Jan 29, 2009)

Is there such a thing as an up-draft gasifier, aside from the Seton-type boilers?


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## Medman (Jan 29, 2009)

The above is quite correct.  in my EKO 25, the creosote builds up in the upper chamber but is not a problem.  The only buildup of any sort in the stack is fine flyash - about half a gallon pail's worth after two months burning almost non-stop.  This built up in the bottom of the Tee I installed on the back of the EKO.  I just dropped the bottom plug off and emptied it out. The rest of the pipe and the rain cap have no buildup at all.
As for burning off the creosote, this week my wife loaded the boiler during the day but forgot to close the bypass damper.  When I got home from work the boiler was at 200*, the stack temps were at 750* (first time I have seen it above 400*) and the upper chamber was clean!  I think in the spring I will do a more controlled burn in the upper chamber to clean it out before the summer season.  If I get the storage installed I will be burning in the summer too, for DHW.


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## ISeeDeadBTUs (Jan 29, 2009)

Smee said:
			
		

> Is there such a thing as an up-draft gasifier, aside from the Seton-type boilers?



Funny, I was just mulling this over the other day.

First, I like to stay away from the whole term "gassifier". I think it can be misleading.

But the exhaust path in the GW (I assume this is true for all Seton spin-offs) goes UP from the fire box (primary combustion chamber) then goes DOWN, where the bulk of the heat exchange takes place. This accounts for the 'smoke out the feed door' issues, IMO.

What I don't know is, Is there any 'secondary air' added? If there is, it is natural, not fan driven. But thankfully I've not had my GW apart yet to know how/where any secondary air would come in. The only openings seen are the 4 air inlets at the back of the unit, and these appear to exclusively feed the primary combustion chamber.



			
				Medman said:
			
		

> When I got home from work the boiler was at 200*, the stack temps were at 750* (first time I have seen it above 400*) and the upper chamber was clean!  I think in the spring I will do a more controlled burn in the upper chamber to clean it out before the summer season.



The GW doesn't build up creosote on the primary combustion chamber, but it DOES on the heat exchange tubes. I can tell you this . . . when the power went down and the green beast cooked, the tubes were SPOTLESS afterwards :bug: 

Jimbo


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