Creosote?

[doctorb]

I know what it is when I see it (like pass interference in football), but what is it really?  What does it consist of?  Is it affected by the "sap" of the wood, hardness or softness, combustion temperature and heat production of different species of wood?  Finally, how can you prevent or minimize its production?  It certainly is combustible, once the right temp is reached!  Your thoughts.

[ely]

seasoned firewood will produce less of the buildup in chimneys, my buddy usses green wood for smoking meat and his smoker runs that stuff out of it very bad.

[Tom]

It's the condensed, unburned volatile fuels from a slow (cool) fire.

We get creosote from burning fat-lighter (pitch pine) in the south when we choke down a fire made with it and cause it to produce volumes of black smoke.  It is also caused when the wood you are burning is not seasoned and/or is wet.  The fire doesn't get hot enough to burn all of the volatiles that are being released.  They go up the chimney and condense on the walls of the flue and chimney, just waiting for the day that the fire is big enough to ingnite them.

If, one day, you make a bigger fire and the creosote/condensate ignites,  there will be one of the hottest fires in that chimney that you could ever imagine.  Steel stove pipes will glow cherry red and approach white.  The insides of brick chimneys will melt and the mortar will burn out of the joints.  There will usually be a rushing/roaring noise, as if a jet engine is running in your fireplace. It is an eye opening experience and very dangerous.

[doctorb]

OK - then please explain this.

When I open my outdoor stove, especially when the fire has been idling for a while, you can see creosote dots overe the surface of the exposed wood.  Is this from it dripping off the ceiling of the firebox?  Other times, after the fire has been buring for a while, a thin layer may be left on the walls, but I don't see any of this on the wood.  Must be related to temp, I assume.  At what temp does it ignite?

[Tom]

Doc,
I can't speak for your stove.  My experience has been with fire places and small wood stoves.  But, you might get a better idea of what you are up against by googling Chimney Fire instead of creosote.

[doctorb]

Tom-

Actually I don't think I have a problem.  More curious than enything.  This stuff burns off with a hot fire.  Now that the weather's colder, the stove fires up a little more often and that seems to do the job.

I have experienced one chimney fire in my life.  My dad was given a crate of grapefruit for Christmas once, and we threw the thin wooden sides of the crate (after removal of the wire) into the fireplace.  The entire fireplace went white hot, the flue started to roar, and my dad got up on the roof watering down the sparks that were flying out of the chimney.  Luckily, it burned itself out without damage or destruction.

I may google around trying to find a relationship between moisture content of wood, species of treee, and creosote production.  I think that this will be hard to quantify, as each fire, each flue, etc., etc. is different.

[Tom]

Yeah, you are probably right.  Some chimneys go for years without even being cleaned and some light up after just a short while.  I've only seen one bad one myself.  It was in metal pipe from a wood stove.  A friend of mine and I were cold and built a fire.  We didn't realize how hot it had become until the chimney began to get almost transparent. 

It scared us to death. The chimney came out of the stove and ran horizontal about 10 feet before it went through the wall.  The whole thing was cherry red and we were afraid that the wires that it was hung with were going to burn through.  luckily, it burned out before his Grandmother found out.

If we didn't do anything else, we made it safe for them to use the stove awhile longer.  :D

He and I would drive around the dirt roads in his old 30 something ford pouring gasoline into the carburator from a coke bottle because the fuel pump was broken too.

Ahhh-h-h-h-  youth. 

[beenthere]

OK - then please explain this.

........................, you can see creosote dots over the surface of the exposed wood.  Is this from it dripping off the ceiling of the firebox?  ........

I've seen similar and it was moisture and residue bubbling out of the hot wood.  Might be what you are seeing.

The inside of my boiler has creosote on the walls where they are backed up by a water jacket that keeps them cool. But in 35 years, I've never removed any of that creosote and it hasn't become any thicker over time. So I presume it burns off. I'd estimate it is 1/4-3/8" thick at most. The ends where there is no water jacket just get some soot-like residue. 
And I've experienced a few chimney fires too. So far, no damage and I try to keep the chimney clean. And a few times a winter I try to force a chimney fire if I can't get on the roof due to snow to drop a brush down. I want it to happen when I am here.

[John Mc]

I'm far from a wood boiler guru (nor do I play one on TV, and I didn't even stay at a Holiday Inn Express last night, but I have done a good bit of reading on this, and have had several in-depth discussions with a friend who designed some wood boiler systems and knows a lot about wood combustion).

The best ways to avoid creosote formation is to burn properly dried wood in a hot fire with the appropriate amount of air. Green,wet or only partially dry wood will tend to form more creosote when burned. IF you can get the fire hot enough, you can reduce this. Choking off the air and smoldering the fire also increases creosote formation dramatically. Both of these conditions also significantly reduce the efficiency of the burn.

Some systems (particularly some large commercial wood chip boilers) are designed to operate on fuels with higher moisture content -- their combustion chamber and other systems have been designed around this. Most home systems have not. Just because they can burn wet or rotten wood, does not mean they will do so cleanly and efficiently.

[hockeyguy]

I've noticed the same creosote buildup you guys mentioned dripping from the ceiling of my e classic. I also have a smooth tar like layer all around the firebox as well as build up in the corners.

My question has less to do with fire danger and more to do with possible damage (corrosion) due to creosote. Even with regular cleaning, does creosote buildup eventually cause corrosion?

Even with well seasoned wood, the e classic (and I believe many other owb's) have long idle times without air being injected into the firebox while the fire smolders thus causing creosote to form. Seems to me it's gonna happen no matter what to some extent. Am I wrong?

Thanks to all for the great info.

[beenthere]

hockeyguy
You are not wrong. Anytime a woodburner shuts off the air supply to stop the burn, there will be smoldering and creosote form. It is the nature of the beast. How to best deal with the creosote is the question.
How to adjust the fuel supply and burn settings and using up the hot water so the burn can continue will help control the creosote.

Can't turn wood on and off like a gas burner. When it is shut down, creosote forms. Having enough hot coals to fire up that wood again when heat is called for, remains a problem to deal with. Personaly, I think one culprit here is the large water storage capacity of the OWB. But there are good arguments for having it.

I don't think creosote will corrode the steel.

[doctorb]

I think I see more creosote this year than last.  Maybe my wood is not as dry.  Maybe it hasn't been cold enough for the fire to restart itself at more frequent intervals.  I lit my stove in mid-December last year, (November 1 this year) and it was nasty cold outside.  So I have never really seen the furnace under a "fall" climate versus a winter climate.  I would think that extended idle times would only increase creosote formation.

As far as "boiling residue" out of the wood, I never see moisture seeping or boiling out of the logs when I look inside at the fire.  Inside of the firebox looks more like there was a "mini tar explosion" in the chamber and the drops landed everywhere.  Crude and uneducated observation at best!!

I do know this, when we took down my stack at the end of the burning season last spring to do a little roof work on my shed, the e-2300 stack was a clean as a whistle - no creosote buildup at all.

I will remeasure my wood moisture content (last time this season) and post on the seasoning firewood thread.

CB does not want your to burn the furnace with the bypass door open for fear, I assume, of a "chimney fire"in the stack.  Does anyone use the creosote retardent?  I have never used it becasue, except for some sticking of the bypass door, creosote buildup has not caused me a problem.

[Magicman]

The moisture in your wood is water.  That may affect how fast the wood burns and how much air that you need.  Creosote is a product of incomplete combustion, whatever the reason.

To stop or to control a chimney fire, shut off or regulate the air supply.  You can't do that with an open fireplace, but you can with a heater or fireplace insert.  I have had many over the years.  The reason; here in the South our days can really heat up and we have to choke off the insert.  That causes a massive amount of creosote buildup.  Every couple of years, yup, it's going to catch up.

[PineNut]

I burn whatever wood I have available in my OWB. Since I cut a lot of pine, it is frequently pine slabs. Yes, it does make a lot of creosote when I have a smoldering fire. As a result, I usually burn mine out about twice a week. Having just a short stack (3 ft), it is no big deal.

[JJ]

I think the Creosote helps get the fire going, after long idle.
Once the blower starts, it (fire) spreds and flashes over quickly.

pretty disgusting stuff however!  I am daily scraping gobs of the gue off the shelf, where the fire bricks were in my e-2300.

          JJ

[Autocar]

I laughed to myself when I opened up this thread,I though you were talking about the creosote in power poles or rail road ties  :D I haven't had any creosote problem sence I went to this Green Wood Boiler. The inside has a white dust and the flame is different then any color Ive ever seen. But it dose use alot more wood then my old warm morning.

[northwoods1]

I laughed to myself when I opened up this thread,I though you were talking about the creosote in power poles or rail road ties  :D I haven't had any creosote problem sence I went to this Green Wood Boiler. The inside has a white dust and the flame is different then any color Ive ever seen. But it dose use alot more wood then my old warm morning.

Yah that is what I was thinking too :D I still have a 5gl pale of that stuff wondering what to do with it. This thread however got me to thinking and this might be a stupid question but has anyone ever heard of an outdoor wood burner getting a chimney fire and burning up because of excess creosote?

[Reddog]

This thread however got me to thinking and this might be a stupid question but has anyone ever heard of an outdoor wood burner getting a chimney fire and burning up because of excess creosote?

No but they start grass fires a lot.

[sawguy21]

My buddy's dad and grand dad installed highway guard rails in the early 60's. They brought the ends of the creosoted posts home and used them for firewood. The blocks were dirty to handle and stunk.
Of course the night sky would light up periodically, fortunately neither set the house afire.

[John Mc]

I laughed to myself when I opened up this thread,I though you were talking about the creosote in power poles or rail road ties  :D I haven't had any creosote problem sence I went to this Green Wood Boiler. The inside has a white dust and the flame is different then any color Ive ever seen. But it dose use a lot more wood then my old warm morning.

Not surprising that it uses more wood, since you waste up to about 40% of the BTUs burning green wood vs dry. Some of this is from heating up and then vaporizing the water in the wood. Some additional BTUs are wasted by not burning all of the gasses which come off the wood, unless you manage to get a hot enough fire to ignite them (tougher to do with wet wood, but possible).

[gyro jr]

I have found that the easiest way to clean the burn chamber of my e classic is throwing in some very green wood and letting it sit idle. The creosote is much easier to scrape off the walls, corners, bypass area. I usually do this once a month, to keep the build-up to a minimum. Just watch the stuff as it drops into the coal bed. Smoke and then some; must work pretty fast.

[doctorb]

gyro jr -

I am not sure I understand.  You throw green wood on a hot coal bed, turn off the fans, and let it burn on its own?  Door open, bypass open?  Why would green wood burn off more creosote than seasoned oak?  I am intrigued by your suggestion.

Doctorb

[gyro jr]

doctorb,
I found that cleaning the firebox was a chore that I did not fancy at the end of the heating season. The creosote buildup was heavy and not easily removed without a "jack hammer." This is the point, make things easier. On the warmer days when the boiler is sitting on idle mode. No call for heat. I throw 2 damp/green 12x24 logs on top of a good coal bed and let it go for the day. The steam created from drying out this wood does a great job loosening up all that gunk. Just grab a paint scraper and it comes off easily. Once a month is what I do and works great. I burn 15 chord/year.