Creosote question

[WV Sawmiller]

   Okay, it is well established that burning green wood causes creosote to build up in the chimney. My question is where does the creosote go in dry wood? When wood dries as I understand the only thing that would evaporate out would be moisture.  Looks to me like dry and green would in theory would both have the same creosote content. Does dry wood burn that much hotter so that it burns up more of the creosote during combustion or what?

   Just another one of those wild ideas that popped into my mind while bringing firewood in that afternoon.

[Ljohnsaw]

I always hear that creosote builds up is from too cold of a fire.  If the wood is green, it spends too much heat energy drying out the wood so it is relatively cold.  This cooler smoke can then condensate inside the flue (since the flue didn't get cooking hot!).  They make those temp gauges to stick on the metal flues that tell you if you are creating or burning off creosote.

But, an interesting question!

[toomanykids]

I'm new to the wood burning stove game but I've been reading a lot on it and yes you're right, green wood means cooler fires, which means more smoke which is part tar escaping up the chimney which condenses into creosote. a good hot fire means those gasses burn up inside your stove, more heat and less creosote, so bright flames good, smoke bad in the war against creosote

[coxy]

I'm not convinced that is right we always burnt green wood in our airtight wonder wood stoves they was burnt wide open little to no creosote when I lived in my other place I had more trouble burning seasoned wood with the creosote build up from the stove not burning hot (as in the damper was shut down all the time as was to hot in the house) yes dry wood is more heat but the stove never gets a chance to really burn hot mostly just smolders  just thought I would put my 5cents in on this post 

[lopet]

Yeah, I had some trouble too with last year's mild temperatures. A lot of creosote build up in my owb, spend two hours chipping away and cleaning up last spring  to  have it ready for the next season. And then fired it up end of October and  run fine at the beginning until November came. Then we had some  pretty mild temperatures with some smoldering   fires, which caused creosote to build up in the elbow before it gets to the chimney and eventually clogged it. After cleaning it out, I finally cranked up the thermostat to 180 when it shuts the damper, and all that crap fell right of the walls. Should have done that a long time ago.     Now I am a happy camper .

Never thought of burning green wood , because me grandpa taught me different, but a hot fire sure makes a difference.  :D

[Don P]

It is unburnt tars and whatever condensing in a cool flue, wet wood is more prone to a cool fire but if you choke down a fire and the stack goes below about 190 stuff is going to condense inside the stack rather than being either burned in an oxygen rich hot fire or escaping the top of the flue as hot gas. Since owb's fire up a large quantity of wood and then shut down and smolder, they also tend to create lots of creosote.

I've wondered, if we dissolve this creosote in a solvent does it have similar preservative properties as the old coal tar creosote preservatives.

[Rural]

I read somewhere that you can make creosote by 'cooking' green wood in a closed container, not something we want to happen in our woodstove! Airtight stoves that smolder all day certainly would seem to fit that idea, I always let the stove roar and get the chimney good & hot when relogging first thing in the morning and have never had a creosote problem, checking the pipe before the season starts I have not seen any build up in my 20' of chimney.

[John Mc]

Some of the products of combustion of wood are gasses. Some of these gasses are themselves combustible, but they will not combust unless they get hot enough. When they don't combust, the gasses can condense out, forming creosote on the flue walls.

A cold fire will produce more creosote than a hot one. There are (at least) two ways of getting a cold fire: (1) burning green wood tends to cool off the fire, causing more creosote production or (2) "smoldering" the fire by starving it for air.

It is possible to burn green wood hot enough to ignite the gasses, minimizing the creosote production. (Depending on your set-up, you may have to work at it to get it this hot, however.) It's possible to get creosote from well-seasoned wood by choking off the air to the fire. Some wood burning appliances are designed to burn green wood. One type of design uses a secondary combustion chamber to burn the gasses.

Catalytic stoves tend to be able to handle a cooler fire without producing more creosote. Once it has heated up enough to ignite the gasses, the catalyst can keep them burning even if things cool down a bit.

If you are having creosote problems from burning properly seasoned wood, it's likely you are not allowing enough air in to achieve complete combustion. If allowing in appropriate air produces so much heat you are driven out of the room, your heating appliance is likely oversized for the conditions & heat load.

Wood combustion generally doesn't like to be "turned down" very much (and modern EPA certified stoves generally are designed to prevent them from being turned down this much). If you are being driven out of the house, burn fires less frequently, or get a smaller woodstove. A common way of addressing this problem for OWBs is to add external water storage. This allows you to run the OWB at full blast to heat up the water, then shut off, using that water for your heat source until it's cool enough to need another blast of heat.