Creosote

[Welderman85]

I'm new to burning and trying to learn. Today my wife was asking me questions about running the insert. Her #1 question was what causes creosote. And I couldn't really give a good answer on all the things that cause it. So what are the things that cause it ? Thank you

 

[sweedish]

#1. Burning wood over 20-25% moisture content.
#2.See above.

 

[begreen]

Creosote is the accumulation of condensate from wood gases on the flue interior surfaces. Condensation occurs when the flue gases get below about 250º.

 

[weatherguy]

Burn wood below 20% properly and you wont have to worry about creosote, also clean your flue every year.

 

[peakbagger]

Burn wood perfectly (hot and dry) and the only thing that goes up the stack is carbon dioxide, oxygen, water vapor and some gases like nitrogen and argon that dont participate in the burn. If the wood doesnt burn hot enough in the firebox there are various partially burned gases that make it up the stack. These partially burnt gases are all a vapor when they leave the firebox, some will condense back into liquid when cooled, some will not. The stack is cooler so some of the unburnt gases will condense on the stack walls and some will not. The big non condensable unburnt gas is carbon monoxide, it goes into the air out of the stack , while the condensable stuff best called "tar" gets mixed in with the water vapor that is going out the stack and condenses on the walls of the stack. The tricky part is the stack is hotter on the bottom than on the top. If water vapor with tar condenses at top of the stack, gravity is going to pull the liquid water down the walls of the stack towards the bottom of the stack. The tar has a higher boiling point than the water so as the liquid water with tar drops down the stack heats up and the water turns back to vapor the tar remains. This slowly "bakes" the tar from a brown liquid to a sticky liquid eventually into glassy hard solid.

Both the carbon monoxide and the creosote have fuel value. Some folks have built wood gasifiers to produce carbon monoxide and they can run and engine on it. There is a commercial process that intentionally makes a refined form of creosote from wood, it ends up resembling #4 fuel oil and is used in a few spots to replace heating oil in institutional boilers. That means the carbon monoxide and creosote are wasted energy from the wood which isnt heating your house.

The creosote will still burn once its heated up enough to turn back into a vapor. Usually this happens when the stove is run hot after several weeks of idling along building up creosote. When it lights off in the stack it burns hot which melts more creosote into a vapor which burns and gives off more heat which sets off a very hot fire in the stack and will look like big blowtorch at the end of the stack. It will burn until runs out of burnable creosote or the fire department puts it out. It can crack chimney tiles and permanently damage liners. Its a very scary event. Do yourself a favor and search You Tube for some good videos of chimney fires especially the ones at night where the flames torching out the end of the stack are quite apparent.

 

[jlinz]

What if I have dry GREN bricks (condensed hardwood) that I'm not bringing up to a hot enough temp consistently? So, it is very dry, but my stove is only reading near 300 when burning? I've done this maybe for 6 or so fires since I'm still learning to really let things rip.

 

[kennyp2339]

So, it is very dry, but my stove is only reading near 300 when burning?

Dryness helps facilitate hot fires, a hot fire will do better as the fuel and smoke is burnt cleaner, also the by product is a hotter flue which mean less of a chance of smoke condensating and causing significant build up in the chimney, shoot for a 500 - 700deg stove top.

 

[jlinz]

Dryness helps facilitate hot fires, a hot fire will do better as the fuel and smoke is burnt cleaner, also the by product is a hotter flue which mean less of a chance of smoke condensating and causing significant build up in the chimney, shoot for a 500 - 700deg stove top.

I am trying. I suppose the way there will be to start with more bricks and then close the damper some as the fire gets to a place where it is going strong. Still figuring it out, haha.