Burning pallet lumber (Lots of Smoke)

[E Yoder]

Yeah, gray smoke is a cool steamy slow burn, black/yellow usually is a rich and hot burn.
Those sticks would probably burn slower and cleaner if they weren't so dry. They ignite too easily.

[Peter Drouin]

Did you ask someone if the wood is treated with something?

[coxy]

mine will do the same thing if i burn boards or pallet wood don't know why but it will stop after it gets up to temp and wont do it again till you refill it i thought it maybe burning the creosote off the in side of the boiler like the boards are dryer  making more heat or there is more air space letting the flames hit more of the inside of the fire box burning the creosote off  hope you get the idea of what I'm talking about 

[Don P]

It's what E Yoder is saying. You are heating the wood enough to make a large amount of wood gas and have insufficient oxygen to burn it so that rich unburned gas mixture is spewing from the tailpipe. If you hold a propane torch up there it may well flare. Later in the burn you are basically burning charcoal. Basically you are gasifying without provision for taking advantage of it. That is methane and unburned hydrocarbons spewing from the stack. With dry wood like that a catalytic converter on top of the stack with air intake would provide ignition temps and oxygen to clean it up. You wouldn't get any advantage from the heat produced but it would clean it up. Slide that out of the way when you burn wet wood, which is another problem.

[jason.weir]

WOW! I have burned green softwood and hardwood,cut it down and 15 minutes later it's in the OWB. Rotten wood that must would not even pick up. I have never seen black smoke like that. Yes gray,but not black like that. I wonder what's on those boards?

My experience as well - never seen black smoke out of my OWB unless I used something to "help" get things going...

[Gary_C]

You should also check your exhaust system to make sure there is no buildup or obstruction. 

[TKehl]

I'm with Don P on this.  Hot box, lots of surface area, but a smallish fire.  Perfect for pyrolysis and pyrolysis is great for producing wood gas.  

[Crhall]

I completely understand whats going on. I knew from day one seeing all the dark smoke is unburnt fuel. Theres no question about that. My whole thing was trying to figure out a way to make it work. Unfortunately I dont's think there is, (that I can find yet).. I was kinda thinking about what Jason said and what would happen if I was to unplug fan? Just let the trap door open for air. That way its not being forced to try and light all the wood at once, What made me think of this was I started to load it after draft fan shut off, I just had the door open and the fire was just slow burn, as I added wood sticks, they were slowly igniting. Nothing was forcing air into it trying to ignite all of it at once. its was burning slow and low smoke. I did try and close the draft door some, but I think the fan just pushing air hard. 

[E Yoder]

Or try throttling the damper below the fan down... But watch for creosote. Slow burning can really do that.

[Crhall]

After playing with it for awhile I got it burning as clean as cord wood (or pretty close to it) Put one or two pieces of cord wood right in middle, then fill the sides and some over it while leaving the front grates wide open. Working nice for free fuel, thanks for all the help guys

[E Yoder]

Awesome! Free is great.