The Clean Burn system has no catalyst, no treatments, nothing, it just burns the oil extremely efficiently. I have a Clean Burn CB-2500 in my shop, the thing runs great, and heats out 10,000sq-ft shop without issue (although ceiling fans help keep the heat off the 14ft ceiling). I even have a separate tank rigged up to it with a ball valve that will let me run on WVO (WVO and WMO do some weird things then they start mixing, so its best to keep them in separate tanks. We burn ATF, WMO, WVO, #2 - #5 heating oils, and Hydraulic oil in the system, and the only time we get a complaint is when we burn old fryer grease... The Perry's Ice Cream Plant behind us has a few guys that keep yelling at us that they get hungry when we burn it, the exhaust smells like french fries and beer battered fish, or occasionally roasted peanuts. They are obviously just joking around, but they can't even tell when we are burning motor oil or anything besides the fryer oil, its that clean. We've had it installed for a few years now, and our exhaust pipe is just barely starting to get a tint to it.
Without a doubt, I wouldn't burn the stuff in an OWB. First of all, our oil is all filtered before its burned so heavy metals and what not don't end up in the exhaust, and second, we don't burn the sludge. We have to drain off all of that once every 2 years or so, and that goes to Noco Oil company, for whatever they do with it.
Don't give the wood burning guys a bad wrap, just use paper to start the fire, and don't soak your wood with anything but elbow grease!
