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Hey man, how about this as something easy to try? Hopefully your barrel isn't too big a deal to remove. If that's the case this is a pretty simple thing to implement to see how it goes.

Cut a 6" hole in the barrel as low as you can and plumb an exhaust bypass straight into a T in the bench exhaust. Put a damper in the bypass. Start up, heat up your chimney, slowly shut down the bypass to get flow through the bench. By closing it incrementally you should be able to control chimney temps, speed up flow through the bench, and fix your condensate issue. Put a kitchen thermometer in the stack so you can get a good idea of exit temps, up at the thimble, and keep it above 220° or so. Put the whole bypass at the surface of that existing cob work so you can cover it with a bit of cob for sealing around the barrel exit.

You might even get hotter bench temps this way.

I dunno, just a thought.

From reading your other posts, Manny, I'd suggest cleaning the chimney before venting the hot exhaust into it directly from the core...

Thanks for the help, guys. That's a neat idea you've got there, Matt. I like the idea of running a primer like that. I don't know that it's something I'd do during the peak of winter, but this might be an option later on. I'm a little leary of cutting a hole in my barrel right now. Kind of a "if it aint broke, don't fix it" mentality, I guess. I'm still confused about where all the crud comes from. I get the idea of the reflux column and the temp. change at the cold chimney, but is there really that much crud in the exhaust? And then in a traditional stove this crud just gets carried farther and drops out across the landscape?

I definitely appreciate your concern, Oddmar. I tend to be a bit anal about keeping my pipes clean. I get up on the roof regularly to brush off the snow on my water heating panels and that's usually a good time for me to check the chimney stack and run a brush down it if needed. I'm not getting much gunk in the chimney, though. Just the little black dust bunnies in the elbow at the bottom.

I don't think you have creosote, I've seen the burn temps on your barrel and your stove burns clean. I'm sure of that. I believe you are condensing and the stuff is the tiny soot particles that are entrained in the gas stream. Fly ash, organic particles that are not combustible, etc. The exhaust condenses and runs down the flue picking up more stuff from the walls, and builds up at the collection point. Just a theory, but if you had creosote it would be manifesting much earlier in the system. And yeah, I totally agree with if it ain't broke, don't break it!

So back to this possible solution, what do you think about running this in 6" with an 8" stove? We still have the main 8" section so it should still work, right? Just tryin to save a buck since I already have a 6" damper. Also thinking I can run a water heat exchanger here just ahead of the damper.

Yeah man, I think it would be a go for sure. I've had really good luck modifying flow rates and overall performance with bypass dampers. I think it will probably be a slam dunk, now that I've had some more time to play with bypass systems I am convinced it's a good way to get gas speed up and thereby get higher temps throughout the mass, which in turn gets gas speed up.....and so on.