That looks like a great start!! The only suggestion I want to make is to move your primary air channel down closer to the floor, I'd say around 6" to 7" up. For all the faults in the CB E-2300 that I have, I've recently come to a realization after 5 years. Their original design had it down around 6" off the floor. Problem was they did not make it cleanable. I CAN'T STRESS CLEANABILITY ENOUGH!!! My air channel deteriorated after only two to three years. Last year (season 4) I had a welder help me with a new channel using pipe. Air flow was no longer a problem, but my fire was too centralized around the nozzle and didn't burn well enough on the sides, thus bridging was a problem. Also I got a lot of puffing (kind of like a backfire). I actually had charcoal blast it's way out the chimney a few times as a result if you can believe that. Boiler is located in a building with metal roof and I heard the coals land on the roof. Freaky for sure. I'll attach the picture of that design. The second picture gives a little peak at the old channel. If you look close you can see all the build-up of ash and creosote inside the old channel. Sadly, like I explained earlier the new channel did not produce a stable fire.
So I decided to try another change, but I have not taken a picture of it. I came in through the back wall like before with a 2" nipple to a verticle"T" with a bushing at the bottom so there is still a drain for creosote (very important to consider) and some air can blow from there also. Short nipple up to another horizontal "T", sized down to 1 1/4", then pipe to each side and elbows forward along each side. I ran the channels up on top of the old channel for support. First I tried it with my outlet holes aiming mostly downward instead of straight outward like they had it, thinking this would also allow for creosote drainage. Problem with this was it burned the coals right out from under the wood. So I aimed the holes up some, not all the way. Basically at or just above the nozzle area. This thing is burning better than ever!! Good consistent fire, clean with very little smoke and minimal bridging issues.
The guys I've seen on here with the P&M 250 seem very happy with performace of those units. I've never seen one so I don't know how much it differs from the CB E-2300 design. The way I see it with my unit having the lower air channel is that it puts a nice even flow of air over the whole coal bed.
Good luck with your planning and building. Looks great so far. Keep us all posted!!
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