Sorry to be so long getting back to the forum, I am not on the computer everyday and things can get hectic and many days go by before I can get back on. And then there is so much new stuff to read! Like the stuck grate! I just read that thread 'cause I had some close calls but have been able to muscle my grate and get past the thing.
Yes the smaller Hitzer 55 has a baffle with the direct vent damper. When closed (normal run postion) the gases have to flow down that baffle and pass within an inch or so of the burning bed and turn up after passing under it, in order to exit the stove.
I am now day 13 of a constant burn and loving it!
You mentioned blow backs and I've had them. I think I am avoiding them now, with a different technique. I only tend my stove twice a day, morning and night. After the fire freshens with the ash door open-I don't bother to change the auto damper....used to crank that up to high and then put it back, but don't bother anymore and leave it my setting for a 450F surface temp on the stove.
I "open up my stove" to do the tending twice a day. Open the spinner to 3/8" out or so, open the direct vent and open the ash door. Leave firebox door shut, of course.
When the fire freshens up to 550F I will shake and then stoke one side of the Hitzer and wait. Ash door remains open the whole process. I wait for the temp to dip, which it does due to the new coal and then come back up....and all the way back up to 550 at which point I open the firebox door and stoke the other side and close the firebox door and wait. The direct vent damper remains open thru out, like the ash door.
Wait for the second stoking of coal to get all the way back to 550. Yes, the auto damper is shut tight since my setting is 450 but I have found the fire getting back to 550 takes enough time to heat the coal and catch it and has enough time to drive off the majority of the volitiles that cause the blow backs.
So, after my second stoking and wait for the fire to come back to 550 I close the ash door. And I am very happy to report all is quiet re little explosions. There may be gentle "fluffing" but no puffs, no rattle of the auto damper! The first three to five minutes seems to be the crucial time. If I get by that period, there will be no puff backs. That's been my experience now for several days and "tendings".
Let me say at this point, that the advice to never cover a coal fire completely with new coal is right on...the flames of the burning coal act as "burners" for the volitile gas that accumulates. But I think we have a different situation with our Hitzers in that even loading one side, let it catch and load the second side does not prevent blowbacks if the fire hasn't had time to burn off the volitiles, because...we can have all the nice flames in the world but when we close the ash door, they are going to settle way down as the auto damper is still closed! The air supply from the spinner is important and having the direct vent open is important, but if the fire isn't hot enough, the volitiles will build a bit and get ignited causing the unwanted blow backs.
So, I've found, so far, I get no blow backs if I wait after each stoking for my fire to get back to 550F stove temp, which takes 15 to 25 min so patience is required, but it's worth it for no blow backs.
So, after the second stoke and climb to 550 and shut the ash door, I wait for the cool down....direct vent is open and the spinner remains open. It can take 20 min or longer for the temp to drop to 450 where the auto damper finally opens to take control. At that point I close my direct vent damper and close the spinner down to about 1/8" open and I am done for the next 12 hours.
I am one very happy coal burner at this point!