As I stated, I've don't have much of a problem with dead spots or bridging in either of my Harmans. I'm able to clear the ash in the Mark I pretty thoroughly by just shaking as I indicated above; I chose not to. My problem is that the Mark I is installed in a tile chimney that has such a strong draft that a small child or cat could be sucked up and never seen again if not watched carefully.
I know what a "horrible" problem to have.
That stove is in a very small space, maybe 400 square feet and I can't close the air controller far enough and yet get a widely dispersed burn with just that. I've found that by using the ash to retard the draft and having the air controller open a tad wider, I get a more uniform burn throughout the stove and have a better handle on the heat production. I burn Pea coal exclusively in that stove for the same reason.
I'm extremely happy with how the addition of the Mark I has worked out. I can run both stoves cooler and yet burn the same amount coal as last year for an over all warmer house. Fortunately, I don't have any of the negative side effects that were spoken of in other postings here. The bottom line is I'm a happy camper with how my stoves are burning. Take care, Lisa