I agree the soot buildup is due to burning bit coal but the Warm Morning design is optimized to burn it. I hoped that someone had figured out how to reduce it in these Warm Morning stoves. We both have the same sense that there are subtle details of these stoves that will allow us to operate them better once we know how.
Thanks for sharing your experience burning the bit you had access to. With regard to the bit coal I burn, I like the fact it has no sulphur smell and that it produces a little bit of small blue flames after the volatiles and yellow flames burn off and regard them as an indication the coal I have available is pretty decent quality. The 523 model holds 1.75 cubic feet of coal. Not sure how much that weighs but I'll figure it out next week and re-post.
It appears our stove designs are very similar. The model 523 has the rectangular draft door on the bottom door and access to the shaker handle when the bottom ash door is open but no lever to control the draft. This stove's design has a compression spring that provides tension against the draft contol plate to allow the draft to be fine tuned. The top loading door does have a sliding 'top draft' control to supply air at the top when burning a wood fire and I also keep it closed when burning coal.
Are your firebricks in good shape? Two of mine are cracked and need touched up with mortar. Are you keeping tabs on your flue temperatures? I have paid more attention to my thermometer and is seems to be burning between 200 and 270 most of the time.
We had a great Thanksgiving holiday, thank you. Almost everyone headed back home this afternoon. My oldest son is staying through next Thursday and we are trying to extend our holiday vacation a bit longer with him, except he is going to help me load up the truck with another ton of coal on Monday. Hope your family had a good holiday together too!