Cold weather update: The stoker is doing very well. With the added area around the firepot rim, I'm getting a much more complete burn of the coal. The added area of burning coal extending out on the perimeter ring is increasing the heat output because the coal can burn much longer before falling off into the ashpan.
The boiler maintained 150* water temp all night, appeared to have burn about 80# of coal, the ash pan about 2/3 full, not bad for 12 hours of burning in -10* weather with a wind. I don't believe my hand fed fire would have maintained the water temps after 10 hours. Gotta love a stoker.
I have noticed one slight issue that I will take care of soon. The steel ring I added is about 1" below the top lip of the firepot. This is so that the ring is below the row of air vents feeding the fire on the ring. The bed of burning coal is very fragile, it doesn't take much to disrupt the air flow through the loose pieces of rice coal. What is happening is the burning bed of coal fractures when it goes over the lip of the pot and drops onto the steel ring. Once the ash builds up on the ring then the burning coal bed stays more intact and expands in area instead of fracturing.
After looking at the EFM style burnpot, I've decided that I need to bring the steel ring up level with the top lip of the pot, so the coal bed will stay intact as it is pushed out onto a level lip like the EFM firepot. The trick is going to be to channel the air from the outer ring of combustion air vents up to a steel plate 1" above the vents. I have a plan and materials. I'll post a photo when done, rather than trying to describe it here.
So I'm going to pull the stoker out, and fire up a hand feed fire, to burn up the remaining nut/stove coal mix. this will also make room in the coal bin for a load of rice and or buckwheat coal.
I'm not real excited about making another hand fed fire but I do need to use up the remaining coal. I'm really enjoying the stoker doing so much work for me.