Yes, I run both stokers at the same time, but only when one stoker can't keep up with the heat demand. That is when it stays a steady 20 degrees or lower outside. My house is 3700 sq.ft. So, I have a lot of area to keep warm. I've been playing around with the combustion air and it seems that as long as I'm above idle, the combustion air can be wide open. It is at an idle speed that I have to lower the combustion air, so the fire doesn't go out.
I generally hand fire if it is above 40 degrees. I have another Clayton sitting right next to the stoker Clayton, ducted into the same duct work plenum, to handle either light loads, free wood, or very cold below zero temperatures, together with the stoker Clayton being fired at the same time. It is an awesome seen to view when everything is firing on those below zero nights, with the wind chill at -20, and you can run around the house in nothing but your underwear. The kids and the wife love it.
Constant coal fired heat is so much more comfortable than the on heat and off heat of the conventional fuels. Stay always warm, keep American workers receiving a pay check, by burning American anthracite, in American made coal appliances!