Fire: I agree with what you say. The Chubby certainly has it limits. Perhaps when you pushed it, it became inefficient. I discovered it has a sweet spot for my installation, with the MPD closed and the air door open 1/8 inch, resulting in a nice steady 12 hour burn on 20 lbs of coal with 1/2 fire pot left so no danger of going out. This for me raises the temperature of my main floor by 40 degrees over the outside. When it is 30 out, a typical Cape Cod winter temperature, it is perfect for me. When it is colder, I choose not to fire the stove hotter (but I could), but instead I light a wood fire in a second fireplace. The fireplace has an insert with a blower that claims to be 40k BTU/hour, probably some fake number but it throws out all the extra heat I might want on a cold night. Who knows what the chubby is 50-60k-70k BTU/hour, does not really matter as normally the stove is not run at this level, although Larry told me of a guy once that ran his at 900 with no issues except he needed an occasional grate replacement! It seems clear that you need/want far more than 40lbs of coal heat per day and the DS Machine can deliver if you feed it!