I am burning Blaschak nut coal in my Harman Elite Magnafire insert. After numerous attempts to start the fire, I have finally succeeded, however I can only keep it burning for 10 - 12 hours. My goal is to heat my home with this insert. Am I choking the fire by putting too much coal on it after it has a good burn going? I also need to keep my lower vent door open or it does not get enough air and goes out. Is there too much ash content that would smother the fire? I do the shaking of the grate as per instructions. My coal is angled high to the back of the insert and lower to the front of the door. How much coal is a full load for this insert? Is 25 lb adequate? How long should this burn before I refill? Would the "refill" be another 25lb? I would appreciate any comments from other users. I seem to be stumped.