Been wanting to try and mix some coal with the wood and see if it can help burn time and cut down in wood consumption. So went yesterday and bought some and would give it a try. I have 10000E Heatmaster. With these cold nights I have been filling it full trying to get 24 hour burn cause I leave for work at 4 in the morning. So yesterday I filled stove just under half the way full and put in a 5 gallon bucket of coal in with it. Peices of coal averaged baseball to softball in size. Made sure they are spread out and on top if the wood to get the air to burn right. That was at 4:00 pm. I told my oldest son to go check the stove for me at 11:00 am. Said the temp was at 183 so it is still holding temp. I thought it would be good if it would hold till I got home at 5pm. Check the stove when I got home temp was at 179 with fan running so I opened the door just to see how it looked. Fire was going good and still had wood and could see the coal burning to. Raked everything around to even it out and fire got so hot I had to stop and shut the door. So I let it go for a while and check it again later. Went out at 9 and the temp was at 157 opened the door and it needed some attention so I put in the same that I did yesterday to see if I can get the same burn time or if it was fluke!!! That was 29 hours on half full stove if wood with coal added to it. If I can get these results with these temps being this cold I will be mixing all the time!!!