I am completely new to coal/wood burning.
I am having trouble with my Johnson furnace. It is very similar to the Norsman 2500. The furnace is set up in the garage and the 8" stack goes straight up 16' single wall and then another 12' in double wall (near the ceiling and outside). I have a MFD in place also.
I started buring wood first, but I couldn't get a long enough burn (4hrs max). I know part of the problem was the wood I was using. Wood is gone. Got injured and can't split more at this time. So, I decided to try coal. I was told that I need to burn lump (2-6") coal in the furnace by a local coal supplier. My furnace is designed for both. It has bottom fed air and shaker grates. The coal I got is from the Knighthawk mine in southern IL and it is called called raw coal. It is bit coal and ranges in size from dust to 2 foot square blocks. I got it because it is $55/ton. I am located in central IL and the lump coal around here ranges $245-$280 a ton. Brought back 4 tons. 3/5ths is chunks and the rest is fines.
The problem I am having is I can't keep a good hot burn going for any length of time. I tried loading the furnace every way I can think of. All big chunks, all small pieces, mixing them together, differnt sizes in layers, etc. I have even tried getting a good set of coals going, pushing them to the back and then loading again so it has to burn accross the pile and not just from under. I usually get the same overall results. The coal starts burning like mad (flue and ash door open). Leave it until flue gets to about 400-500 then turn the MFD to half way between 1 and 2 o'clock. This slows the fire some and I wait a little longer to close the ash door to make sure there is a good bed of coals. I then close the ash door. If I don't the furnace stays too hot and the coal is gone is just 2 hrs. I have tried playing with the air adjuster on the ash door and the MFD, but a couple hours later the flue temp is down to 250 and won't get any hotter.
In the morning, I have two full trays of ash and about 2-3 gallons of clinkers. This does not include what is taken out during the day. There is not enough heat to restart the fire. Total time 6-7 hours. House is cold.
I'm sorry for the long post, but I am tring to give as much info up front as I can.
P.S. I've done some searching on here and tried some of the tips others have given, but I always get the same results.