I have one in my shop and get 4-6 hour burn times with coals lasting up to 3 days if filled with hard wood after a load of soft wood. It should be noted that I can not get these kind of results with soft wood or if I'm only burning the stove for one load of wood. It requires at least 2-3 loads over the course of a day working in the shop to get lasting coals.
The first thing I did was to sh*t can that bi-metal spring and make the door flapper manual. Second I modified the ash pan door air dampener to close fully and tight, then marked it so I could know where it is adjusted to. Third thing was to remove the back plug and install an 8" chunk of pipe with a ball valve on the end to meter the flow. The pipe was just to keep the valve away from the heat so it wouldn't melt the nylon bushings that seal the ball inside.
Now my burning process is as follows:
Starting from a cold, bunt out stove, I will rake the ashes around in the bottom to remove any excess ash. I always leave about 1-2" of ash in the bottom to plug the grates and insulate. Next I open the ash door, dump the ash pan, replace, and then scrape a small hole in the front of the ashes to allow air from the bottom for starting. Now the stove is ready to fill.
I usually keep a good mix of hard and soft wood on hand so usually I'll start the stove with soft wood. Load two large chunks on each side as far back as possible leaving a gap in the middle. Fill the middle with thinner splits of dry soft wood or kindling. Continue to fill the stove 1/2 way making sure to leave the front open and keeping the smaller dry stuff in the middle. Now fill the front with your starting material. For me it's paper then splitter scraps, bark, or small (1/4-3/4") pine or cedar chunks cut at about 2-4" long placed vertically. I keep some 1" square chunks of Ash, Oak, or anything straight grained to place above this. Next I'll toss a couple more thin splits in the middle/front above this to catch when the kindling is lit. Top it off with one more big split and light.
To light I close off all the top fire air and light the paper at the bottom with the ash door open. Let things roar as the kindling catches with the ash door open. After a couple minutes I'll close the ash door and open the ash door dampener one full turn. Open the feed door draft flapper fully and let the fire catch. I have a thermometer in the chimney that I'll moniter from here. When the inside stack temp gets up to about 1000*F, I'll close the feed door draft flapper and fully open the rear air valve that I previously mentioned. This is where the stove runs most of the time. When it is below zero outside I will have to close the rear air and the ash door air to 3/4 to slow down the draft some. Leaving ash in the bottom of the fire box prevents most of the air from coming in the bottom. After the first load, the bottom grate is usually completely plugged leaving only the rear air valve as the inlet. I have found this to be the most efficient I can get the stove to burn.