To measure the flue temperature, I use an antique Wheelco thermocouple galvanometer.
This solidly made precision instrument is probably 75 years old and was used in an oil refinery. It, and thousands of other valuable old items were slated for destruction in order to reduce the refinery's taxes. This one escaped destruction, but still wears the yellow paint of death. I cannot find any record of Wheelco. It is unfortunate that this fine example of American engineering is nearly forgotten, due at least in part to tax laws that encourage the destruction of assets.
After using the stove a few times, I realized that while it is a very good stove, it also had some serious shortcomings. When shaking the grates, it was impossible to shake them without having coal jam in between them. It was also too easy to go too far and dump the coal. I lengthened the link between the grates until it hit the sides if the grates were rotated more than 15 degrees. This has proven extremely effective. The shock of the link hitting the sides loosens the ash and makes it fall readily, while it is impossible for coal to drop down and jam in between.
Then there was no ash drawer. This was a serious shortcoming in a stove that is over 2 feet deep. Also, the ash door is surprisingly small. I couldn't do anything about that, but I did make a drawer as big as I possibly could. It has about 1/4 inch clearance all around. This was a huge help, but there remained one problem. Because the drawer was narrow, some ash fell along the sides. This had to be shoveled out. I took the stove apart and removed the supports for the firebrick. I drilled and tapped holes into them and bolted sheet metal ash guides to them. This gets about 80% of the ash that missed the drawer.
Recently I added a safety feature: An automatic closer for the main air door. Without that, I had to say close to the stove when starting, a process that may take more than a half hour. Coal can surprise you, for it may smolder at a low burn for a while, until it reaches critical mass. Then you can see stack temperatures approaching 1000 degrees F in a matter of minutes. Not a safe situation. My safety system consists of an electromagnet which holds the door open, and a thermocouple controlled alarm with relay contacts. When the alarm trips, the alarm cuts power to the electromagnet and the door drops by gravity. I like this because it is fail safe. If the power fails, the door will drop. If the thermocouple fails, the controller will alarm and the door will drop. Still, I consider this a safety backup only and would not intentionally leave the house and depend on the alarm. However, I could someday forget and this little thing just might save my house. Here are some pictures:
The temperature controller: An old Omega controller from my junk box. Also in the box is a Sonalert audible alarm and a 9 volt "wall wart" power supply from some long ago discarded electronic gadget.
The electromagnet has de-energized, and the door dropped. While the power is restored to the electromagnet as soon as the stove cools and the alarm stops, the magnet is far too weak to raise the door. In fact, it has barely enough power to hold the door up. Better that way. Any disturbance would cause the door to break free and drop.
The arm that holds the magnet is attached to the stove bracket by a single bolt which is aligned with the air door hinge pin. This way the magnet can be set to hold the door at any position, or even swung up and out of the way.
I believe Alaska Stove still sells replacement grates for these stoves. At least they did 6 years ago, when I replaced mine after acquiring the stove. This stove was badly abused and seriously over-fired, warping the grates and the firebrick supports along the sides. The front was warped too, and the door would not close properly. Since Alaska Stove did not sell the firebrick supports anymore, I had a local foundry cast new ones for me, using the old ones as a pattern. I straightened out the front by intentionally over-firing it without firebrick in the front. Then I pounded the warped front with a sledgehammer while the steel was soft. That worked well, and the door closes properly now.
I built a 6 foot x 18 foot coal bin that holds approximately 10 tons. Later I covered the bin with solar panels, in the process creating what may be the worlds only coal bin with solar panels.
I burn between 3 and 4 tons of coal each winter, at a cost here of $200/ton. That is like getting heating oil for less than $1/gallon, or propane for maybe 75 cents. However, the money I'm saving by burning coal is only part of the story. My house is much warmer with coal heat. My high efficiency propane heater delivered all it's heat upstairs to the living spaces, as it was designed to do. This however, left me with a frigid basement which was unpleasant to be in during the winter months. By contrast, the coal stove heats the basement to 80 degrees F. This heat eventually works its way upstairs, supplementing the heat arriving through the ducts. Because of the stored heat in the basement, the stove can be out many hours before the house feels cold. By contrast, when heating with propane, the house only felt warm when the heater was running. Yet, even when running the propane heater for maximum efficiency by turning the heat down whenever possible, I still had some January propane bills that were larger than my entire season when heating with coal.