In order to "prove" that the advertising claim of 17 hours of 85,000 operation, all Harman would have to do is prove that it can be done ONE TIME and that ends the argument. Actually, it is the owner's manual that says that on p. 4. Neither the literature nor the website make this claim.
Since we have been doing a lot of spreadsheet calculations, here is another one.
As lime4x4 has previously calculated, a max feed rate of 8.75 pounds per hour yields 122,500 Btus of INPUT Btus with 14,000 Btu Anthracite coal. For agruement's sake (and there is a lot of that going on) let's find the absolute highest Btu Anthracite we possibly can.
In 1938, Harold J. Rose, Senior Industrial Fellow--Anthracite Fellowship at the Mellon Institute of Industrial Research, Pittsburgh Pennsylvania, published a paper titled Inherent Characteristics Of Anthracite. On page 30 of that paper, he shows Anthracite from the Southern (Lykens) Field to have the highest Btu content of the 8 fields he listed. That value was 15,237 Btu/lb.
As I said in a previous post, Harman does not publish the efficiency of the Magnum's heat exchanger, which I suspect is better than the 70% that has been used in this thread. I am going to use the 122,500 number but I am only going to use 85,000 Btus, since that is the stated OUTPUT of the Mag Stoker.
Target Hours is 17
Btu per hour 85,000
85k times 17 is 1,445,000 which is the number of Btus needed for 17 hours of operation
Best possible coal is 15,237 Btus per pound
Divide 1,445,000 by 15,237 to determine the number of pounds needed for 17 hours
The answer is: 94.83 pounds of coal.
Do I think that is realistic on a real world basis? Of course not. Have I suggested that Harman omit that statement from future editions of the owners manual? Of course.
Honestly, the old statement that "figures can lie and liars can figure" is true. If every industry marketing or advertising statement were challanged, the vast majority are exaggerations at best and outright lies at worst. Most people know that and deal with it. There are literally thousands of Mag Stokers out there working at this moment that owners would say they "are them some" stoves: they did everything the owners thought they would do, "and then some."
SMK