Steamup, What you need to understand is with coal there is no standard for coal quality. Other fuels, home heating oil, natural gas, propane and electricity have known standards for the BTU content of the fuel. Therefore a standard test specification for BTU output vs. the fuel input can be created. These are the DOE or IBR ratings you see on boiler nameplates. This is not possible with coal, because the coal quality varies considerably. While it's a straight forward procedure to measure the BTU output of any boiler in the case of coal it's not all that useful. The boiler manufacturer could test with a very hot high BTU coal. Obviously the boiler would produce a corresponding large BTU output. For you if your coal is of poor (low BTU) quality, no matter what adjustments you make will produce the manufactures rated output.
While it is important to match the boiler size to your homes heat loss, there is a wide range of operating BTU output on any coal boiler. Also remember that building heat loss calculations are worst case calculations based on the coldest day of the year plus some margin. The design coldest day of the year is a possible but rare event. If the 130,000 BTU rating of the Coalgun is close to your heat load it will work. It just doesn't matter if it's a gross or net rating.