Furnace or boiler??? heating air or water??
Just to make sure we are using the right nomenclature... do you mean a hot-air furnace.. or a hot water [or steam] boiler???
For a Furnace,, the choices are few,,Keystoker and Harman.. and non of them are 150K btu, [that I remember] but come close..
For a boiler, your choices are several,, EFM, Keystoker, AHS, AxemanAnderson, Harman and a few more..
If you are looking for a forced hot air unit,, a Furnace,, the best way to accomplish this is to use a Hot water boiler,, and use a water to air heat exchanger in the hot air plenum in the existing furnace's ductwork.. A boiler is a more controlable heat, stores residual heat, and also easily heats your Domestic hot water, which is roughly 30% of your heating bill..
There are dozend of threads on this subject.. grab an Iced Tea, or your favorite beverage and read a few pages of the stoker forums... There is a wealth of information to be read..
All The currently available coal stoker boilers and furnaces are good units.. stay away from US Stove products at your TSC, Hardware and Home Depot,, they are not good coal burners..
Hope this helps... Greg L