My way of saying we don't have enough information: If you are heating one room house that is 12 feet by 12 feet and has R-48 insulation, something is wrong. If the stove is in an open barn, you are expecting too much.
I'll venture a guess you are somewhere in between. It sounds like the stove is running about right, but without more info, such as doing a heat loss it's just hard to say. Give us an idea of how much area you are heating, how well it is (or isn't) insulated, and how much and what kind of coal you are using & I think we could help.