Definitely something wrong with your draft. The combustion blower needs to be on all the time for the coal to burn and to burn efficiently, the damper plate should be 1/4 to 1/2 open. If you are pressurizing your fire box with the blower's plate barely open, the exhaust is not making it into your chimney. Seeing as how there was already a draft inducer installed provides evidence the draft was a problem before you took over the reigns.
Like others have said, manometer, manometer, manometer, coal stoves should not be run without one!!!!!! Having one for spot checks is good, having one permanently installed is best. CO detectors are also important, sounds like you have that covered, and keeping the stove clean is a must. For both safety and longevity of its corrode-able surfaces, which includes but not limited to, well, every dang surface that fly ash touches!!!!!