How to determine if original boiler was coal fired?

How can I tell if my house's original boiler was coal fired? I've been optimizing the one-pipe steam system off my 10-year-old gas boiler in my 1936-construction-date house, in Harrisburg, Pennsylvania. I have replaced the tiny main steam pipe vents with Barnes and Jones Big Mouths with the capacity to vent as much as the pipe can deliver to them. I have replaced all radiator vents, insulated a long branch main in a crawl space adjacent to the basement that some idiot had stripped of all insulation (probably to warm the floor above since the radiators were not keeping the room warm enough) and I am currently fixing sags in that branch to eliminate water hammer and speed the flow of condensate. I am already seeing big improvements. Now I am going after the smaller improvements.
The electric vent damper on the boiler stack had been set to the manual, always-open setting by a prior owner or service tech. When switched to operating/automatic, I can hear the electric motor trying to turn, but it does not turn, so I assume that the control motor is busted. I switched it back to the manual/always-open state. I intend to replace the electric damper, after reading many posts on The Wall that indicate that a vent damper on an over-sized, not-too-efficient gas boiler paired with a chimney designed for a coal-fired boiler will improve efficiency by keeping the boiler warmer during off-time. I know there is much controversy over the ultimate benefit of the vent dampers, but most of the threads I have read lean toward recommending vent dampers in the equation that I believe I have, which is:
Relatively inefficient gas boiler + over-sized gas boiler compared to EDR + chimney designed for coal fire = potential for efficiency gain by using automatic damper. The damper replacement will cost me just $75 and will take just minutes for me to install.
So I am trying to figure out how to determine if my chimney (external chimney) was designed to vent a coal-fired boiler. I do not see anything in the foundation perimeter that appears to be an old coal chute, although the window well window near the current boiler might have originally been for coal access. There is also no evidence of any sort of framing or walls in the boiler area that seem to be typical of old coal storage rooms. A chimney inspector deemed my chimney to be in excellent condition. Of course he tried to sell me on a stainless steel liner, and I understand the benefit of that and will eventually shell out the big money to have him install that. He noted that the chimney does not have tile lining throughout, but instead is tile lined only at the top. Down where the stack from the boiler joins the chimney, the chimney internals are just brick without a tile liner. Surprisingly, the brick and mortar appear to be in great condition, according to the chimney man.
One other item to note: the galvanized stack that goes through the basement wall and into the chimney is badly corroded, just in its horizontal section before it goes into the chimney. The vertical section into the boiler hood is in great shape. Of course I am replacing that corroded section, and I have several CO2 alarms, so all is good. I am intuiting that the wide-open draft damper is allowing too much cold air into the galvanized stack, it is condensing, and rotting out the stack. This would also lead me to believe that the electric damper would improve things by cutting down on cold air condensing in the galvanized pipe, keep the boiler warmer during off-time and prevent excess corrosion on the boiler from the cold air coming down from the chimney.
So there is my novel-length post, all to ask: how can I tell if my original boiler was coal-fired?