I don't know how I to direct this thread. While I have a certain history and feelings toward manual pipe dampers, once again, "I'm no expert".
Growing up, everybody that I knew, burned coal. Some had coal boilers, some coal hot air, some Warm Morning parlor stoves, some had "bucket-a-days" for domestic hot water, in addition to their other heating unit, some had only coal kitchen stoves, etc..
The thing that they all had in common, was that they all had manual pipe dampers (MPD). The automatic barometric damper was NOT anywhere to be seen. The baro damper seemed to come along later, when the oil burner was introduced.
The MPD was typically opened during coal loading of the stove, it was opened to get the fire "cookin'", it was probably opened to shake down the ashes ... to let the dust escape up the chimney. Once the fire was going good, the MPD was closed to some extent. This seemed to keep the heat in the stove and also controlled the burn of the stove. The MPD is typically smaller than the diameter of the stove pipe it's mounted in, plus there are holes through it's center, so even "closed", there was quite an area for hot gasses to get by it and go on up the chimney.
Fast forward: I put the addition on the house, with fireplace on the first floor and a flue to the basement room for ?? wood or coal. The fireplace works great! The basement flue has "issues". I couldn't burn wood, as I'd get a downdraft, when the fire got weak. Changed to a Russo coal stove, which was better. The installation instructions said to use a baro damper to "preserve the warranty" and to set the baro for a predetermined draft in the flue. However, it was very temperamental . .. sometimes kindling or newspaper wouldn't even burn. Then after getting it burning, I might find it had gone out, for no apparent reason, leaving the coal sitting there unburned. The next day the situation might be exactly the opposite, with everything working like a charm! ... Very frustrating.
Last winter, I did extensive remodeling, including a new floor over the old worn , drafty one. Generally, things seem to work better this year. .... but far, from what I remember about "the good old days".
So, early this season, I added a MPD, which IMHO, has made a big, positive difference. (I've been asked to insert "caution warnings" into this thread, where appropriate. I'm not sure where that would be.) The thing with burning coal is, "common sense is an important issue", but more importantly "lack of common sense" is a bigger concern. I believe, I'll add here, "that even good common sense, sometimes falls short, if you don't know what the hazards are"! The MPD shouldn't be totally blocking the pipe off, and if the correct size is installed, that shouldn't happen.
I'm going to stick another "CAUTION" in here. The following are my thoughts, observations, musings, etc., applying only to hand fired stoves.
I think, a baro damper serves to control the draft over the fire, only! Part of a stoves ability to burn properly, is based on the building's air availability for it. If a ton of air is entering the baro damper, to maintain the correct draft over the fire, both heat and potential combustion air are expelled. (The same as running a bath or kitchen fan). Without adequate combustion air, I think CO possibilities are stronger, than with a good combustion mix. I'm not saying to eliminate the baro damper! I have both installed.
I think, with the MPD closed a "sensible amount", there is less fuel burned and less heat expelled through the chimney. In other words, the whole system can be run cooler, while getting the same heat from the stove. Also, I believe the coal has a much cleaner burn.
I think, with the MPD closed a "sensible amount", the fire stays warmer and won't extinguish on it's own, leaving a "plate full" of unburned coal.
While I was "down the road" getting coal from the dealer, when I walked into the scale house, I felt the stove, which was idling along. The guy there, who wasn't super "old", but wasn't green behind the ears either, offered his thoughts, without me even asking. He said, "Hand fired stoves needed a MPD to work properly and efficiently. And they wouldn't work right with only a baro damper." I asked him about CO poisoning. He said, "Years ago, of his coal customers, there was one death and a couple taken to the hospital. One was due to the elbow on the back of the stove being blocked up and the other was due to a furnace or stove, which was rusted out. Both of these customers had been told about the smell and unsafe conditions."
Hand fired stoves can be as safe as any stove. But they are intended to be looked after on a regular basis. There are many things, which effect the burn and safety of a stove. ... the more of them, that you are aware of, the safer it will be. CAUTION! If you were to consider a MPD for your installation, understand it first and if possible, have somebody, who is familiar with MPDs, guide you along with it's operation on "your stove". All stoves, their operation, and burn characteristics are different.