Oh dear... Here we are at the MPD vs Baro argument
I agree some room air does go up the chimney with a baro as where no room air is lost with a MPD. This room air causes cold air infiltration from outside. Its difficult to justify how much
goes thru the baro door. The million dollar question, How much of a percentage it amounts to when compared to the total air infiltration that a house already has. The baro is a valid cause of cold air infiltration but is it enough to discount a baro?? This is the shade of grey in my opinion..
I've noticed that for me, the manual damper doesn't hold a set pressure as flat as a barometric. My heat output still tended to yoyo, and I was still constantly tinkering with my primary air control to even It out. How much coal was I wasting by heating the stove more than it needed to and does it equal what I saved in coal when it wasn't heating enough?
I believe a coal fire makes best use of the available oxygen when it isn't constantly flared and then let to cool down but instead its allowed to burn with a constant oxygen supply. A baro helps aid with this consistent burn. I see it when I'm monitoring my temps thru the burn cycle.. After initial burn off of volatiles, the temp will fall (after closing the load door) then over the course of about 3 hours, the temps will increase about 5%, then plateau and stay there till tending time again. During that 3 hours, the draft pressure is a steady -.03, primary air is untouched but temp grows.. What's the only conclusion? More of the available oxygen is being used. This is very important. Our atmosphere is 80 percent nitrogen. That means 80 percent of the air going in is just there to carry heat out the chimney. The more of the available oxygen that can be used means more heat output per loss of heat due to nitrogen carrying heat out the chimney and those ratios are huge
If I had to pick one or the other, that MPD would be on its way to the scrap yard at $.08/pound.. Since I think the benefits of an even draft outweigh air infiltration caused by the baro. Buts that's just my opinion and its hard to prove.
Truth is there are many variables and its difficult to justify if the overall effects of one trump the overall effects of the other. I think that's why everyone is so passionate about which one they choose and for what reasons. Me, I use both to maximize the benefits of each. I think MPD and Baro get along just fine on the same pipe
I'm intrigued with the science involved with operating a hand fed. I'm so glad I didn't start with a stoker hahaha