the baro dampner's flap swings open and allows air to be sucked thru it instead of thru the stove (coal bed) when a big gust of wind blows across the top of the chimney. SO with that said, as the wind passes over the top of the chimney it "sucks" the heat and exhaust out faster. the baro is a self regulating flap valve that allows the stove to burn consistant.
it saves coal and maintains a even and predictable burn...... I feel thats important for im away from the house 10-12 hrs at a time and would hate it to come home to a dead stove cause the windy day gobbled up all the coal....
i feel its worth it to do it right the first time! if you dont need it cover the opening with foil
I would like to add that it keeps the draft steady not only for wind, but also temperature variations outside. When it warms up outside during the day, it will close as the chimney draft weakens and when it gets colder at night, it will open when the chimney draft gets stronger - keeping the draft for the fire consistent.
The yo yo-ing of my furnace temp was due to a run away train effect. As my furnace grew warmer, the chimney drew harder which caused the fire to run hotter, which made the chimney draw harder still, till it finally couldn't draw any harder and my house was 80 degrees. THen I would cut back the combustion air and the furnace would cool which would lessen the chimney draw, which would cause the fire to run cooler still, which would lessen the chimney draw even more.. I think you see where this is going
to a cold fire... ANYWAYS - the baro cured all of this