Berlin wrote:A baro reduces draft the appliance sees by allowing a controlled amount of room air to enter the stack, this not only cools the flue thus reducing draft, but, breaks the draft to the appliance directly by allowing the flue to pull air from the room thus reducing vacuum in the flue.
A larger baro is necessary to break excessive draft because the ability to reduce the draft is directly related to the cross-sectional area of the baro's maximum opening. The change in pipe size has nothing to do with it, it's the size of the baro that's important. There's a forum member in niagara falls who went from about a 9" connecting pipe to something like 18" dia. T with a huge 18" baro and then back to 9" connecting pipe and to the stack. The stack was an interior stack over 40' high in a large old home in niagara falls and it still pulled that baro almost half open when the wind hit. When you have a situation with excessive draft, forget about mpd's + baro (you don't need it) all you need to do is use a large barometric damper to keep draft regulation automatic.
please excuse a newbie to these concepts and practices but, i am having a time getting my mind around the idea of using a Baro. that's twice the size of the outlet flange.
at the surface it seems nothing can be gained because if you have a 12" baro. set at say .07 - .08 if it opens 1/4 of the way it might be equal to a 6" unit pretty far open ? so the house is still loosing warm air faster than the stove can keep up ?
OR, is it the case that there is such a large area of 12" "T" and reducers that the flow leaving the stove has to fill it ( thus loosing speed and draft power) and the larger baro. is hardly able to open ?
if i think of this over a lengthy period i MIGHT figure out what happens, but i consider myself teachable, and the wife has other things for me to do than sitting a staring into space.