Sunny Boy wrote:[quote="Lightning"]Yes sir, I follow that but since the pressure is lower in the stove doesn't it stand to reason that combustion air is being pulled in? Or should I look at it as if the pressure outside is higher so it's being pushed in?
No forced draft, all natural.
Then yes, it's outside higher pressure that forces the air in. Thinking that lower pressure inside the stove - "suction" - makes a stove work means that suction has to be "something", when it's actually a lack of something - a lack of pressure.
And, I'm sure your glad to know that when your stove is working right, . . it doesn't suck !
Um, vacuum effect, hence why check dampers work the way they do.[/quote]
You have to think about energy and where it is. There's no energy in a vacuum, so it can't do work. The work can only be done by pressure.
Check dampers only work by making an opening in a heat system to allow cooler, heavier air that is outside into the heat system. The cooler air lowers the temp of the hot gases making them heavier, thus less pressure difference inside vs outside. With less pressure difference, there's less force to push air in and flue gases out, so the draft slows down. With the decrease in incoming air volume ahead of the firebox, the fire dies down producing less heat.
Remember, vacuum is not "something" either. It's just a word to describe a lack of air pressure. Auto mechanics often use the term vacuum as if it was something, but a carburation engineers calls it "pressure drop", which is a more accurate way of saying what the force is that is actually in play.