hotblast1357 wrote:Well wether its from underneath or above its a bypass
I've been thinking about how to answer this, here's what I've come up with..
Lets call this case #1 - A pipe that is bringing secondary air from under the grates to over the coal bed will need motivation. The motivation is pressure. It will be relying on the pressure difference between those two locations.. I measured the pressure above and below the coal bed to have a difference of .005" of WC with the negative pressure under the grates to be stronger. I took the measurements directly after a shake and load by inserting the mano probe in under the grates thru the primary air intake with the ash pan door closed.. I'm thinking the coal bed generates the extra -.005 just by its own mechanism of heating the incoming primary air and forcing it to rise as it flows up thru it. As the grate collects ash and slows air flow thru the coal bed this difference changes. It becomes equal, then further into the burn the negative pressure is stronger above the coal bed than under it.. Its at this point the pipe would begin to bypass the primary air meant for combustion and route it up over the coal bed.
Case #2 - Now if the secondary air is ported to the outside of the stove you have a pressure difference of -.03" WC or possibly more depending on how you have the baro set, up to -.05" WC.. So you see this pressure difference could be 6 to 10 times more than in case #1. And should (on paper) make a HUGE difference in the amount of secondary air getting in over the coal bed.
What I'm getting at is that the secondary system in case #1 will be totally dependent on the conditions inside the stove, mainly the coal bed - where in case #2 its completely independent and controllable. In case #1 there is implication that the pipe may take air from above the coal bed and route it back under the grates since negative pressure is stronger there right after a shake and load (and with the ash pan door closed) , making it run backwards
then later in the burn cannibalize incoming primary combustion air.. It will depend on how much primary air is allowed to come in under the grate.
So, I realize this is all on paper lol and things that look good on paper don't always work in the field..
and I realize there is a lot going on there.. Some may read this and think it don't make any sense at all but the numbers have some merit and should dictate how case #1 behaves.. Try it and see what happens..