I would like to make one final comment on this drama:
AS I posted earlier today - my edumakation does not hold a candle to the lucid engineers that lurk here
I submit - you all need to get your HEAD OUT OF the chimney and back in the boiler room
It doesn't make any difference how good the chimney is occasionally performing when it is doing so above expectation - it is however VERY important that it does perform well enough in all climates and events.
and "well enough" is all it takes to put a draw on the smoke pipe [ connecting the appliance to the chimney] in the area of the correctly installed Barometric damper - These examples posted about balls or a satchel of man parts; have NO relationship to real world smoke. The are based on the assumption of infinite air movement on both ends and are being performed in a lab environment.
On your appliance - this is not the case at all -YOUR NOT IN A LABORATORY - your air movement potential is LIMITED by the size and condition of the smoke pipe and when the correctly installed Barometric damper is wide open - it [ the baro] will pass the CFM required to fill the smoke pipe it is attached to and drop the atmospheric pressure [at that point in the pipe] to pascal value you have it set to.
There ISN"T enough Volume at atmospheric pressure in the boiler room to feed it - IN THAT INSTANCE - now think :>0 -- where is the MANOMETER taking its samples from??????
IT AINT THE CHIMNEY - its the appliance vs the room
The boiler that is in a room [apparently in you example above] is under negative atmospheric pressure and the manometer is registering TOO much draw - ON THE APPLIANCE
--WHY???? because there isn't enough make up air to offset the over functioning chimney and the baro is trying to keep up but your choking it by not giving it what it wants -- AIR
- [ back to justification] ONLY a fixed amount of air or volume or CFM will pass in a specific smoke pipe because thats the size of the pipe -- just like only a specific amount of heat energy can be moved in a fault tolerant manor in a wet heating system ----> if we are moving too much water we change the pump
if the chimney is working too well ---- fix the chimney
a second hole [barometric or mechanical or transcontinental intergalactic] in the smoke pipe will not solve the issue that the appliance is operating in the wrong environment!
and with that let me just add