please read my narrative, and comment on my last line(s).
consider this a peer review of sorts,
the maintenance garage where I work has been recently renovated, adding additional floor space needed for lawn equipment and trucks and such,
and an office / lunch room above,
about 900 sq ft added to existing 3500.
Also added is an exhaust fan, for ventilation. don't know the spec off the top of my head,
and an OA intake duct with motorized damper.
SoO is during scheduled Oc, damper opens, makes end switch, and allows fan to exhaust.
And then there's an Oil Furnace, large residential type, with barometric on the vent stack.
So with the building closed up tight, like for winter, a draft is felt from the baro.
engineer of record first tried to say the air shutter on oil burner needed to be opened / adjusted to force more air up the vent,
I challenged that high, or higher pressure(vent stack), would go to low(building, by means of baro damper),
combustion readings were taken on both sides of baro(?? !!), if I remember correctly, CO was only around 22 / 24(?),
how does this matter?
It's still being drawn into the shop !
I feel this backdraft when furnace is off and cold, AND when allowed to fire and hot, burner running.
I've had it locked off, and will switch and lock out the exhaust if this isn't corrected going into heating season.
So here's the questions,
Is any amount of backdraft acceptable? even if being drawn out by exhaust fan?
I vote NO, and that I need a draft inducer on the vent after the baro,
or powered OA make up fan, balancing the exhaust, to create a slight positive building,
and that NO amount of negative building pressure is acceptable with the open baro.
What's my engineer thinking ?
and yes, there are CO detectors up in the office / lunch area