Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

what's acceptable ?

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 ?
Comments ?

and yes, there are CO detectors up in the office / lunch area
known to beat dead horses


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,368
    edited October 2019
    Your engineer doesn’t have a clue. I’ve had a few similar situations and had to do battle with the state fire marshal. Who much like an engineer, doesn’t like to be told they are wrong.

    No amount of backdraft is acceptable. It simply means the exhaust fan is putting the building into negative. It’s probably doing it while the burner is running too, affecting combustion is a negative manner.
    Makeup air is needed anytime the fan is running, period, otherwise it’s going to get it from the place with the least resistance, the flue.
    The barometric damper's main purpose is to control the draft over the fire.
    -Bring in make up air anytime the exhaust fan runs.
    -Completely enclose and seal the room where the burner is located, and bring in its own combustion and make up air.
    -If possible switch the burner to a balanced flue burner. Then you have combustion air and exhaust piped to the outside, and no barometric damper.
    -hackish option, but should be on every flue anyway, put a blocked vent switch on the flue pipe. At least it won’t let the burner run if it’s not drafting.
  • Jamie Hall
    Jamie Hall Member Posts: 22,050
    What @STEVEusaPA says. A very dangerous situation. Your "engineer" lost it on the first strike -- when he suggested changing the air settings on the burner. And then it got worse.

    I hope your CO detectors are the low level kind -- 1 to 2 max -- otherwise you're going to kill somebody with that setup.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England