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Barometric draft regulator and understanding it. Please Help

Joseph_4 Member Posts: 275
Although I have been servicing gas boilers for years and went to oil service schooling about 8 years ago, I only get about 1 to 3 oil service calls per season on oil cuz usually most have contracts with oil companies. This summer I decided I wanted to get better at oil service. I am trying to understand how the barometric draft regulator works. I am dealing with a job now that the boiler company says is experiencing problems due to bad draft. They told me they want -.01 or -.02 negative draft over fire and want like -.04 at the breach which should be measured with my instruments at 18 inches above boiler but below regulator. I have a Field control 6" regulator and see the way to adjust the weight. This was not my install..Either I'm starting with a brand new Barometric Draft regulator.

Here is what I don't understand-- If I set it up today with todays outside and inside temperature... or today is a windy day.. How will it work on a less windy or colder day?
Joe Hardoon
HHI Servicesv LLC


  • RayWohlfarth
    RayWohlfarth Member Posts: 1,518
    Joe, I have an article on Barometric Dampers on the site under commercial heating. Hope it helps. Here is a link:
    Ray Wohlfarth
    Boiler Lessons
  • captainco
    captainco Member Posts: 796
    On oil, the barometric is set for the draft over the burner -.01" to -.02". I prefer -.01". The draft at the outlet should be -.02" higher. -.02" is the pressure drop of the heat exchanger or sections when the equipment is firing correctly and clean.

    The barometric controls the draft inside the equipment. When the draft in the flue, above the barometric is -.03" or -.04" the barometric will be closed depending on which draft you set it up for in the first place. As the draft above the barometric increases, the barometric damper automatically opens to relieve the excess draft, rather than pulling it through the equipment. This means once the burner is set up for a certain O2 or CO2 reading it will not change as draft changes. This gives up stable combustion. Without a barometric combustion is unstable, whether it is oil or gas. The outlet pressure of all equipment controls venting and combustion air to the burners. For some reason that concept is usually not taught by anyone except maybe Timmie and myself, especially on gas.

    Single acting barometrics are antiquated and not as functional as double acting. When an oil burner lights in most cases the barometric slams closed. Why? Because light-off is a small explosion that creates an initial positive pressure, which needs to be relieved. If not, it can cause blowback on the burner. Single acting barometrics are not airtight and therefore still blow soot and fumes into homes if there is no draft. If they were all double acting and we installed spill switches on them everything would be much safer.

    Because single acting barometrics were first designed for coal and wood spill switches wouldn't do much. But whenever something is "that's the way it has always been done" nothing seems to change.
  • Joseph_4
    Joseph_4 Member Posts: 275
    Awesome info Ray and Captainco.. I appreciate your responses.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    edited October 2017
    @captainco are you suggesting we start using double acting baro's on oil with spill switches? Pooooof! And soot every time that oil solenoid energizes and burner lights.

    Is that code compliant? I'm honestly curious, we just do double acting&spills on gas conversions.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • captainco
    captainco Member Posts: 796
    Unfortunately double acting barometrics are not approved by Code.
    But rarely is anything intelligent approved by Code because most Codes are written by persons that have never worked in the field.

    The only thing that comes out the barometric at light-off is air. If there is soot or smoke coming out at light-off it will come out a single acting because they are not exactly airtight. The problem with the single acting is it is not effective if we want to put a spill switch on it to shut things down when there are restrictions.
    I don't remember how many times I have seen the flue restricted past the barometric and the burner keeps running and sooting up the building.

    How often do you see the barometric slam shut when burners light?
    This has caused damage to the barometrics and made them stick.

    Remember I said the barometrics were initially designed for coal and wood. They didn't have an explosive light-off. Okay, so you throw a little gasoline on them first:).