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is a power draft-assisted burner considered a "appliance with a draft control device"?

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Diamonddave
Diamonddave Member Posts: 10
in THE MAIN WALL
contradicting info from studying, is this type of furnace considered a "with a draft control device"? or is it an appliance "without a draft control device"?
my understanding is "a draft control device" is only a draft-hood or a barometric damper. however a RED SEAL sample test question seems to categorize it as a "draft controlled appliance" in pictured question, the only way to come up with B (157in2) is to calculate it as a "appliance with a draft control device"

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  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 11,753
    Test making individuals are sometimes not in the field and know what terms are used for the the common types of appliances we use. A draft control is the common name of a Barometric Draft Control. Technically anything that controls the draft at the exhaust of the appliance can be called a Draft Control. even a fan that regulates the amount of draft regardless of the natural draft of a stack or chimney.

    These questions are obvious to the person writing the test question. Not so much for the person in the field that uses different terms like Draft Inducer, or Draft regulator, or Draft Hood to make sure that we know the difference. In the 40+ years I have beed working on this stuff a Barometric Draft Control was a Draft regulator. However, in the last 15 years I started calling it a "Barometric" in the classes I taught so as to not be misunderstood.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    PGB1PeteA
  • Big Ed_4
    Big Ed_4 Member Posts: 3,412
    I think the question is asking to size the fresh "Air supply" for a 1,200,000 BTU input combustion ... I figured 120 in square and rounded up to B...

    There was an error rendering this rich post.

  • Bob Harper
    Bob Harper Member Posts: 1,146
    To 'control' draft, you must be able to regulate it up or down. Draft is a pressure differential- not flow. I always use the term 'draft pressure' to differentiate it from mass flow. A blower causes mass flow. On an inducer, the net effect is a negative pressure in the combustion chamber to make room for the expanding byproducts of combustion and excess air while drawing in combustion air. Once heat creates natural draft, its role is negligible but it does not 'control' the draft. Likewise, a draft hood allows dilution air, which inhibits draft pressure but it does not 'control' it. It kills the draft at standby, at low fire or high fire but at a relatively fixed rate. The only variable is how much air gets entrained through the fixed orifice of the net free area of the hood by the Bernoulli Effect, which shoots the flue gases up the stack where draft pressure carries them to the atmosphere--unless there is a negative pressure differential in the CAZ, in which case the hood can provide a pathway for spillage or backdrafting.

    You have natural draft or gravity venting or atmospheric venting, then you have induced draft as with 80% furnaces then forced draft with power venters.
    EdTheHeaterManPGB1
  • PGB1
    PGB1 Member Posts: 92
    edited February 2024
    Remember Thermizers from the 80's? They were sold as Draft Control Devices. I suppose shrinking the opening in the vent pipe, which is what they did, does qualify. Free CO meter with each purchase?
    EdTheHeaterMan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,891
    It is power assisted so size the MU air to the BTU of the boiler. Nothing is added for a draft hood or a barometric damper
  • Steamhead
    Steamhead Member Posts: 18,323
    PGB1 said:

    Remember Thermizers from the 80's? They were sold as Draft Control Devices. I suppose shrinking the opening in the vent pipe, which is what they did, does qualify. Free CO meter with each purchase?

    Looks like a very fancy Neutral Pressure Point.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Diamonddave
    Diamonddave Member Posts: 10
    edited February 2024
    as I'm writing my Red Seal exam in 2 weeks, i still currently do not know how to answer this question properly, all my studying is teaching me allot of wrong answers, everything I've learned so far about this scenario: draft controlled device; Draft hood of barometric damper
    not draft controlled device: no draft hood or barometric damper

    this question appears to contradict what i am studying
  • Teemok
    Teemok Member, Email Confirmation Posts: 757
    The test question is what your trying to understand. If you understand the math and it tells you what category a "power draft-assisted burner" is than that settles it. If "Power" means forced and not induced than there can very well be a barometric damper. Just worked on a 2 million btu Laars Pennent with twin fan forced 4 stage burners and a big barometric damper.
  • Eidolon
    Eidolon Member Posts: 1

    A little late for the OP, but maybe this can help others. In Canada, a power draft-assisted burner is called a fan assisted burner. These burners require a barometric damper (aka draft regulator) to help adjust negative pressure in the combustion chamber pressure. Thus, you would calculate for the combustion air using a draft controlled appliance.

    Using B149.1 code 8.4.2, you take the first 1,000,000 btus and divide by 7,000 btu/in2, then take the rest of it, 200,000 btus and divide by 14,000 btu/in2. Then add together.

    This gives you 142.86 + 14.29 = 157.15 in2

    I hopes this helps.

    PeteA

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