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Flue gas reversion or "bad propane"?

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  • Zman
    Zman Member Posts: 7,569
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    Shalom said:

    All this discussion of where the combustion air comes from is starting to make me wonder. I have two hot water heaters and two boilers (well one's broken right now) and they get all their combustion air from whatever happens to be in the basement, and exhaust into a chimney. As far as I know there's no intake from the outside, other than what comes in through a naturally leaky 98 year old house. Should I be concerned about this?

    I would only worry about it you decide to make your house less leaky or if you decide to install a 1,200 CFM commercial kitchen hood. I think it is important to remember that all combustion air comes from somewhere. I prefer to control where it comes from as opposed to letting it find the path of least resistance.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    CanuckerRich_49
  • Zman
    Zman Member Posts: 7,569
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    I've had this math running around in my head for a while as I think about pulling air from the space vs outside.

    If you are burning 100,000 btu/hrs on a 20 degree day and you pull your air from the conditioned space:
    100,000 btu/hr = 100 cf of gas and 1,000 cf of air.
    That would work out to be 16.7 CFM.
    16.7 * 1 (air density correction factor at sea level) * 50 Delta= 833 Btu/hr (sensible) to heat the combustion air.

    On that day you theoretically give up .83 % in efficiency. In reality, if you were to pull the cold CA from the outside, your boiler will run less efficiently so it may be a wash...
    Now my head hurts :|
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Leonard
    Leonard Member Posts: 903
    edited April 2018
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    I don't know much about fire efficiency but:
    Seems since ultimately all air comes from outside, not too much difference between heating that air directly with fire in burner or using inside air that your heating system already heated.

    Seems only difference would be the ~80 % efficiency of heating system in heating the inside air. Which sounds like approximately 20% times 833 Btu/hr = 166 Btu/hr extra loss. If oil ~ $0.003/hr extra cost maybe ???

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