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What is the definition of

Tim McElwainTim McElwain Member Posts: 3,904
Make Up Air?


  • earl burnermannearl burnermann Member Posts: 126
    make up air

    is air brought in from the outside to supply enough oxygen for combustion.
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  • billbill Member Posts: 429
    My take on it is ...

    that the term Make up air is air forced into (Fan) say a commercial kitchen, to compensate for the huge airflow through those huge range hoods. This as opposed to the term, combustion air (Just a hole in the building).
  • HDEHDE Member Posts: 142

    Makeup or compensating air is outside air which is introduced into the building to replace air that is exhausted from the building through ventilation or combustion processes.

    A make up air unit will normally involve a mechanical means
  • GordyGordy Member Posts: 7,122

    What HDE said only add a controlled mechanical means to prevent negative pressure in a dwelling where controlled combustion processes take place that get their combustion air from with in the dwelling, and are vented to the outdoors.
  • Bob HarperBob Harper Member Posts: 732

    2009 IRC G2403 General Definitions

    Air, Makeup. Air that is provided to replace air being exhausted.

    [me] This includes combustion, dilution and excess air through combustion systems but it also includes air exhausted by fans such as kitchen hoods, dryers and fart fans in bathrooms. There are several specific places in the code, such as M1503.3, which require MUA. This this case, it is referring to exhaust hoods >400 cfm requiring dedicated powered MUA interlocked with a damper and sized to equal the exhaust.
  • Tim McElwainTim McElwain Member Posts: 3,904
    I encourage my students to

    think about it this way, Make up air is the air required to replace air removed by mechanical exhausting. This is not necessarily combustion air as more air in addition to make up air may be needed to sustain combustion on oil and gas fired appliances. This is where we get into the two opening rules etc as air for combustion.

    The make up air may be replaced mechanically or it may be an opening sized a certain size based on appliance BTU and CFM. A gas dryer is an example that may need makeup air.
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