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Make up air....................(Starch)

JJ_4 Member Posts: 146
Are you sure there is not an existing Make Up Air unit. These are typically required, and interlocked operationally, if there is an exhaust hood over gas cooking appliances. If so, you may be able to modify to provide the extra 760 CFM make up.


  • Joe Brix
    Joe Brix Member Posts: 626
    I'm bidding a job......

    ....for a kitchen addition to a local bar/restaurant. They are installing an exhaust hood over the commercial dishwasher. It is spec'd as a Cook Model ACE-D, and supposedly can exhaust 760 cfm. I need a way to provide some type of make up air for this, and quite frankly am stumped.

    Does anyone here have any experience with this type of situation?

  • m slocum
    m slocum Member Posts: 10

    They make a short circuit hood which brings in it's own air.
    Another option would be an air handler with reheat coils that maintain a constant discharge air temp.
  • Glen
    Glen Member Posts: 855
    MUA -

    If other gas fired appliances are affected MUA may be required or it could be a building code issue in your area. This could be passive eg, like combustion air or forced via a unit on the roof. My favourite would be EngAir. So chat with your gas inspector - he/she can point you in the right direction. In this case it would be better to ask permission rather than plead for forgiveness.
  • Brad White_9
    Brad White_9 Member Posts: 2,440

    I would be cautious about the direct-to-hood make-up unless you temper the air. When raw cold air comes in, the condensation will be unbelievable, unless the hood septum is insulated.

    The inverse of this is, if you do temper the air (usually by code to within 10 degrees of space temperature), you might as well distribute it in the space and get some cooling/ventilation benefit out of it. For heating, you are looking at about 50 MBH load.

    Given that it is not a grease application (falling under NFPA-96) you might offer as an extra a variable speed or 2-speed setup. Leave it on low as background exhaust then boost when dishes are in production.

    Here is another idea to check out: If the kitchen is an open plan, you may be able to take the make-up air from the dining area if allowable by code. Use the ventilation air they presumably already have in there and leverage it to your benefit for no additional energy penalty. Do an air balance diagram on paper and identify all "inflow" and "outflow" sources. Grille hood, dish hood, toilets, etc. and see what "net" you need to make up.
  • Weezbo
    Weezbo Member Posts: 6,232
    hoods need to be short circuited...

    or the workers feel uncomfortable ...

    often there are coolers or condensing/additional sources of heat in the room, thought there is bring in additional outside air to mix some of that heat into the equasion... pipe a small MAU in addition to and drop it in , in the area behind the fire we were discussing the other day, that areas air moves across the space bringing both make up air and some Heat *~/:)
  • Dave_4
    Dave_4 Member Posts: 1,405

    I believe the OP is referring to a dishwasher, so I don't think a compensating hood will be spec'd.

    The model number you gave was for a fan, not a hood. Can you get us the hood model?

    For a hood exhausting a dishwasher, the simple solution would be to supply makeup air via gravity means; eg put a cap on the roof and some duct down into the kitchen and let nature do its thing. Ideally (and this part is beyond my knowledge) you would calculate the duct size to furnish slightly less than 760 CFM.

    Good luck,
  • Brad White_9
    Brad White_9 Member Posts: 2,440

    I would stick to using a fan. There is probably another source of exhaust in that kitchen and if left to "gravity", the dish hood becomes a path for induced intake air.

    You can get hoods with make-up faces by the way, but I agree with you that a simple canopy hood is the most cost effective basic way.
  • Joe Brix
    Joe Brix Member Posts: 626
    The \"hood\"....... being custom fabricated. It is for a dishwasher only. The fan I mentioned earlier will be mounted above the hood, on the roof.

    This place is used primarily in the summer, so cooling is more critical than heating. I am concerned about just dumping or blowing in untreated air, as this could cause excessive humidity and discomfort (has anyone ever really been in a COMFORTABLE restaurant kitchen in the summer?) during the dog days.

    I doubt that enough passive air is available from the rest of the building, but I'm probably a bit out of my league to say that for a fact. I'm almost thinking that some type of mau with mechanical cooling will be needed. Any suggestions for manufacturers?

    Thanks for all the replies so far, too!
  • Brad White_2
    Brad White_2 Member Posts: 188

    Aaon is one (lighter weight aluminum construction too). Reznor for gas fired applications (cooling options are not their forte' but they may have something now). Greenheck or Cook may have something too. If Cook does, I would keep it in the family.

  • I was just looking at MUA units by Reznor they do have cooling units. I happen to need one myself but for heat.

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