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Designing a Passive Make-Up Air System

mawiah | Posted in Mechanicals on

Hi! I am a DIY homeowner, who is in the middle of a planning project for a new kitchen which I am GCing myself. 

We are considering purchasing a new, 48” dual fuel range and a corresponding 1000-1200cfm vent hood. In doing my research, I understand that I need to supply make up air to compensate for this hood. 

We live in Georgia, so I am not planning on heating and/or routing this through my HVAC system, and instead am looking at a stand-alone, passive system using a 10” duct with automatic damper, etc. 

My question for you is whether it’s best to split the MUA system to be balanced on each side of the range, with outlets in the toe kicks directly to the left and right cabinets to the oven/range or one large outlet which is farther away, but would be in kitchen in a wall. 

The toe kick solution is frankly easier for me to access via basement, but I’d like to do two, 6” take offs from the main 10” trunk line to accomplish this. Possible?

Many thanks for your input. Make up air systems are the biggest mystery in home building/planning! Even my HVAC contractor wasn’t confident in what I was asking!

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  1. user-2310254 | | #1

    First, combustion inside a home is a bad idea. It would be much healthier (probably cheaper) and better for the planet if you went all-electric. But I understand that aesthetics sometimes trumps science and long-term self-interest.

    FWIW. The Home Performance channel on Youtube has several videos on this topic. See Corbett lives in the Atlanta metro, so maybe you could give him a call as well.

    1. mawiah | | #4

      Thank you. His video was very informative.

  2. Expert Member
    ARMANDO COBO | | #2

    Just to be clear, by code, you still need to provide a MUA unit for a 1200 cfm exhaust fan. As an example, a Fantech 1200 is not a small unit and does require some planning.

    From experience, if you don't want cold toes while cooking in winter, you may want to install the toe-kick vents under other cabinets not used regularly while cooking, and I would try to keep those vents with in 10'-12' from the exhaust fans to have a more effective air-flow loop. Fantech does sells heater units for their MUA units.

    1. mawiah | | #3

      100% aware that the system is required and that a 10” duct and damper is large. The good news is I have plenty of space and access to install and maintain it from basement, including filter box. The question really is whether having 2, 6” ducts off of a main 10” trunk will meet the MUA requirements for this hood.

    2. Expert Member
      ARMANDO COBO | | #5

      I think it should not make any difference. Watch to make sure your turns are round or 45° angle at least. Square turns reduces flow and increases static pressure.

  3. Expert Member
    Akos | | #6

    Here is a very detailed study that looked at MUA for commercial kitchens:

    Overall, the best setup was delivering make up behind the range. The next best was half the airflow delivered to a ceiling register at some distance from the range and the other half to the air handler in the restaurant.

    For a house, I would duct to the air handler and call it a day. This gives you good mixing in the house and some tampering to avoid the cold feet issue with toe kick vents. Make sure to use a damper that has rubber seals and near zero leakage.

  4. Expert Member
    ARMANDO COBO | | #7

    It’s my experience that one cannot apply what we’ve learned in commercial kitchens to residential kitchens MUA. For starters, commercial hoods are much bigger than residential ones, in fact, must cook’s heads are usually under the hood, and that never happens in homes. The exhaust fans are also a lot more powerful, allowing to capture the effluent more easily. The cabinetry and appliances are two different designs, builds and installs.

    If I had a new design I would supply the MUA in two supply vents located in the ceiling, within 10’-12’ away from the exhaust hood, but I never dump it in the air handler, as there is too much air-flow obstruction. 1200 cfm is a lot of air you must replace quickly at approximately the same rate as you’re exhausting, and a direct route is always best and most recommended by all MUA equipment manufacturers.

    Since Mawiah mentioned that his MUA would be installed in the basement, then it makes sense that the MUA would be much easier and economical to bring it through the toe-kick. Sometimes common sense applications are warranted.

    1. Expert Member
      MALCOLM TAYLOR | | #8


      Restaurant setups also take into consider how the movement of make-up air can cool the just cooked food as it's being plated if the intake is in front of the line.

  5. Expert Member
    NICK KEENAN | | #9

    I'm going to be Contrarian here, and suggest you look at an induction cooktop and a sub-400 CFM hood, then you can skip the makeup air. Unless you routinely cook for dozens of people that's all you need.

    1. mawiah | | #10

      That ship has sailed. Big 48” 6 burner, griddle, double oven. We need the big hood!

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