The inflow of air into the hood via the room and nearby counterspace is best when it has as low a level of turbulence as feasible. Also, it should get to the hood via all open sides so it doesn't act like a transverse draft. Ideally it would be laminar flow from a perforated wall across the room as used by the CARB for hood testing. But that is likely over-kill and certainly impractical in a real kitchen. If I were working with your configuration, I would try to direct the MUA across the ceiling away from the rangetop and allow it to fall into the room and spread on its way back to the range.

You could mount a large (maybe long and narrow) diffuser* above the cabinets (is there a soffit?) aimed to achieve the desired flow direction. Or it could be embedded as part of a "cabinet."

Be sure that the exterior MUA source is well away from the hood exhaust. Ideally at least 10 ft distant, upwind, and lower.

Heating MUA takes some space, so consideration for placing that, if necessary, needs to be an early decision.

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*A diffuser differs from a register by having longer fins, usually adjustable. The scope of available types may be found in the Hart & Cooley catalog.

So in the situation I described, the air would basically fall down from the bottom of the back corner of an upper wall cabinet. And the center of that duct would be just over 5 feet from the edge of the rangetop, to the right, along the same wall the rangetop is installed against. Is that just not going to be ideal? or is it going to significantly inhibit the functionality of the expensive ventilation system I am installing for the rangetop?

I don't have a soffit...I suppose I could just put a diffuser in the ceiling ~12' away from the rangetop on the other sideof the kitchen...problem is that would dump outside (probably cold) air right on our main entertaining area.

The only other option really in the running is to enlarge a 4" dryer vent duct I have to make it 6" and run that (maybe with another 6" next to it) along the roof of the basement and just dump the outside air into the basement where it would become sligthly conditioned before mixing with the upstairs, or I could run it up and through the toekick under the sink...but the sink is only about 3-4' away from that first proposed MUA drop-in. so I dont know if thats worth all the trouble.

I dont have the money right now for heated MUA, and I dont know how often in the winter I will be running the hood on high enough to warrant it. A benefit to the run in the basement is I could always retrofit with heat down the road....I dont have the space for heating MUA if it comes in anywhere other than the basement....

Although I don't do it myself for various architectural reasons, I am a fan of basement entering MUA because a room heater of sufficient power can usually be installed there (electric or hydronic) to temper the air without having to design specifically for duct air heating. However, toe kick entry into the kitchen needs to be large enough to not be a major pressure loss in the MUA system. I.e., sufficient toe kick area, perhaps equivalent to the hood entry aperture area, needs to be provided.

Also, the toe kicks used shouldn't be right onto the cook's toes. There was a forum member here who had a turbulence problem with the toe kick MUA entry blowing across a narrow inter-counter gap to hit another island/peninsula where it was directed up next to the hood space. The turbulence at the hood caused significant plume disturbance to the point that capture was seriously disrupted.

That all said, if the cabinet dump out of the bottom were via diffusers that could throw the air across the room instead of at the hood, then room mixing and air slowing would be possible. Nonetheless, if a basement path is the only one that can be heated, I would plan for the future if I were you and use the basement.

Note that if a basement wall is available for a duct, then a 10-inch duct placed in the wall with a 45-degree or greater cut outside to provide a rain shield would do as a basement entry. It will need a damper either balanced for low pressure opening or electrically controlled by sensing hood air flow (or hood motor power). A screen should be placed at the entry.

boy do I wish I had an HVAC installer...

Pinebaron,

Can you please elaborate on your MUA system? What manufacturer did you end up using and how do you heat? Thanks

The20KVa ElectroMechanical MUA has a built in 20KVA heater and all electronic programmable controls built in. Heat, output, fan speed,

fresh air damper, inlet/outlet temperature and air flow sensors de all built in.