Are you replacing an existing hood and duct with one that provides more CFM? I don't know about Massachusetts, but in most states MUA is only required if a hood draws 400 CFM or more. Many higher capability hoods can also be jumpered so the blower capacity stays under 400 CFM.

Bruce

@Bruce in Northern Virginia we may want to go over 400 CFM on the new hood, so I am trying to figure out what that would involve.

In a custom hood you can hide MUA inside of the same hood. Otherwise have to have an opening somewhere and electronic damper. Some areas require conditioned air, then You will need some equipment for that.

We have no ducting in our house but no obvious place in the main floor to put a MUA vent. Do people put these under cabinets? On a wall? In the basement and add a floor grate?

Yes anywhere in the same room

MUA needs to go into a utility area adjacent hall, etc. it should not be located in the kitchen. It introduces too much turbulence.

@User, how close to the kitchen is too close? There is a mudroom adjacent to the kitchen about 10 feet from where the range hood will be. There are no other utility spaces or halls with an outside wall.

It depends on the volume, and overall home layout. You need an on site pro.

Thanks, @BT. I wonder what my old fluid mechanics professor would say about the claimed airflow in that system, especially if the front burners (normally the powerful ones) were on. I doubt the flow would be so laminar, especially where the two flows run into each other at the front.

You can do it under cabinets, just open the toe kicks (add a black screen). Or on a wall. Or in the ceiling. You don't necessarily need an electronic damper, a barometric may do. You'll need inline heating if you are in a cold climate.

>Thanks, @BT. I wonder what my old fluid mechanics professor would say ... laminar,

LOL, I TYP let DW[wife] decide... She cares more about these things. My general thought are about cold air not hitting my feet.

But 9" removal duct = 64" sq in cross, 3"x36" = 108 sq in cross. That looks good.

The goal of this contraption is to capture the biproducts of combustion [not required for electr] and escaping vapors & grease. 24"x36" face = 860 sq in. Probably 10x. [Well I do not know the true size of this filters]

I found this website listing design conditions http://www.eng.utoledo.edu/~akumar/IV/SampleProblems/Week5.htm

It appears to suggest 1.52" or even 2.5" WG... That is pretty turbulent, but our TEL is pretty short. Overall It will do what it was designed.