In reverse order: I think the Fantech MUA is available with heating. Check with Fantech. If not, a heater can be provided by someone. I use a "radiator" connected to my hydronic heat system, so I didn't need to research heater suppliers. Also see graph below. The input value is 800 CFM. Look up BTUh vs KW to convert. (Click image to magnify.)

The pressure losses on the hood blower are the hood baffles, the ducting including bends, and the imperfect make-up air pressure vs. outside pressure. I would just assume 2/3 of rated performance, else you need to get ModernAire to provide a pressure loss vs. flow rate curve for the hood and we estimate all the rest of the losses.

2/3 flow rate is about 800 CFM, which is more than needed for 90 CFM/sq.ft. of hood aperture, and since the blower can move that at more than an inch of pressure drop, I think your choice is conservative.

P.S. @clinresga: Forgot to say 'Hi.'

And I forgot to answer the salient question about MUA introduction for your case. You may wish to search for various MUA threads here to tune up on ways to insert the air so it doesn't cause too much turbulence at the cooktop and spoil plume capture. Every architecture is different, so advice is hard to give that has any generality.

If introduced into the kitchen, a floor diffuser would likely be a food bit collector, so I would use a large set of toe kicks or the accessible side of a partly blocked off cabinet. Air in the kitchen should move away from the cooking area, and in particular, not onto the cook or the cabinet in an island or peninsula behind the cook as the MUA reaching the cooktop area will be turbulent.

If the crawl space extends over the house area, dumping into wall cavities with diffusers that are somewhat away (in an adjacent hall, say) from the kitchen should help stabilize the air flow.

I'm not sure whether there is a low cost way to cool MUA. Best may be to oversize the household a/c to try to compensate. Note that the graph above also can be used to estimate cooling required.

The MUA ducting paths need to be at least as large in sectional area as the MUA system uses, 10-inch diameter, say, and the diffuser area should probably be at least twice that to keep down pressure loss.

A silencer on the MUA may be helpful, just as on the hood system.

Since the days you were here more frequently, there have been some long hood threads you may want to check out if you haven't caught them all:

https://www.houzz.com/discussions/5161173/hood-faq#n=101

https://www.houzz.com/discussions/6099827/exhaust-hood-faq-ii#n=113

https://www.houzz.com/discussions/6040827/range-hood-noise-project

https://www.houzz.com/discussions/5888450/seeking-muas-advice#28657635

and @opaone's opus:

https://bamasotan.us/range-exhaust-hood-faq/

Depending on the size and location of openings, introducing makeup air into an adjacent hallway may not meet the prescriptive code requirements (2018 IRC M1503.6.1):

"Kitchen air exhaust makeup air shall be discharged into the same room in which the exhaust system is located or into rooms or duct systems that communicate through one or more permanent openings with the room in which such exhaust system is located." Introducing makeup air into the return of an air handler is permitted, but it will likely result in a grossly oversized system with attendant higher initial cost and lesser performance. Our climate zone (IECC zone 4) is the same as north GA. Our experience is that there is no need to condition makeup air--in summer or winter months. I suppose there might be a need if cooking times are lengthy.

Can't we assume that a hallway connected to a kitchen meets the requirement so long as there is no door between the hallway and the kitchen?

It depends on how the inspector and/or code official interprets the code. A telephone call by the mechanical contractor to the code official before committing to a location will serve the OP well.

Agreed. What I fear is that the code inspector will not realize that poorly conceived MUA introduction may degrade capture and containment, thereby defeating the whole point of kitchen ventilation.

The code isn't concerned with kitchen ventilation nor the efficacy of a range or cooktop vent hood; the prescriptive code doesn't require one. Rather, the concern is depressurization of the home and consequences of that.

The pressure equalizes at the speed of sound among all connected rooms, less frictional losses getting there and air inertia affecting transient air flow to fill any pressure "dips" (near the hood). So any hall open to the kitchen should do as its cross section is much much larger than that of the MUA ducting. Of course, the feed to the hall needs to be relatively unrestrictive relative the the MUA ducting.

I would add that large blowers, such as my Wolf/NuTone 1500 CFM rated down-roof blower, have significant time constants from turn on to full flow -- several seconds to 1/e of final flow. Nearly any passive MUA should keep up, and active is a matter of design and tuning. The alternative is to pressurize the house positive, like large buildings, and I don't think that would be a good idea for nominal home construction without some serious pro/con analysis.

As you may see from threads here, I am a fan of MUA for combustion appliances, thereby greatly reducing the effects of imperfect MUA to kitchens. (By which I mean appliance MUA increases the allowable pressure drop that would cause back-drafting of combustion appliances.) Any kitchen MUA, whether active servo driven blown or passive "hole in the wall" will have to work with some difference in pressure.

So, @clinresga, what is your combustion appliance situation, and do you have a fireplace?

kas--thanks!! Appreciate the callout from the old days, and the homework assignments! Sorry for delayed response, was on vacation and elected to ignore kitchen ventilation issues for a week.

Super helpful discussion of my issues Issues in my place. Glad that my thoughts on choice of hood and blower seem adequate.

As for appliances that are impacted by negative pressurization: two fireplaces: a direct vent in the open family room adjacent to the kitchen, and a conventional wood burning fireplace in the living room, open to the family room Everything else (water heaters, heat pump furnaces) are electric.

Locations for MUA air returns are a big question. Since the kitchen is contiguous to, and open to, the family room, there is really no wall space in the kitchen. Ceiling returns would be prohibitively difficult to run up through walls from crawl space. I agree that floor returns are undesirable as catch basins for debris. So I think I'm restricted to low wall returns either in the family room or the adjacent hallway which opens directly into the kitchen without any door. If I read the code cited by CRH above--"into rooms or duct systems that communicate through one or more permanent openings with the room in which such exhaust system is located"--it would allow discharge into the adjacent hallway.

Agree that while code may be primarily aimed at negative pressurization, effectiveness of the actual kitchen ventilation is the point to this entire complex, expensive enterprise, so locating returns properly is critical.

Hadn't thought of silencer for MUA, another good thought.

Great to have a chance to rejoin this community again for another project. Thanks!

We try to introduce (unconditioned) makeup air in the kitchen near ceiling level--up and out of human traffic flow. If you don't have a lot of wall space in the kitchen, consider framing a duct chase at the end of a cabinet run or designing the cabinetry to accommodate a duct. That would enable you to run a rectangular duct from the crawl space with a termination near ceiling level.

The MUA system could be mounted in the attic and draw air from the roof. Then a ceiling diffuser is feasible in the kitchen or hall.* If in the kitchen, best would be near the hood but aimed (via diffuser design and blade angle) across the room so when it "circles back" it will be relatively less turbulent. Is there an aesthetics limitation on another roof penetration? Room in the attic?

Electro Industries seems to make MUA systems and MUA heaters: https://electromn.com/make-up-air/

Accurex also make MUA systems, but they seem to be only commercial, so I'm not sure whether they would support a residential request.

If you want MUA to keep the kitchen pressure up such that none of the fireplaces are back-drafted, no matter how many are operating, your MUA will probably have to be controlled via differential pressure sensing between kitchen and outdoors, via scaling from hood motor current, or via hood duct flow measurement.

_____

* See Hart & Cooley catalog. https://www.hartandcooley.com/assets/files/1p3/hcb_851530_residentialgrd_catalog_ed11_nov2018_web.pdf

I don't see my 3 ft x 3 ft uni-directional diffuser in this catalog, so it is probably in the commercial catalog: https://www.hartandcooley.com/assets/files/1p4/hcb_851531_grdcommercial_13ed_sept2018_web.pdf

In any case, you can also find wall grills in these that may be useful for non-ceiling configurations.

Thanks CRH and kas. Issues: it's a two story house, so running duct down from attic very difficult--I'm already struggling to run exhaust ducting to roof as prior install used puny 6" ducting and I'm having to enlarge a chase all the way up. So more likely MUA in crawl. I'll have to get with contractor to brainstorm ways to return the air.

kas: re controlling MUA flow, the Fantech unit (which I am quite predsiposed towards based on familiarity with their exhaust blowers) uses a controller .Their website describes it this way: "Each MUAS comes equipped with a Fantech Makeup Air Controller (FMAC). The FMAC provides automatic operation of the Makeup Air System. The makeup air flow rate automatically and infinitely varies proportionally with the speed at which the exhaust is operated by the homeowner. A neutral (balanced) pressure scheme is common, but the installer can also employ a slightly positive or negative pressure scheme should it be desired." This suggests it does pressure sense in some way, though I'm not sure of the specifics.

kas and CRH: thakns again. Re locating returns for MUA, it's a two story house and I'm already strugging to route exhaust ducting up and out--having to enlarge a small chase that used to contain inadequate 6" ducting all the way to the attic. I don't think I can find a route to get return air ducting down from attic through second floor to kitchen. So I suspect I'm left with crawl space location ducting somewhere--I'll get with my contractor to brainstorm locations.

kas: re controller for MUA system, I'm very predsiposed to the Fantech system based on familiarity with their exhaust blowers and the seemingly straightforward ordering and installation process. Their website describes how the system is controlled thusly: "Each MUAS comes equipped with a Fantech Makeup Air Controller (FMAC). The FMAC provides automatic operation of the Makeup Air System. The makeup air flow rate automatically and infinitely varies proportionally with the speed at which the exhaust is operated by the homeowner. A neutral (balanced) pressure scheme is common, but the installer can also employ a slightly positive or negative pressure scheme should it be desired." I'm hoping this addresses the goals you outlined.

Seems like it. Ability to be slightly positive or negative suggests a pressure sensing scheme.

All right, sounds good. Will meet with contractor later this week and give you an update--thanks to both of you!