Introducing it into a utility area, or adjacent hall might work. But, your CFM calculations are likely low for that size cooker and island placement, and you will need HEATED MUA. Or else you can very quickly reach exterior temperatures as you exhause all of the interior heated air to the outside!

Thanks... appreciate the thoughts. We are trying to also manage the thermal losses, and agreed on the tempered MUA. Many times of the year we'll still only get up to maybe 50 degrees post tempering (and that is also a ton of energy). So the closer we are to the range, theoretically the less losses we would have, right?

What do you think we should be looking at for CFM, or how do you calculate that?

Make up air should be introduced at a location which doesn't compromise the effective operation of the range hood. That's certainly not internal to the hood. The 2018 International Residential Code (IRC,) which forms the core of most statewide building codes, requires:

M1503.6.1 Kitchen exhaust make up 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.

Our practice is to introduce make up air in the kitchen. We find there's no need for a make up air heater in our climate. I suspect you'll only need one during the coldest portions of the year.

Thanks, Charles. Yes, definitely intend to have the register within the kitchen or adjoining space, and that is good reference. I guess what is not clear to me is how to ensure I don't wan to compromise the operation of the range hood, while being as close as practically possible, so as to minimize heat loss.

Hi, rossn,

Here's a link to a good and very readable article on make up air for residential range hoods:

https://www.finehomebuilding.com/membership/pdf/8002/021232053.pdf

For what it's worth, we typically introduce make up air in the kitchen ceiling or in kitchens where the ceiling height allows, through walls near ceiling height and never into the HVAC duct system (I understand you don't even have one.)

Thanks for the reference Charles - I've seen parts of that article, but not the full thing, so that is good to see. Glad to hear you have had good luck introducing into the kitchen through walls near ceiling height, as that is the option I would have.

Assuming you have had fan-powered makeup air systems, what style diffuser have you all usually used, and how far away from the hood are you typically? I understand good care to not disturb the natural rise of the effluent/grease is important to not disabling the hood's function.

Thanks for your thoughts, kaseki. I have read a number of your responses to other threads, and know you have been pretty engaged in this area, so appreciate your support.

Understood about preventing turbulance at the hood. Being in a heating climate, I am trying to strike the balance between heat loss and ventillation. Ideally, the air would be introduced similar to what the architect proposed, but several commercial papers indicate the introduction of makeup air directly at the hood should only be a small part of the makeup air volume.

Below is a drawing of the new kitchen/dining layout. Provided I can get the county to accept me having an intake grille below an electrical panel (not acceptable per NEC), then the makeup air equipment reside in the 'dead' SW corner of the kitchen cabinetry (framed in and accessible from the adjacen bathroom), which would otherwise become unusable space. It would take in air through the outer wall, go through filters and fans vertically then turn and go above North above the cabinets (framed-in space), with silencer and heater. Then exhaust somewhere above the refrigerator. Based on your above comments, it may be best to have a large diffuser pointing North into the stair well, though I had initially been thinking a final elbow (after up sizing the duct from 10" to 14") or entering a plenum of sorts and exiting to the East (towards the range hood) to avoid a cold dining area.

If angle the north bound duct up and through the ceiling into the attic, I could turn east with larger ducting in the attic, but there is very little to no space there (like less than 3' at the peak) and then I would be losing heat into the attic, post tempering.

Also worthy to note is that the heating system in the home will be radiant panels on the ceiling.

Does the exit around the refrigerator area with a fan powered makeup air system seem like a sound approach, and do you think a diffuser pointed east would adversely affect the range?

Edit to add: Toe-kick is very hard to get to here, and my wife is not fond of colder air at the foot level, since we are often barefoot.

Your sizing approach for CFM doesn't appear to be different for island versus wall, but is in the same ballpark as where I had landed with the 1000-1200 CFM, which is good. Tricky question: does a 54" hood require more CFM than a 48" hood, over the same range, for the same cooking?

Thanks, Charlie. Agreed it is a tremendous amount of air to be moving through the home, especially unconditioned. And, that is an energy concern. The way I see it, the best I can do is get a good that has very good capture to minimize the amount of CFMs and makeup air needed. I would size for full load, but hope to not use the full capacity often.

The island is about 12' long, but some of it will be a butcher block top for prep so hopefully we can find a suitable slab for the rest of it.

Knowing what I know now, if I could go back and put the range on a wall I would do it, but the windows are already installed and options are lacking.

Addendum: Air curtain MUA depends on a suitable construction of cooking device, hood system, back and side skirts as needed. Such a design will have been tuned to the (usually) fixed air flow of the commercial hood that they are designed to operate with.

Some commercial set-ups dump the MUA at the floor to flow under the cooking unit and up to the hood. This also requires some care. In general, turbulence from the cook moving about, side drafts through the room, and the MUA can conspire to interfere with good capture and containment by the hood.

I think the "finehomebuilding" pdf is lacking in several respects.

Amount of heating based on MUA flow rate and temperature difference between outside and inside may be estimated from the graph below. (10k BTUh = 2.9 kW) It is possible with sufficient hydronic heating power to use a radiator type heat exchanger to heat the MUA via one's boiler using a separate zone. Electric heating is probably easier to install, and only requires enough ampacity (and wiring path access).

(click to expand)

Thanks, kaseki. Do you think in my situation an air curtain MUA re-introduction is practically possible, or that design is best left to a fully engineered solution (which won't be practically in reach for this application)? I am assuming, especially with the island, that this isn't practical.

I did see this builder's youtube video which was interesting, but seemed more like a short circuit hood than an air curtain, at which point I'm not sure there is benefit.

Fantech has a 10k electric unit. That sucker draws 40 amps at peak load, which is a little painful from an energy perspective, and would only give me a max delta of 25+ degreesF.

I will check with my hydronic guy to see if he thinks a hydronic heater feasible and cost effective... my concern being both complexity of controls and the 'what ifs' around potential water freeze, but likely I wouldn't run the range if power was out and certainly not the MUAS fan. I have a 2 temp system, with the higher temp being closer to 130F EWT. The boiler has plenty of BTU headroom and is beneath the area in question. As is electrical.

@rossn, you are singing my tune, on so many levels, so although I'm not a professional just a beleaguered remodeling homeowner, let me pitch in my tuppence. At least you will know someone nearby is walking a similar path! I too am installing a new kitchen in Colorado (the house is up in the mountains at 7000 feet). We're "only" doing a 36 inch induction cooktop but I do plan to use it a lot, for everything. It's on a wall unlike your island application. I've purchased a 40 inch wide by 22 inch deep hood insert that is 1000 cfm with an external blower, and a 1050 cfm MUA unit from Electro Industries. It comes as an all-in-one makeup air unit with heat tempering. I chose this because it was more compact than the Fantech units, and it's a small house.

We're placing the MUA unit about 25 feet away from the cooktop, in a place where there used to be a wood-burning stove and there is already a hole in the roof for that chimney. Unit will go in the attic and flow down through the ceiling. That area is now a utility closet, with a louvered door that will allow the air to move freely into the house without (hopefully) creating a draft. The whole area is an open space so once the air is through the louvers it's a straight, hopefully-laminar journey across to the kitchen, and will not cause effluents to go sideways on the cooking end of the space.

Looking at your drawing, and realizing that your system is going to be a whole 'nother order of magnitude bigger than mine (which BTW my small town contractor already thinks I am insane to be putting all of this in) I wonder if your proposed location near the fridge is still a touch too close? Is this a gas range? Which raises the issue of "sideways" flames...And yes, they were picky about my electrical panel and not putting anything at all under it. Maybe your inspector will feel differently.

PS - I have radiant heaters along my ceiling and loooove them :)

gg

ah yes... quite a challenge to work through, and good to know others besides me struggle with it :) I did speak to electro industries, but their 3 speed setting wasn't right for my needs. Besides dimensions, I expect that the home is going to tighten up with the remodel, but not excessively, such that it may turn out I only need 500 or 800 CFM and not full tilt. The fantech controller gives me some flexibility to not kick on until a pre-defined threshold.

I don't have too many options for physical locations, and have to also consider keeping the intake away from other venting appliance exhausts. So, I will have to make the location work out, but at least have the option of pointing the air into the stairwell, but worry it will cool down the dining area too much.

Yes, the range will be gas. And I can probably technically justify the installation of the inlet grate if recessed into the brick, but that goes against the spirit of the NEC rule, and so i'd want to get them onboard. They realize that remodel has limitations and are often willing to work on that front. While most of the NEC is based solely on safety, I think this particular rule is around preservation of future panel changes, rather than safety.

Nice to know you love the radiant ceiling... definitely not common!

In no apparent order, and probably forgetting some questions...

The island hood has to be larger at a given height to compensate for all the disturbances to the plume flow. For the specific flow rate of 90 ft/min = 90 CFM/sq. ft., the larger hood thereby requires a higher total flow rate (CFM).

MUA into existing houses, and into residences in general, require a lot of compromises that may lead in some cases to cooler air moving about than desirable, or being a tad too close to the hood, or whatever.

I am not suggesting an air curtain for any residential enterprise, unless your house is competing in the multi $10M category.

To keep my heat exchanger from freezing risk in my attic, I have two temperature probes in use, one on the copper plumbing and one under the exchanger above the diffuser. If either drops below its setting the hydronic circulation in that zone is enabled. I don't recall the exact settings, but 40F and 65F respectively are likely. Power outages are handled by a 20 kW generator in the yard. Collapse of civilization is not adequately addressed.

The hydronic loop is fully controlled by these two thresholds. When I get to shifting from passive to active, the control will be motor drive as a function of. house internal pressure differential relative to exterior pressure. This is still an undone project albeit partly constructed.

"Tricky question: does a 54" hood require more CFM than a 48" hood, over the same range, for the same cooking?" Nominally YES, because we are dealing here with residential hoods with low reservoir volume below the baffles and no control over which baffle slots are going to address a particular plume. So the baffle slot velocity has to be high over the entire baffle space.

Avoid conflicting with the NEC. It not only can have future repercussions w.r.t. insurance, but can be a real pain if easy access to panels and wiring paths is obstructed.

I think I spaced out with your kitchen MUA ducting description, but I recommend ducting that makes sense in the architecture, and if one ends up too near (whatever that actually is) to the hood, either direct the flow away from the hood, or spread it out in all directions so that the velocity of the MUA approaching the hood is low. Ideally you are replacing the kitchen air that is flowing up to the hood (or across the counter), not providing the air that is immediately flowing up to the hood, if you get my meaning. If you were, you would be in the "short-circuit" MUA mode, which doesn't do what one wants.

It is a bad idea, in my opinion, to depend on house leakage for part of the MUA. You still have to heat it, and it pulls dust and moisture where it isn't wanted.

Be sure your hydronic system boiler has its own MUA.

With respect to @User's comment: "The type of ventilation that this needs can completely empty all the air in a 4000 sf house house in 20 minutes. Island cooking needs more CFM as it is open on all sides for air currents to interfere with the flow." As most know, but just to be sure, one can't empty much of the house air with a ventilation hood blower. A couple of tenths of an inch of water column pressure loss (out of 34 ft) will shut down most hood blowers to zero flow. Compensating for flow disturbances around the hood with significantly increased flow is doomed, because outside of the hood entry aperture, the flow velocity drops like a rock. Flow would have to rise to jet engine levels. This is why a larger hood is needed for islands, and the flow rate increased proportionately to the area. It also by inference requires that there be minimal cross drafts unless the hood grows even larger to compensate.

Whew.

I concur that depending on air infiltration to provide make up air isn't the best strategy unless the leakage rate is such that you don't need to worry about make up air. That could be determined by a blower door test and it would be a really leaky house.

The required heating of make up air for occupant comfort will depend on where/how the make up air is introduced into the space and the degree of mixing. Our climate zone is certainly different from Denver's, but even in our limited period of cold weather, we haven't found the need to heat make up air. If you introduce the make up air at or near ceiling level and in reasonable proximity to the range hood, you'll minimize the need for heating for occupant comfort.

Thanks for all the thoughts, kaseki and Charles.

So, the 90 CFM/sq ft hood. And in an island it sounds like I'd want a 54x30 hood (minus a few inches of perimeter in each dimension) - so, we're looking about 1300 CFM if I'm following correctly.

Kaseki - what heat exchanger are you using with your hydronic system that doesn't have too much pressure drop? I can look up it's specs and see what type of water temp I'd need for it to work at least equal to the 10kW electric unit. I suspect, given I'm on outdoor reset with AWT at 130F and 20 degree deltaT at design condition (1 degreeF), that it might not have enough BTU output, but I should check. Also curious what control you are using? Basically sounds like it is getting treated like an indirect water heater, from a controls perspective.

I'd like to avoid a conflict with NEC, but I am truly very, very limited on options for placement of equipment, and placement of intake. I actually have to move a dryer vent just to make that work. Technically a grate below and recessed behind the back of the panel is not a code violation, but I don't want to anger an inspector.

Now, the boiler doesn't have makeup air... the 230K BTU cast iron beast of a boiler was depending on leakiness of the house, and no doubt it was sufficiently leaky. 70% of the house was either gutted or literally re-framed, so for sure it will be much tighter afterwards. To pass inspection, I'll have to put two 8" holes in the wall of the utility room. Not looking forward to introducing that cold air where the hot water is made and distributed, but again, extremely limited on options that would be code compliant.

Understood on taking care with the cross-drafts.

Charles and kaseki, understand your viewpoint on not wanting to count on the home's leakiness as part of the equation, and I will share my rationale. Feel free to straighten me out. Luckily, here in Colorado, the moisture bit is less of an issue, unless of course the home is driving humidity out, and then I could be in a situation of condensating within the insulation, though I will be using a smart vapor retarder membrane in the areas that are not getting a flash treatment. Assuming my makeup air system is tempered by an electric heater, allowing some portion of the air to be tempered by the home's radiant system will cause less of a temperature shock to the kitchen area, coupled with lower noise factors as well. Since I'm expecting some mild (say < -1 to -2Pa) depressurization in the home, there will be air coming in. In an ideal world, the makeup air system would kick in when the hood is on, and the home's pressure starts to cross some negative threshold. I think Airscape's product works this way. Let's say the house readily leaks 600 CFM at -2 Pa and the hood has 4 speeds... 300, 600, 900, 1200 CFM. Why have the makeup air system start dumping cold in one spot in the house (also think noise), unless going to the 900 or 1200 speed? I can understand the mositure and dirt concern, though in all reality, some of that leakage will be occuring already, unless the house is perfectly neutral or positively pressurized. Under said scenario, the makeup air and inefficient heater don't kick on until the hood is at level 3 or 4. As I understand, the fantech controller can be setup in this manner.

Charles - nice to hear that the need for heating may be minimal. Definitely hoping that will be case, though I feel I couldn't practically install without having some way to temper the air on those 10 degree days. At least, I think I'd hear about it from my family.

I'll have to look up my heat exchanger's parameters later. There is more of a pressure loss with a radiator type heat source than coils in the air (as in an electric dryer, for example).

The major boiler and burner manufacturers have MUA kits that surround the oil blower and feed air to the blower air intake. 6-inch duct should be overkill. This scheme keeps the cold air out of the room. However, a leaky chimney can back draft, as can the sample hole where the techs test the smoke level, depending on draft.

If you can get 600 CFM leakage at -2 Pa, then you probably don't have a back-draft problem, but this would require a very leaky house. I'm picturing a framed out window area with just a window screen. -2 Pa = - 0.008 inches, w.c.

Thanks - I was trying to avoid a lockout type situation on the boiler, mainly because if anything goes wrong with that and I'm out of town, the chances of freezing are much, much higher, and freezing a home with extensive hydronic could be spendy. However, it's worth looking at. My layout would require the duct to traverse in the panel working space, so it would be another NEC exception... working through remodels and mechanical is super ugly.

Question for you... While I am 90% confident we will go with the 48" range, there has been some talk about possibly a 36" if it made a significant difference to makeup air and ventillation. Based on what you've educated me, given the CFM need is based on hood area, and therefore it takes more heat, makeup air, and noise to cook the same 2 pots of whatever on the 48" setup versus the 36" setup (let me know if I got that wrong).

Hypothetically speaking, if I went with the wolf 36" pro island hood, which per their spec calls out 800 CFM on a 36" range, do you think that number is under spec'd? I supposed based on their comment about adding 20-25% CFM at altitude I'd be pushed into the 1200 CFM blower, as well?

First, let me emphasize that all suggested flow values from me are based on full containment of captured effluent from hot oil cooking, e.g., wok cooking or meat searing. People have managed for millennia with less performance.

Second, given that a 36-inch cooktop can be overlapped by a smaller hood than a 48-inch cooktop, then of course the flow rate can be lower, the mass airflow will be less, the heat needed for warming the air will be less, the blower will be less expensive, ...

For a 36 inch range, the hood should be at least 42 inches long. Are we still on an island?

42 x 27 inches is approximately 8 square feet. So 90 x 8 = 720 CFM actual, or 1000 CFM rated. I'd go with Wolf's 1200 CFM remote and gain some quiet operating at less than full power. The 900 CFM unit might work under some conditions. Also, use a silencer if there is room.

There may be some confusion here. The 90 ft/min value (my opinion but no one has complained yet) is intended to be actual flow velocity. To get the needed CFM that allow that flow velocity one needs a blower that can achieve that at whatever pressure losses are present. See sketch.

Without an analysis, then I suggest using a factor of 1.5 to get from require/desired air flow rate to blower zero-static-pressure rating.

Generic fan curve.

A real fan curve, but without the pressure loss imposed.

So, if one needs 1000 CFM to achieve 90 ft/min across an 11 sq. ft. hood aperture, then the blower rating should be 1500 CFM unless one knows, in particular, that the pressure loss curve of the hood's baffle array to which the duct loss and MUA uncorrected pressure loss are added allows a lower factor.

My heat exchanger was from www.heatexchangersonline.com/airtowater.htm. I think it is model HTL19x20 but haven't found a sales slip. This site may be defunct. You may have to search for heat exchangers from scratch. https://www.brazetek.com/products/details/50/15/finned-coil-water-to-air-heat-exchangers/19x20-finned-coil-water-to-air-heat-exchanger

"I was trying to avoid a lockout type situation on the boiler" By this were you implying that all your hydronic heating elements are on the same zone, or something else? The MUA heat exchanger should be on its own zone, and household wall heaters (or ceiling heaters) should be on one or more different zones. Zones can be controlled by having separate pumps, or by having separate zone valves.

Yes, understood your point. I think in our case since woking and searing are not so common, it is a worthy target, but if a good option slighly lower CFM is available, most likely it will function reasonably well, which may be where Wolf's numbers come in to the spectrum.

When I went into this, I wasn't clear if a given CFM would create a given effect on the cooking surface, generally regardless of size - but that appears not to be the case. I don't see an option of not being in the island, given the windows are in already, but we did ask the architect.

On noise - that is a very important topic.

When we started the remodel and new roof, the kitchen was planned for a future phase... and we installed a goose neck jack on the metal roof for a 10" duct. I had looked at external blowers at the time, but it seemed a bridge too far, given timing and the fact I had not picked a hood yet, let alone it wasn't on the permit.

Do you or anyone here have a sense of how noise levels would compare for an internal blower (say 900 CFM or a 1200 CFM running at 900 CFM... I'm not sure which would be less noisy) versus a roof mounted blower that is only about 2' above the ceiling, and without a silencer? I would think airflow noise would not be that bad operating at 75% in an up-n-out situation, but then there is the motor noise.

I think it will be difficult, expensive, and roof-risky to change at this point, but I did reach out to the roofer to inquire. There may be a way to come up, do a 60 degree bend, go a few feet, and another 50 degree bend to get out the roof... just adding an additional roof mounting. However, it would be pretty close to the original jack. Other option would be cutting the gooseneck to a lower height, and building a platform to attach the blower, but that sounds a bit wonky and I don't think the inspector would be happy with it not matching the mfg's instructions.

Here's what it looks like currently:

The first link didn't work, but I get the idea from the other one, and will poke around - thanks. I suspect, as you suggest, that the losses are pretty big through a heat exchanger like that.

"By this were you implying that all your hydronic heating elements are on the same zone, or something else?"

There are many zones. The lockout I was referring to was relating to if I had a fan driven makeup air for the boiler. When I spoke to the boiler plumber, he indicated that if you have fan driven makeup air for the boiler combustion, you also are required to have a lockout by which the boiler cannot operate if the fan becomes inoperable. So, if the fan goes wonky for whatever reason, the boiler is down and there's a bit higher freeze potential.

Neither MUA-for-boiler scheme I've had required a fan. The boiler just pulled air through what is at least 20 ft. of duct (some of which is now PVC).

If the attic is accessible and large enough, then one can take advantage of a "wandering" duct to fit everything in. In-line blowers are also a "thing" so one need not change the existing gooseneck. Wolf has radial in-line blowers (from Broan, probably) and Fantech has axial in-line blowers.

Fitting a Fantech silencer between hood and blower will significantly drop the noise level. (There is a noise thread here I don't have time to find the link for.) Modest bends, silencer, and longer ducting will add pressure loss, but I doubt it would be as large as the pressure loss that the baffles present.

Tables for pressure loss vs. CFM are on the heat exchanger web sites, in my experience. For my heat exchanger, the pd is about 0.3 inches at 2000 CFM.

Ahhh... thought you suggested something different previously. Nope, the Burnahm manual is quite prescriptive about the makeup air... big holes required... even bigger if ducting goes up or down.

That attic will likely never see a human after the drywall goes up. 27" of clearance at the peak, without the insulation.... likely around 18" of clearance at the high point, once the insulation is in... so no moving parts in the attic.

Hmmm. I wonder if we are writing about the same thing.

The boiler MUA is intended to keep any house pressure drop from affecting the boiler (to first order). A typical boiler oil burner (e.g., Beckett) can use a 4 inch duct and Beckett sells these. Pressure drop in the duct can be accommodated by the burner fan air adjustment. But this size is for an equally modest boiler, e.g., 100k BTUh. In the pamphlet here {https://www.beckettcorp.com/support/tech-bulletins/combustion-air-requirements-for-oil-burners/] the recommendation is a square inch per 5k BTUh. So your 250k BTUh monster would want 50 square inches or an 8-inch duct.

The hood MUA requires considerably larger ducting; very large if passive, if active (with blower), a duct size roughly the size of the hood duct. But these generalizations will be affected by what else the hood MUA might be also supplying, such as bathroom fans or other venting.

I think we are, just Burnham has some different numbers. The install manual calls for 2 ducts (one within top 12" of space, one within bottom 12" of space), with EACH sized as: 1 square inch per 4000 BTUs for all equip in the space (there is also a gas dryer). Vertical ducts, min free area 1 sq in/4000 BTU for all equipment. Horizontal ducts min free area 1 sq in/2000 BTU for all equipment. Upper and lower openings must have same free area. Also, calculate blocking effects of louvers/grilles/screens... if free area unknown, consider 60-75% free area for metal louvers.

So, yes, around 8", but you need 2. If you have any vertical component, then double both of them. Maybe more with the grate/screen to keep out animals.

Pretty crazy, eh?

Check your state's mechanical code for the make-up air required for the clothes dryer and ensure you have that amount of free vent area in addition to what you need for the other combustion devices in the same space.

Thanks, Charles - will do. The burnham install guide says to just add it to the BTUs of the boiler, in their calc. If I was to use an interlocked fan, then it would definitely be a different situation.

I think I am suggesting that a sealed duct to an oil burner (which is always blown) takes the boiler out of the MUA considerations for other combustion appliances, which would then need whatever air aperture size was described by @rossn.

So , getting back to the original topic... I am inclined to use a modified version of the Fantech MUAS system, but also want to confirm if I should rule out a fully passive system.

I've seen the Broan calculator, which (with some guessed parameters) says I'd need around (3) 10" dampers on a 1200 CFM system. This 'feels' a bit high to me, and when I spoke with Best/Broan a year or so back, they admitted it might not be so accurate.

Has there been any general rule of thumb as to opening sq inches for 1200 nominal CFM blower setups in average construction homes? I saw one posting indicating they used (2) 10" damper onto a 14" duct to address a 1000cfm deficit, and I can't imagine my deficit would be bigger than that.

Supplemental to that - In my case I'd also be looking to add a Merv 5-8 filter box to catch pollen, as it can be intense in the spring (yellow waves in the air) with all the pines we have. The 12" ducted airscape filter box I'm looking at has a pressure drop of 0.12 in at 1050 CFM, and I am guesing that will drop a fair bit with a lesser filter, but will reach out to hvacquick to confirm what those numbers are. I probably knew this at some point, but if anyone can suggest the rough means to estimate flow rate impact due to pressure drop, that would be helpful... of course getting to a true number probably is a lot more involved.

Ideally, if I decide to go passive, the system will be setup to easily convert to a fan system.

Feet per minute per square foot of filter. For lower pressure loss, use a 24 x 24 x 4-inch pleated filter.

That's very helpful. Looks like the Merv 7 comes in with the pressure drop of about 40% of the Merv 13. If their stats of Merv 13 = 0.12 in H20, then loosely might be around 0.05 presure drop.

The box I'm looking at has a V arrangment of filters, so the area is about 3.5 sq ft... but 2" thick. They also have a larger box, but not sure it will fit in my situation.

Are there many folks here reporting how many damper they installed for a given CFM hood, and what their pressure drop was? I did a search, but only found that one reference.

I think few are equipped with means of pressure drop measurement. For MUA a blower is needed that can achieve the flow rate that the kitchen hood (and any other exhausts) can reach at the calculated pressure drops of the MUA filter and heater (and ducting and intake structure). Fantech in-line axial blowers may be suitable.

Generally, dampers both at the hood and at the exterior end of the duct are desirable. For through-the-wall configurations, only one damper may be feasible. Note that the Wolf (Broan) and Abbaka roof blowers (also usable on walls) have integral dampers on the exhaust side that open as the fan spins up. Once open, dampers should have very low pressure loss. If needed, Honeywell manufactures motorized dampers.

I don't recall if @opaone has reported details of his dampers/filters, but I think his MUA is entangled in his air supply and heating systems.

ok, good note about the benefits of the damper at both ends.... will keep that in mind, noting that will add some more losses, maintenance, and length.

Odd that folks aren't checking depressurization after installing the system, to verify it is effective... especially since a manometer isn't a very expensive instrument.

On the heat exchanger... I'm now recalling that on my heating system, I am setup for 2-temp, and have a separate pump on an unused section that used to run baseboard at 180 (now gone). Ideally we were trying to bring down the overall temp of the boiler to a medium temp and add a low temp for some radiant floor downstairs, so I have to think through the long term implications of using that. If usable, it would mean all I really need is a conrol and fin-tube exchanger. I am assuming that to some extent, the heat exchanger placed just before a large diffuser may actually help the diffusion and air velocity slowing process, but maybe that thinking is not right.

I'm knee deep in tools and measuring devices, but at present only have a manometer (BAFO, I vaguely recall) that converts differential pressure to current for my future active MUA. It is installed to measure kitchen pressure vs. exterior pressure. Because the latter is very difficult ($$$) to do accurately in the presence of wind, its exterior port is physically in my heavily ventilated attic.

Having a separate manometer to measure pressure drop across my baffles would help clarify what their pressure drop is as a function of air flow, which I can measure now. Good suggestion. Keep in mind making pressure measurements implies that one can access the two measurement points.

My heat exchanger is several inches above the diffuser, so I'm not sure that the flow straightening of the exchanger is all that helpful to minimizing turbulence down the hall approaching the hood, but it may help.

As I believe I previously noted, control for the hydronic loop can be fairly simple -- at least a lot less complex than control of the MUA flow rate over the hood flow variability, along with whatever other household exhausts one deems worthy of being compensated. If one were so motivated, a proportional control of the hydronic pump could be configured to better regulate the output air temperature. Probably better with zone valves would be to duty cycle the open time vs. temperature error.

My present boiler system replacing a Weil-McLean with a batch of zone pumps is a System 2000 with a batch of gate valves, and its controller has its own opinion of how to operate. Thus, any meddling by me has to be done externally and "expressed" via the thermostat interfaces.

In my hydronic design, I won't have any zone valves, only TRVs. Probably putting a TRV sensor in the space between the heat exchanger and register would accomplish the job without another valve, and modulate the flow. I'd have to think more on this. Actually, this now has me thinking this might be accomplished only with a TRV, if I get a pump that can dead head safely.

I don't know enough about hydronic configurations that I haven't experienced to understand pluses and minuses of thermostatic radiator valves vs. on/off zone controls, so I can't comment on how well that would work. My System 2000 wants water circulating around the boiler, so there is always a circulation path if the boiler is firing, even if the zones are closed.

TRVs are amazing for zone control. If you're at 50% of design condition, they're going to flow that amount, etc. you're not shocking systems with full flow 50% of the time, but letting through the appropriate metered amount continually. Think automated flow rate management without wires, only a capillary tube and a no-power device. If you are doing anything with hydronic controls, worth looking into.

So the temperature sensing is sufficiently removed from the heating device or hot pipes that it can control room temperature? I wouldn't have guessed that from the images I looked up. Or are these proportional as you suggest, which would only work with steady state outside temperature?

Edit: I see from Wikipedia that the above questions can be answered by YES/NO, respectively, depending on the complexity of the design. I will keep them in mind.

yep. you can have an all in one or a valve with remote or wall sensor and control - they go up to 16’. have a look at this danfoss catalog. they are one of the primary manufacturers

https://assets.danfoss.com/documents/99867/AF163386458944en-010101.pdf

Side note— I know you believe in forums for these purposes. if you haven’t already been there, the ’Wall’ forum on heatinghelp.com is definitely the best hydronic resource out there - lots of knowledgable professionals and no attitude

I believe in helping a site (formerly Garden Web) that greatly aided my kitchen reno about 15 years ago. I normally don't do research here, albeit I haven't needed to. Thanks for the forum link.

And thanks for the valve information. I can see how using the TRV in concert with monoflow tees can reduce the amount of tubing needed relative to having more zones, each of which needs a return line. Optimality is probably site specific.

In my case, there aren't any monoflow tees, just manifolds. So, each room will have it's own TRV wall controller.