Poof!

Before directly commenting, I should note that my comments are generally directed a performance requirements and how to achieve them, rather than manufacturer selection, much less manufacturer pricing.

As far as I can recall, all but one Mondern Aire customer reporting here have been satisfied; the dissatisfied customer had tried to return a dented unit that had been delivered months before and not inspected. His displeasure at being unable to return the unit lead to an attempt to add his experience to every thread over the previous decade that mentioned Modern Aire. In any case, I believe Modern Aire as a company understands the functions that the hood is supposed to perform, and the methods used to do so.

I also believe Broan/Best/NuTone understand what is required, but to cover the entire cost and size range of possible hoods and blowers, they sell a lot of systems I would criticize as inadequate, or even misguided. On the other hand, they OEM Wolf blowers, one of which I have. I also have a NuTone downblast blower at least 30 years old still going strong performing secondary kitchen ventilation.

For your enlightenment, I suggest reading the first 10 or so pages of the Greenheck Guide for insight. The last place I found a copy on-line is at:

https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf

Anyway, since we are talking big bucks ventilation, it is important to keep in mind that the required make-up air (MUA) system should be expected to cost nearly as much as the hood, so this cost needs to be included in the budget.

Noise has a few factors. In my experience, and expectation from physical principles, the blower blade-tip turbulence noise dominates, followed by duct or baffle turbulence noise, depending on duct length and size. Some of these factors may not be susceptible to attenuation, depending on configuration.

For example, going directly out the wall to an external blower pretty much eliminates the duct length needed to use a silencer to attenuate blower and duct noise. An oversized blower run at part power might lead to less blower noise. And a short duct length will limit duct noise. An internal-to-the-hood blower obviously eliminates all noise reduction features that might be considered practical.

Forum member opaone is assembling a system with silencer and oversized under-driven blower. I expect it to be nearly silent, except for baffle noise. You may be able to find his comments in recent posts.

Assuming that you intend to achieve capture with a sufficient hood canopy size, and achieve containment with sufficient air velocity under the hood aperture, we could consider options for configuration changes that would provide unicorn quiet. (No one has ever reported that they are noisy, to my knowledge.)

Performance, Limited Price, Aesthetics: You can pick only two.

For low noise + good performance you need a large containment area. The effluent from cooking is quite bursty so a large containment area allows you to use lower CFM's and still exhaust most or all effluent. This is why commercial hoods are all big empty boxes and why they are quieter and do a better job than consumer hoods.

Most consumer hoods such as Modernaire have almost zero containment area and so rely on higher CFM's (greater noise) to try, and largely fail, to remove effluent.

More: https://www.gardenweb.com/discussions/5161173/hood-faq

Sellers with consumer reviews:

• build.com
• Home Depot
• appliancesconnection.com

Owners seem to like Zline hoods -- among others -- which aren't so expensive.

ok, went back to the drawing board and looking for deeper hoods (27" or greater). Several are considered outdoor hoods and one recommended 36" distance to range top surface? can outdoor hoods be used inside and installed at 30"?

I still love my GE Monogram unit. It was intalled 10 years ago. Pleanty of cfm but the features i reallly love most ... the warming shelf and heat lamp.

The hood needs to be large enough to capture by overlapping the expanding plumes as they rise up to the hood. It is not necessary for the hood to be at 30 inches; higher may provide better room for taller cooks. Commercial hoods are typically at 7 feet from the floor, but they are also generally large enough for capture. One concern is that the higher the hood entry aperture, the greater the ability of cross drafts to disturb the plume flow and cause some to miss the aperture. This is usually more of a concern for island and peninsula cooktops.

I have no sense of what makes a hood uniquely an outdoor hood.

my husband is a foot taller than me at 6' 4". A comfortable height for him would be 7' from the floor!

Normally, one stands outside the hood edge, and bends at the waist when needing to look downward into a tall pot at the back, also when reaching toward the back. If a side view of the counter, cooktop, and hood is drawn with a stick figure "tallest" person bending at the waist, the arc defined by the top of the head of the tallest cook as he bends establishes how high the hood should be if ducking is to be avoided. In my view, the lowest the hood canopy should be is determined by line-of-sight from eye height to the back burners.

When going for the 7 foot option, or for that matter any height above the cooktop, hood overlap should still be at least 10 degrees from vertical beyond the widest pan edge (or a bit more for gas). Wall location and side skirts will greatly help keep the plumes where they can be intercepted by the hood canopy. Excess volumetric flow rate (CFM) can slightly increase the effective size of the hood canopy at the cost of more blower, more noise, and more MUA.

kas

Our hood will be 30" deep so will overlap our 28" deep range by only about 2" (front of range to inside lip of hood aperture). (Typical commercial hoods are 36-40" deep for 32" deep ranges.) Our engineer @ Accurex suggested 40" above our range top (so 6'5" above the floor). She said that this should comfortably accommodate 99% of people. Lower begins to feel claustrophobic and higher reduces effluent collection.

It takes massive increases in CFM to overcome too small of an aperture for hot gaseous effluent. CFM (and containment area) is purely to eliminate positive pressure in the hood that would cause whatever is captured to roll out of the bottom. What is captured is almost purely a function of the size of the clear opening at the bottom of the hood. That said, some of the effluent we work with in our residential kitchens is not as hot as in a commercial kitchen and I do believe CFM is likely more effective than commercial hood engineers say it is but bottom line is that CFM, as @kaseki alluded to, is a poor and expensive replacement for proper hood aperture.

BTW, a pseudo exception to this is a 'front curtain MUA system'. With these the make up air is pulled down the front of the hood and then sucked in to the hood cavity. This creates and extremely high velocity of air along the front side of the hood that is better able to influence some rising effluent.

Went back to the drawing board to find a unit with a larger capture area. Came across 2 contenders: the Zephyr Cypress outdoor model with a 32" projection and the BlueStar Hampton with a 34" projection. Spoke with the big guy and he said the BS depth seems like a recipe for disaster at his height. He accuses me of trying to kill him when I leave the cabinet door above the oven open! My ceilings are only 8' high and the unit is 18" without an additional duct cover, leaving me 42" of vertical space.

Opaone, your engineer recommended 40" above the range? That's 4" higher than any hood spec I have read. (And I think I have read them all at this point!) What are you installing and how did the engineers get comfortable with that height?

I'll let opaone comment for himself, but the reason for the physics/fluid dynamics comments from me are to distinguish fundamentals from derived requirements. For capture, the fundamental issue is plume expansion, which forces smaller hood sizes to be mounted closer to the cooking zone. The commercial units account for plume expansion at greater heights by being larger.

I just spoke with the Zephyr rep about their Cypress model that has a 32" depth. She asked why that model and not a model with a standard 24" depth and an optional blower that will increase CFM's to 1300. I told her for the same reason I want it wider, I need it deeper: plume expansion! I'm pretty sure she thinks I am some eccentric kook as opposed to someone who doesn't want her kitchen to smell like a Chinese restaurant on a Saturday night. If I set it higher like Opaone, no one will be in danger of getting a concussion. Cypress has slightly less bells and whistles: 3 speeds vs 6 speeds, 1200 CFM vs 1300 CFM with optional additional blower, no remote control (who is that lazy really? ) Am I missing something here?

So now we are at 34 x 54 inches (+/- a light bar). This is 12.75 sq. ft. Actual flow should be 1150 CFM to achieve 90 ft/s velocity over the aperture. This will require a larger blower than usually supplied with or for residential hoods; perhaps 1700 CFM at zero static pressure. You may want to consider an up-blast commercial blower assembly mounted horizontally on the outside wall. These blowers usually have drives that allow different pulley ratios to achieve the desired flow rate. If large enough and "geared" down, it might also be relatively quiet. An Abbaka, Broan, or Wolf down-roof blower on the side wall will be less visually obtrusive, but these are 1500 CFM or less at zero static pressure, and generally are most tolerated with a silencer in a long-enough duct.

I must apologize for my comment about remote controls. RC makes the unit ADA compliant. My husband is going to put me in touch with one of his commercial kitchen consultants.

It'll be interesting to hear what his kitchen consultant has to say.

As @kaseki mentioned, the light bar significantly reduces the aperture. Effectively this hood is perhaps 24" deep aperture (8" light bar?). It also has almost zero containment area so bursts of effluent will roll out from under the hood.

I'd also question the baffle design. The inlet face of the baffle has a lot of flat surface. I believe a good baffle design will have more open area and often a bit of a V shape on the inlet side to make it easier for effluent to flow in to the baffle. This is just my own thought though.

Top and bottom baffles should be designed to effectively rotate the air flow through two 180-degree changes in direction while being practical to form for the price point of the hood. This rotation provides the centrifugal extraction desired, depositing grease onto the baffles where (given some slope) it will drain to the lower edges.

The baffle gaps should be approximately the baffle width so the flow will double over that at the aperture. I.e., 90 ft/min at the aperture becomes 180 ft/min in the baffle gaps, or 3 ft/s. This is about the maximum reported plume rate of rise and should keep the momentum reversal of any plume hitting the baffle surface from reflecting out of the hood. This should be enough for residential cooking. Some commercial cooking, such as charcoal grilling, will require more due to the large plume volumes emitted.

Baffle shapes such as \_/ and its inverse, overlapped top and bottom, work adequately, considering that not even commercial baffles are fully effective against the grease particulate spectrum.

And as one might surmise from opaone's comment, the goal is to have the aperture overlap the pots and pans, without depending on a light bar to provide much inward flow. Angled outward plume lines will hit the bar and compete with any (likely modest) inward air flow at the bar for their final direction, in or out.

are we talking about the Zephyr Cypress 32" x 54"?

I'm being generic in responding mainly to opaone's comment. The hood he has in mind would seem to be the Zephyr, from the context of the conversation flow, but I haven't looked at that specific hood myself to determine applicability.

OK, I looked at the Zephyr web site. Between the video and parts diagram, I would estimate that the baffle sections take up about 13 by (not over) 16 inches each, with the 16 being in the depth direction. The light bar is big, and there is also a rear cover. (The rear wall may help compensate for the rear cover's reduction of the capture aperture.) Were these significantly tilted and the baffles well up in the cavity, a single row of baffles this size would be OK.

Also, from the image in the video, I don't see the upper set of the baffle pieces being present. If so, there will be no grease extraction. This could be a hazard if there were significant duct length beyond the hood.

It seems the goals and needs of outdoor grill smoke displacement lead to different solutions than desirable for either commercial or residential indoor hoods.

My recommendation is to look at commercial hood designs and, e.g., Wolf Pro hood designs for a range of possible construction configurations that are better suited for indoor capture and containment. Maybe others here with mainstream Pro hoods can provide some image examples.

This is a wide and long

Wolf Pro Island hood.

A commercial hood might have only one row of baffles, but the capture volume below them would be much greater, and the wall angles would encourage plume momentum reflections to continue upward.

Yes, my last post regarding the light bar reducing the aperture and lack of containment area is the Zephyr Cypress.

@kaseki, here are the baffles in the Cypress (click for larger). Wide flat sections with small open gaps for effluent to try to pass through. Rather than encouraging effluent to flow in to the baffle where it will then go through the centrifugal forces to remove grease, this design creates a lot of turbulence prior to entering the baffle and has very little room for the air to move in to the baffle which is both inefficient and I'd bet will create considerable unnecessary noise. It also looks like there is nothing behind these bars but empty space so I'm not sure where grease extraction is happening? I'm guessing the design is for aesthetics rather than function.

Also, looking at this image of the Cypress, if this is 32" deep on the exterior then I'm guessing less than 20" of actual open aperture?

With a \/ \/ \/ \/ or \_/ \_/ \_/ face (rather than the |___| |___| |___| |___| face of the cypress) the effluent flows more smoothly in to the baffle where it then encounters changes in direction that remove grease.

Yes, opaone, those were my thoughts also. I think exterior hoods are intended to push smoke higher out of the way of persons lurking about the grill. I would also fear that a suitably fanatical inspector would reject this hood for interior purposes unless the installation instructions included interior use.

ok, I will move on from the Cypress. Kaseki, you said you have the Wolf. Do you like it? There is a Pro Model that is 27" as compared to the standard 24". I am going to call Wolf Technical Support to find out if the baffles on the 27" are proportionally larger than the 24" depth.

The Wolf Pro hood liner comes in 2 depths: 19" and 22". Probably safe to say that thec27c hood uses the 22" option.

Just curious, as we are currently building a house and dealing with issues picking a hood for our cooktop. But do you not also have to take into account the CFM's ratio to the total BTU outpoint of the range/cooktop and consider how the CFM's may impact your HVAC? We were cautioned that we would have to be aware of that being a potential problem. Is that incorrect?

ted: I'll get back to you on my Wolf hood measurements later today. Note that my hood is an island hood, and requires more overlap on both sides transverse to the cooking zone than a wall hood. It is important to keep in mind that cooktop overlap is just a convenience rule. The underlying function is capture of expanding plumes, and these expand at different angles vs. velocity vs. pan temperature from the pan edges (or just beyond where the gas flames emerge from under the pan and add heat to the plume). It is the locus of possible pan edges about the cooking zone that a plume expansion angle is to be measured. I think 10 degrees from vertical is representative, but this is from the largest pan (or grill or griddle) to be used for hot cooking, not the cooktop edge.

Simmering bacon and boiling water doesn't count here for determining full power hood capture and containment performance; hot plumes come from grilling, searing, and wok cooking.

Gramma T: As noted in past comments on this forum, but particularly addressed in the Greeenheck kitchen ventilation guide I linked to earlier in this thread, there are a few 'rules of thumb' that are applied to hood CFM sizing. One historical one, which I consider derivative, is total BTU output of the rangetop. A second is length of commercial hood, also derivative. The third, Greenheck's preference, and mine once I read some papers on cooking plume characteristics, is determined by the plume upward velocity and the hood size. Essentially, the goal is to have a certain minimum air velocity at the entry to the hood, depending on cooking process, to ensure that the plume stays in the hood to be transported outside. This is called 'containment.'

The other important aspect of hood function, 'capture,' is ensured by a hood large enough to overlap the rising, expanding cooking plumes.

I have recommended in this forum 90 CFM per square foot (of hood entry aperture) providing 90 ft/min velocity. That volumetric flow rate works for me, provides 180 ft/min (3 ft/s) in the baffle gaps (for large baffle area residential hoods -- the commercial hoods have smaller baffle areas but higher required baffle gap velocities due to the fluid dynamics counterpart of the Lagrange Invariant), and is essentially consistent with Greenheck's table in Figure 4 of their guide. 3 ft/s is approximately the highest plume velocity measured in certain reported commercial kitchen experiments. Greenheck goes further to ever higher velocities, but the relevant cooking devices, such as char broilers, are not representative of residential kitchen equipment.

In addition to having sufficient flow rate, it is necessary to have low differential house pressure (review MUA threads here). For all but very modest hood flow rates, make-up air is required and this is another HVAC system and associated bag of worms.

kaseki, I'm throwing a wrench into the works. I will not have a separate MUA system. My house is 80+ years old and leaks like a sieve already. Don't shoot the messenger.

To answer an earlier question, my Wolf hood has an interior entrance aperture area of 26 x 61 inches, or 11 square feet. Wolf wall hoods are not quite as deep. According to my Wolf info, somewhat old, the Wolf Pro wall hood is available in 27 inches total depth. I don't know where the front edge of the aperture is from the wall, but I would guess it is at 22 inches. (My light bar is about 5 inches.) The inserts are apparently smaller. My hood was actually made by Independent for Wolf, so acquiring modern data is advisable.

Depending on various details of burner layout, air flow, side barriers, hood height, etc., 22 inches may be sufficient to ensure capture for all likely cooking conditions.

In the interest of being informative, let me provide some perspective on MUA.

a) There is always MUA. Every cubic foot of air that flows out of the kitchen through the hood is replaced. If the house restricts the MUA, so also is the hood's flow rate restricted.

b) Deliberate MUA helps keep the hood flow rate where one wants it.

c) With less MUA, not only is the hood restricted, but the house pressure falls relative to the outside. This can cause undesirable effects:

• Combustion appliances can be back-drafted, pulling carbon monoxide into the house
• Moisture can be pulled into the house walls leading to mold
• Dust and fiber glass particles in the walls can be pulled into the house.

d) In many (now maybe most) municipalities, or at the state level, there is a value of vent hood nominal flow rate that if surpassed requires some sort of MUA system, even rudimentary. Some municipalities will require it to be heated (Minnesota was it?). This may not be enforceable if one doesn't have a building permit that requires inspection. Or, for very leaky houses, the Code Enforcement Officer may allow no MUA system.

The safety issue is the big one for inspectors. If you have no combustion appliances, or they have their own MUA and can't easily be back-drafted, the inspector may let you off the MUA hook.

My oil burner furnace is my only combustion appliance. It has a sealed MUA duct, sealed burner, and a sealed exhaust duct. Back-drafting is not a risk. My MUA system is intended to heat the make-up air in winter and allow the hood (shown earlier in this thread), as well as an auxiliary kitchen vent above my wall ovens, to operate at the restriction levels induced by their respective baffles and ducts.

Most codes require MUA for any exhausting appliance over 600 CFM. However, that was written for a fairly leaky house of ACH50 = 4.0 or greater. Most newer houses in colder climates are < 2.0 and many around 1.0 or below which should have powered MUA for anything over about 200 CFM.

As @kaseki pointed out, MUA is important regardless of code. Current U.S. code allows for quite poor indoor air quality which leads to a lot of health problems for people in the U.S. We are about 20 years behind Europe on IAQ.

Not having adequate MUA also leads to poor hood performance. An 800 CFM hood should function at 800 CFM with proper MUA but if having to suck air through wall cracks may only exhaust 200 CFM.

Understood. Architect (and architect husband) said that it will not be required. I am due to meet with him again next week or the week after. If we are opening most of the space there should be a way to put in a simple MUA. We live in the Northeast (NYC suburb), A/C is retrofitted into most of the homes original closet space. Can an MUA system be as simple as a register the motorized damper and air intake? Husband is worried that if the air is not conditioned (hot or cold) it will mess up the balance. P.S. IMHO it is already messed up considering we only have one zone and steam heat.

BTW, something that we considered prior to our Accurex was using a Wolf liner but installing it about 10" higher up in the hood surround so effectively creating some containment area and a larger capture aperture since the light bar would no longer be at the opening. We chose not to do this because it would either have left the controls up higher in the hood and somewhat difficult to reach or required a bunch of work to place the controls somewhere easier to reach.

The Accurex solution was a bit more expensive but avoided these problems and should result in a much quieter hood. Later on our AV/HA contractor said that they could easily have tied the hood control in to our automation system to control it from the kitchen control panel.

Something to consider.

tedb1973 wrote: Can an MUA system be as simple as a register the motorized damper and air intake?

Yes. It can also use a non motorized damper under some conditions, if you don't mind a bit of flapping in the wind.

If a heat exchanger is used for heating, it may cause some pressure loss. Electric coil heating used in many commercial MUA assemblies probably has the lowest pressure loss.

If you filter the air with a furnace filter like assembly, there will also be some pressure loss. These pressure losses will reduce the MUA flow, but perhaps not significantly enough to keep you from using either. (They can, however, easily violate the 0.03 in H2O water column pressure limit of back-drafting gas appliances.) Note that some screening will be desirable in any case. If the pressure loss needs to be made up, then the complexity of a blower powered MUA becomes necessary. This all depends on how leaky your house is.

A slightly more complex system than the bare damper and intake (but just barely) is to insert the MUA into a room (entry, mud room, basement) that is heated under control of its own thermostat and also connected, air-path-wise, to the kitchen. The heater has to be more powerful than the room would normally require. See graph (click for magnification).

In any case, insertion of MUA into the kitchen has to be done in a manner that avoids causing cross drafts at the cooktop. A ceiling diffuser far away (down a hall, say) or aimed away from the hood, or floor insertion aimed away from the hood should work. Note that if the toe kick area is used, it needs to be a lot of toe kick area to avoid turbulence at the hood. Try to have MUA flow where it reaches the kitchen exit from at least the same area as the hood.

I have a 2 x 2 ft heat exchanger feeding a 3 x 3 ft Hart & Cooley diffuser at the opposite end of a hall connected to the kitchen. My goal is quasi-laminar flow when the air reaches the kitchen. The hall sectional area (H x W) is 24 square feet, so 1000 CFM implies a 40 ft/min air flow. This seems to be OK in my case, perhaps because it is spreading into a 216 square foot sectional area. A nearby Mitsubishi A/C head, however, can direct air toward the hood and will cause some deviation of the cooking plumes if allowed to do so.

Here are some pictures to put things into perspective. Half of the kitchen is under the master bedroom, can't vent vertically. The other half of the kitchen sits under its own roofline, previous kitchen redesign vaulted this space. This would have been the original maid's room (with full bath, now just a powder room). We plan on keeping the vault, but adding a soffit to tie the ceiling line between the two areas (red line). Door is going to be removed. Range and hood will straddle the area where the door and wall ovens currently are. Hood will vent straight out the back. The two vents are the current A/C registers. I am trying not to disturb the A/C. Do you think a small MUA system can be put into the soffit? I have no concept of how much room it needs.

Is there a basement? How cold does it get in the winter? Can you penetrate the roof into the vaulted area? Would a diffuser there be perceived as too ugly?

Behind the wall where the two registers are is what -- the master bedroom? How are the registers in that wall fed air?

New range area: Can some of the cabinetry around it sacrifice some space so that MUA can be brought in there (either from outside or via a basement) and projected across the kitchen floor?

A passive (no blower MUA) just needs a duct about the same size as the one servicing the hood, but depending on location this ducted air needs to be spread out into a larger area.

Below the kitchen window is the laundry room with a light well. The solid brick wall is my recently renovated master bath (not touching that LOL). Then there is the roofline of the maid's room. Roof is slate, which is fun to deal with. Only my neighbor would see the diffuser. How big is a diffuser? Would my regular HVAC service company be the ones to work on something like this?

A diffuser is like a register but with larger adjustable blades. If you use one, it would be visible inside, not outside. Outside would just need a duct cap.

Your HVAC company should be advising you of your MUA options.

Knowing as little as I do about your house's architecture, I would at this point think about pulling the MUA into the laundry room, heating it there or not, and putting it through the floor into the kitchen via some of the cabinet bases.

I will call them tomorrow.

And the saga continues....HVAC man came by. looked all around, house is not tight but current state code is requiring MUA above 400 or 600 CFM, but enforcement is varying town by town. The town 3 miles away is rejecting permits without MUA. My town is not. He said given location of furnace and if I absolutely promised to crack a window, he'd be ok with no MUA. If the plans get rejected because of a lack of MUA, a simple unconditioned system could be put in through the crawl space at around $1800-$2500. That is of course if I get rid of the infestation of the biggest crickets he has ever seen in his life that are presently residing the crawl space. Still haven't connected with Kitchen consultant.

@tedb1973 I realize this as ancient thread but curious to know what you ended up with?

I put in 60" Best Classico model with IQ12 internal blower over 48" BlueStar range top. Back vented, installation has its issues (it is cold b/c vent opening is on extrrnal wall, no room for dampers), but it works like it should. I recommend it.

The cap on the outside should be configured for a damper. I have a blower cap combo with a damper that opens with blower actuation, but I don't know if the same design will work with an internal [to the hood] blower.

too dark outside to take a picture, but there is a damper I believe...a flap that opens when the hood is turned on and then there is a housing around it. Problem is that it does not not shut vacuum tight so if you put your hand up to the vent grates you can feel cold air on a cold winter day. Also if the wind comes down the side of the house, it rattles that outside vent cover and the damper rattles. Supposedly that might be fixed with a tighter spring.

on second thought it might just be a vent cap with a flappy thing that opens when the hood is turned on.

That's a common problem w/ short direct runs like that.

Something that can happen is wind flows across near ground level and when it hits your wall it flows upward in to the housing and lifts the flap. If that's what's happening there are few ways to deal with it. One is to deflect the wind from doing that either with a ground level berm that forces the wind to flow above the wall cap and another is a deflector below the wall cap.

If you have sheet metal skills available then you can make a new flapper that pushes closed when there is an updraft of wind like that.

Thanks!  We will look into it.  Problem is much like when a toddler first discovers a mirror.  They look in the back to see the other person and there is no one there.  When the wind blows and we go outside to see what is happening, everything goes still.

In other words, an angled tang on the flapper that produces closing force when subjected to rising air flow?