Hood - baffles or mesh (or Ventahood)?

Caliente63February 27, 2013

For a long time, we had imagined that we "must have" baffles in our new range hood. In part, this is based on years of experience of oil dripping from mesh filters on every hood we have had so far. (My DW points out that the dripping oil is perhaps more of a reflection of insufficiently frequent cleaning than an inevitable characteristic.)

I happened across a comment in these forums (probably from Kas) that said baffles require a minimum air flow to work properly. Does this mean that mesh filters may actually be a better choice for people who don't always run their hoods at full speed? Do Ventahood's blowers (which eliminate the need for filters, if I understand correctly) represent a valid solution?

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IMO if you are going with a 400 cfm or lower blower you want mesh filters if higher you want baffles.

I really don't like VAH. In general beware products that are marketed as "magic" or "miracle".

Pointless to buy a variable speed blower with 500 plus cfm and choose mesh filters to optimize performance at 100 cfm because you don't always run hood at full speed.

I don't think anyone who has baffle filters(generally more powerful blowers) runs their hood at full speed all the time.

    Bookmark   February 27, 2013 at 3:26PM
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I have a Venta Hood model ZTH 36 inch width. The specs say that it has 600cfm and because of its "magic lung" design it can handle professional cooking equipment that calls for 900cfm venting. I have my VentaHood paired with a Dacor gas 36 inch cooktop (which I'm sure doesn't count as professional style cooking equipment although to me it is pretty powerful).
I am extremely happy with the performance of the VentaHood. I love the way it senses the amount of heat and kicks the fan into a higher gear as needed.
I am amazed every time I clean the hood how much grease it has collected. I previously had external venting via an over the range microwave and now I can literally see why my previous cabinets always had got a film of grease on them. That microwave just didn't suck like this VentaHood does.

    Bookmark   February 27, 2013 at 4:48PM
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badgergal: how many speeds does your VAH have? Does it have one motor, or two?

    Bookmark   February 27, 2013 at 4:58PM
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I have a 4+ yr old 600 cfm Ventahood and it has 3 speeds.

BTW, I totally discount the hype. My range (36" DCS AG, 6 burners) recommended 600 cfm, and my code-compliant installation used 600 cfm criteria. If you need 900 cfm, get a 900 cfm vent, whatever the brand.

    Bookmark   February 27, 2013 at 5:12PM
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Caliente63, my VentaHood has two motors each operated by its own switch. There is a blower on the left that has a single speed. The blower on the right can be set for a low or high speed. It also has a sensor so if it is on low and it senses the cooking temperature getting too high it automatically shifts the fan to high and then shifts it back to low when the heat lowers.
So with there being 1 speed on one blower and 2 speeds on the other I guess you could say that there are 3 speeds.
It also has 4 halogen lights that can be set to low or high. At the high setting they really light up the cooktop and even some of the surrounding area.This also beats the extremely poor light that was provided by my previous OTR microwave/vent.

    Bookmark   February 27, 2013 at 6:29PM
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I don't think I said that exactly, but it is true that if one wants grease particles to be thrown out of an air stream, there is a certain rotational velocity (perhaps inversely proportional to particle size) that is needed. Generally, if one is generating a lot of greasy effluent, the fan will be on high, and otherwise when conditions are appropriate for low speed, there may not be much grease to remove.

Neither baffles nor meshes are efficient at capturing the smaller end of the grease particulate spectrum, but those particles tend not to condense out of the air and onto the ducts, so they are released into the air outside. This is also true for commercial setups. Where capture of a wide portion of the spectrum is required, staged filters of different types are used. This is why an effective recirculating filter would take up a lot of ceiling space.


    Bookmark   February 27, 2013 at 6:41PM
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Do you have any thoughts on the differences (if any) between mesh and baffles? Mesh seems to provide a more tortuous path than baffles.

I also wonder about the effect of the surface area in contact with the air stream. It seems like mesh would have a greater surface area than baffles.

The situation I am concerned with is where we are generating a modest amount of greasy effluent. For example, softening onions in a little oil. We would not turn the hood up full in that situation, but there is still some oil being thrown into the air, both as droplets and as vapor. For each time we do something aggressive like stir frying, we probably do something moderate like soften onions ten times. We'd prefer not to suck too much cold air into the house on such occasions.

    Bookmark   February 27, 2013 at 7:59PM
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Baffles don't directly depend on surface area, as I understand their capture process. However, if you were to calculate the total baffle surface area (at least of my Wolf/Independent hood), it would greatly exceed the area of a mesh filling that same space (based on my memory of the mesh filter in my former Litton CookCenter). Due to its design, the baffle surface area is greater than the aperture area. Baffles are also more tortuous unless the mesh is several layers.

A mesh filter, particularly with a little grease and a little lint, should be able to filter fairly effectively at low air velocity rates. This won't last long, though, if it starts clogging.

As I have noted elsewhere, baffles continue to work when greasy, meshes increase pressure loss and thus ventilation rate when dirty. At low speeds and for kitchens where avoiding MUA systems has led to the choice of low cfm and thus low velocity, meshes kept fairly clean should be fine. Unfortunately, they tend to be used without any capture volume below them, which can degrade capture performance.


    Bookmark   February 28, 2013 at 11:57AM
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Kas--if you don't mind, I'm going to quote you from another thread on this issue that I saved in my clippings.

"Mesh filters are no good" is too strong of an interpretation of the issues. There are some advantages to baffle filters, but both types can remove part of the grease particle spectrum. The biggest advantages of baffles over meshes is that their effectiveness is unaffected by getting dirty, and when dirty, they don't increase the pressure drop across them, which would move the operating point up and left on the fan curve to lower cfm.
There is another aspect of mesh filters, and that is that they are often designed to fit flush with the aperture opening of the hood. This can cause reduced capture. Mesh filters may have higher noise than baffles for the same air velocity at the aperture.

Vent-a-Hood uses the same principle as baffles, but via a different process. In a normal baffle hood with sufficient air velocity, the reversal of direction passing through the baffles centrifugally throws the grease particles (at least a good portion of them) against the baffles where the grease collects. The VAH uses the fan itself to throw grease particles against the fan housing where much of the grease particulate collects.

Complaints about VAH on this forum have related to sound level, inconvenience in cleaning, and at least one case where cleaning removed the paint from the housing. I believe Clinresga has provided some measured results on noise in earlier threads, which you can hunt down using a search tool.


    Bookmark   February 28, 2013 at 12:57PM
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Couldn't have said it better myself. :)


    Bookmark   March 2, 2013 at 11:29AM
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Do mesh and baffle filters have different noise characteristics? I'm going to have an external blower so I think my main source of noise at moderate speeds is going to be the air rushing over the filter. Does anyone who's experienced both have an opinion?

FWIW, the two hoods I'm considering are a Best with mesh filters and an 8" duct vs. a ModernAire with baffle filters and a 10" duct. Otherwise they're very similar except the ModernAire's capture area is maybe 1" deeper. Both would have an external blower and perhaps a silencer. I think I can get the Best hood quite a bit cheaper, but if it's likely to be significantly louder I can splurge and get the ModernAire. Any suggestions?


    Bookmark   March 4, 2013 at 8:38PM
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I can only guess on this one because a true comparison would require both to be the same size and have the same achieved air flow rate. I would not expect anyone to have such a setup that could be compared.

The baffle noise will be due to turbulence from air passing over the sharp edges of the baffle sheet metal.

The mesh noise will be due to turbulence from air passing over the edges of the mesh holes.

Although baffles have more metal surface than meshes filling the same area, I would argue that baffles have less edge length. This suggests that the mesh filters would generate more turbulence and thus be noisier. However, the size of the turbulence cells could be different in each case, and the sound frequency spectrum for one might be different than the other, leading to different perceptions of the noise relative to the actual achieved acoustic power.

So, we are faced with a lot of qualitative fluid dynamics phenomena that don't lead to an obvious conclusion, so intuition prevails. In my estimation baffles will be no more noisy than meshes for the same air flow rate. I would also estimate that at moderate flow rates where the mesh induced noise isn't partly ultrasonic, the mesh noise will be louder.

Also, relative to the italics above, equal fans do not yield equal flow rates, even with perfect MUA control. The losses in ducts of different diameter are not equal, and meshes will cause greater pressure loss, even when clean, than baffles for the same actual aperture area. (And most mesh filters do not cover as much area under their hood's boundaries as baffles usually do for the same hood boundaries.) So the flow rate achieved with meshes may be lower, but at the same time the air velocity at the mesh may be higher, and hence more noise is generated per unit area for less area. This is a non-trivial condition for which to have to estimate relative noise.


    Bookmark   March 5, 2013 at 11:33AM
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Thanks for the detailed answer, kas!

My intuition about noise corresponds with what (I think) you said: for equal air flows, a mesh filter would be a bit louder -- at least at mid / high frequencies -- from the air being sucked through the small holes in the mesh. (I should be safe assuming equal flow rate at the filter just because I'll have a variable speed controller on the fan, so I can adjust it to whatever flow rate I need for good capture.)

I'm leaning toward getting the ModernAire hood with baffle filters, plus a silencer if I can squeeze it into the available space between the ceiling joists and the flat roof just above them. I sent an email to ModernAire asking for the name of a local dealer so I can get an exact quote, since their web site is pretty useless in that department.


    Bookmark   March 5, 2013 at 1:02PM
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