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hood questions 101--not cfm or mua

Posted by needinfo1 (My Page) on
Sat, Feb 2, 13 at 13:33

I'll preface this by saying I really don't like hoods. But, I need to buy one. We just took out an old downdraft Jenn-Air and need a hood to go over our new all gas 30" Wolf. Honestly, we lived with this system for twenty years, so any configuration I go with will be an improvement. I am not looking for perfection in ventilation.

I've been reading here and get the CFM and MUA aspects and vented vs. non-vented issues. I have questions about brands and mesh filters vs. baffles vs. whatever the Vent-a-Hood type filter is called.

We have size and space and configuration constraints, and to me most hoods are pretty unattractive. We will be going straight up to our 9' ceiling where the venting will have to make a 90 degree turn and then run out between the joists for about five feet before it reaches the outside wall.

My house is from 1916, and my kitchen is designed more to have the look and feel of a 1920s to 1930s kitchen. I want something rather simple in appearance but yet with some style. I have been looking and looking and haven't found many hoods that appeal to me (especially at a price I want to pay). The Bertazzoni Heritage looks kind of interesting. http://us.bertazzoni.com/heritage-series/ventilations/30-canopy-and-base-hood

But, this has mesh filters. So, my first question is about filters. I think I have read here that mesh filters are no good. Am I right? What type of filters should I really be looking for? What is the concensus here about Vent-a Hood with its different type of filters?

My next question is about manufacturers. Who should I seriously be looking at?

And, is there any place Modernaire sells mistakes or returned orders like Rangecraft does?

I'd appreciate some information from the deep knowledge bank here.


Follow-Up Postings:

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RE: hood questions 101--not cfm or mua

I got a Kobe hood with baffle filters. It's relatively quiet and easy to clean. They have a lot of styles. One advantage of a Kobe is that it can be adapted to different sized vents. I ordered mine from ventingdirect.com because there was no Kobe dealer anywhere near my city.

Whatever hood you get, make sure you open it and check for dents before you accept it. More than one person has found later, when they go to install, that the hood was damaged in shipping.

I don't know if they are more money, but would wooden surround over a fan insert suit your kitchen better?


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RE: hood questions 101--not cfm or mua

"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.

kas


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RE: hood questions 101--not cfm or mua

Ginny--Thanks for the info about the Kobe. I'll check into that. Because of the strange configuration we are dealing with, we are unable to do the wooden frame for a hood.

Kaseki--So, perhaps the appropriate thing to say is that mesh filters are not as effective as baffles but can work if kept clean? Noise is a concern of mine. I don't want something that sounds like a jet on a runway (exaggerating a bit here). Perhaps baffles are the ideal compromise.

I know VAH markets itself as much more efficient--e.g. their 300 CFM will actually perform the same as someone else's 450CFM. Are people here in agreement with that statement? I guess if that were true, I might be willing to put up with a bit of extra noise and cleaning hassle.

Thanks to both of you.


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RE: hood questions 101--not cfm or mua

So . . . maybe another approach? I'm not saying one cannot make do without baffles (and the standard design capture area), because people make do with all sorts of arrangements, but if you really don't like the appearance of most hoods, but you want a well-functioning ventilation system, have you considered hiding the hood? Apart from all sorts of OTS covers, you could make something, or have something made, that's more in concert with the rest of your kitchen, if that's important to you.


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RE: hood questions 101--not cfm or mua

I had a Tradewind hood installed last summer/fall, and so far we love it. It's made by Universal Metal Industries, and I bought it on a recommendation by Trailrunner, who cooks a ton. She did not steer me wrong. I ordered by phone and the people were down-to-earth and helpful, helping me figure out which parts to buy; I didn't want to pay the $$ for a Modern-Aire and think this one is a good substitute. I need to clean the baffles (dw) now; boy, does that thing pick up the oil. I'm very impressed.


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RE: hood questions 101--not cfm or mua

Thanks sjerin--

I am going to look into this brand. Who did you buy from?


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RE: hood questions 101--not cfm or mua

The OP wrote:

"Kaseki--So, perhaps the appropriate thing to say is that mesh filters are not as effective as baffles but can work if kept clean? Noise is a concern of mine. I don't want something that sounds like a jet on a runway (exaggerating a bit here). Perhaps baffles are the ideal compromise. "

I thought what I said was they can be equal if clean, without explicitly noting that clean is a condition that may be brief. For the same flow rate, I would expect mesh filters to generate a bit more hiss. Fan blade turbulence noise will depend on the fan and other factors, but whatever acoustic level the tip noise is, I would expect little perceived difference to the cook between baffles and mesh filters, everything else being equal.

"I know VAH markets itself as much more efficient--e.g. their 300 CFM will actually perform the same as someone else's 450CFM. Are people here in agreement with that statement? I guess if that were true, I might be willing to put up with a bit of extra noise and cleaning hassle. "

This has been commented on here in many threads, including a recent one by me. It is unlikely the motors are more efficient (air moved per hour per kw-hr used). Grease collection fraction over the particle spectrum has never been published, to my knowledge, so comparative collection efficiency is unknown. The claim of being equivalent to a 50% greater cfm standard configuration is, in my view, likely to be a comparison of "apples to oranges."

Normally, fans are specified as having a particular flow rate at zero static pressure, and as the pressure difference across them increases, the flow decreases. The relationship is typically plotted in a "fan curve." Respectable fan manufacturers will publish the curves for their fans. Broan has fan curves on their web site. For other examples, see Rotron and Fantech (published as tables).

What I believe VAH are saying is that in their fan housing, their fan moves X cfm, but if it were in the open as other fans are rated it would move 1.5X cfm. Unfortunately, that is not the whole story. There are other pressure losses in a system, such as duct friction loss, turning loss, transition loss, filter loss, and, sometimes the largest, the lack of adequate make-up air loss (the house pressure goes negative). So, without a fan curve one cannot determine how much lower the cfm will be for a VAH in situ. Not that the situation is all that much better for the fans with fan curves, because the hood and baffle losses have to be guessed at for most hoods (commercial being an exception). And house pressure has to be estimated depending on what MUA system, if any, will be in use.

As a gross rule of thumb, I assume that baffle hood systems normally configured without more than 0.03 inches of MUA loss will meet the VAH factor; that is, the actual cfm will be 2/3 the zero static pressure cfm rating of the fan. (Note that more negative house pressure will backdraft some combustion appliances and should be avoided.)

kas


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RE: hood questions 101--not cfm or mua

Wow! Kas, you are the engineering genius here!


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RE: hood questions 101--not cfm or mua

I would go with baffles and an external exhauster (one mounted outside. These are very quiet - and with a variable speed fan, you can dial in any amount of ventilation you desire.

I would stay away from the aluminum mesh filters - really old school and a mess to clean.


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RE: hood questions 101--not cfm or mua

I ordered straight from Tradewind and had it sent to my contractor.


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