If you do a lot of high-heat wok frying or other high-heat cooking, you may need to bite the bullet, replace your 6" ducting, and go for the 600 cfm Vent-A-Hood. On the other hand, if most of your cooking is simply done in a sauté pan or in sauce pots with bubbling liquids, then the 300 cfm model should prove entirely adequate.

I have a 600 cfm Vent-A-Hood over a 36" cooktop. I don't do a lot of wok cooking, but I do a lot of pan-searing, sauté work and reductions. About 98% of the time I operate the range hood on the lowest SensaSource setting (which I think is around 200 cfm), and it works very effectively. I'd estimate that I operate the range hood at 600 cfm less than 1% of the time, usually only when I'm not paying enough attention, and accidently overheat oil in a pan (a smokey mis-adventure), before I begin cooking.

If you have the available space, you can increase the capture ability of your range hood by choosing a model that is 27" deep and/or wider than your 30" range.

If replacing the ducting isn't a possibility, then go with a 300 cfm model. Installing a 600 cfm model with inadequate ducting won't make it vent any more effectively, but it will make it noisier.

You can find 600 CFM hoods that only require 6" ducting. My DCS Eurohood is one, but I think the current model requires a larger duct. Check out Zephyr, Kobe and some other brands - I know I've seen them.

We have a 27" deep 300 CFM VAH. It does a fine job of capturing the smoke from full blast frying on the 15,000 BTU front burner of our Lacanche range. The hood overhangs the range by 3" on that side, which helps. (The 30" hood is installed off center above the 27" range for just that reason.)

300 isn't enough. Do what you have to to get more. Also, don't scrimp on the capture area. That's as important -- I think more important -- than CFM but most folks don't pay much attention to it. "Pretty" is all well and good, but that vent has a job to do and the capture area is a huge component of how well it's going to work.

I have a Futuro that has a 6" vent with 900 CFM's. Has only been installed a short time but we have used it on high for bacon cooking and couple of other strong smelling items(brussel sprouts) and it is doing an excellant job.

And we love the look of it.

Even if a hi capacity exhaust system is designed to work in a 6 inch duct, it is likely to make more noise from the sound of the air rushing through the duct than a system with a larger duct. If noise is an issue for you, you should take that into account.

Also, it is possible to install too high a capacity exhaust system. In that case you will create a negative air pressure situation in you kitchen, and need to open a window to compensate for that. In restaurants, they sometimes install a separate air intake system to deal with that. That's almost never done in homes. But you should expect to have to open a window in your kitchen if you're running a high capacity exhaust at full strength. That depends on how much heat and smoke you expect to generate.

I have a 300 CFM VAH and it's enough for me but I just have a Wolf cooktop - not a super duper Bluestar. I don't do much of any greasy cooking. I sear fish sometimes but that's not the kind of thing where grease is flying everywhere. The 300 CFM sucks up moisture, smoke and odors which is pretty much what I produce. Mine goes immediately straight out so I imagine that helps the effectiveness plus its in kind of an enclosed section of cabinetry so that probably helps too. I was all set to get a 600 CFM but in my case code required a make-up air system for anything over 300 CFM - which was $4K - you can't just open a window in Minnesota in the winter. Ventilation wasn't THAT important to me. In retrospect I think I made the right decision since the fan noise drives me nuts - I use it only when I think it's really necessary - which isn't that often.

Its not going to be enough!!I had one 300 CFM and didn't do the job. Then I bought one 860 CFM (SV168F-30 Spagna Vetro).This thing sucks like crazy!!I bought it from Vancouver(kitchenhoods.ca). 36" with 6" duct!!
Works perfect!

First of all, IÂd like to point out that thereÂs a difference between the real CFM and the "chinese CFM". The difference is, that a REAL 300-450 CFM hood, thatÂs made in Europe or the US (please donÂt confuse with "Italian style" or "Japanese design"), even with a 6" duct - would do the job (unless you have a grill).

On the other hand, there is a lot of Chinese-made junk floating around (such as Spagna Vetro, Euro-Kitchen, Cavaliere, Veneto, Kobe, Lux-Air, and many more to come), which advertise 900 CFM - but in real life, thatÂs nothing but false specifications, no matter what size duct you have.

That includes the quality of stainless steel, components, UL approvals, and hidden origin of manufacture. We have tested (with a 6" floating-ball test) the Euro-Kitchen (formerly Spagna), and the result was 342 CFM on the highest speed, at zero static pressure.

I fell in love with the Zephyr Tamburo(400 CFM) and called Caldera to find out how many CFMs I would need for the 30" gas cooktop. Al, one of the owners, told me that 400 would be plenty and that he has that same CFM in his own home. I think if you are not going to do a lot of high-heat frying or have all the burners on your big stove at one time, 300 might be ok.

I dunno. Hard for me to imagine getting a stove with 22K BTU and NOT cranking it up. Why not save the money then? I think 300 is not enough for someone wanting to maximize the use of his BS RNB.

300 is not enough, that's all there is too it.

No, and you'll have to open up that 6" to at least an 8" diameter hole to get more cfm through it or you're going to get a lot of unwanted noise.

You need 1 CFM per 100 BTU. So, if you have a single burner on high at 22,000 BTU's, you'll need 220 CFM. It's additive, so the more burners you have going at once, the more ventilation you'll need. Have 3 burners going at 20,000 + 12,000+ 9,000? This is now 41,000 BTUs and you'll need 410 CFM to properly vent your kitchen. See how this works? So, just do the math and don't skimp on ventilation now, because your house will stink forever if you get this wrong. Cheers....AA

I bought a 36" Blue star four burner with char grill, last year. Instead of buying one of the name brand vent hoods I purchased a commercial hood and remote blower from a restaurant supply house in my (Brooklyn, NY) area. The hood is 48"W/30"D/20"H. I have an 8" duct with a large commercial blower meant for a 10" or larger duct. I wanted a 10" duct but needed to vent from the side of the hood and a 10" would have been too large to fit between the hood and slanted baffle filters. If I were able to vent from the back or top I could have gone larger. This set up draws any, and all smoke that I have been able to generate from searing, frying, and grilling. I believe that the large capture area of the hood is the major factor in controlling the smoke. With the 8" duct and the large blower the down side is noise. I had a hood with a remote 450CFM blower on my previous range that just matched the range dimensions and it was not able to keep up with the smoke when searing or frying. If the hood had been larger the 450 blower may have been able to keep the smoke at a more tolerable level. IÂm quite satisfied with my range and venting system, and I think for the average home cook it's more than sufficient.
Frank.

So many variables, so little information. Every time I read through these posts on ventilation it seems people are talking past each other or at least past me and my meager fund of knowledge. Gas cooking from what I can gather is a completely different equation from electric or induction. Island venting varies from wall mounted venting. Venting directly to the outside from wall mounted also differs from venting through the roof or along a long run to an outside wall if the kitchen is configured is such a way that there is no way possible to place the cooktop on an outside wall.

I don't want to hijack here but is there truly any succinct source for information that will enable a consumer to sort through all these variables and understand all of the above not to mention internal vs. remote fans (I think I understand the rudiments of baffles vs. mesh). Makes me long for the days of middle school algebra. I need some way to categorize and sort information and product websites seem information deficient or geared to ventilation professionals. Is it just me and it's too late at night for me to think straight? Help.

There's a faq on this forum that has a post on ventilation - I haven't looked at it in a while so I'm not sure how comprehensive it is. There are a number of variables and different people have different biases.

By the way, I strongly disagree with the statement that gas is different from electric or induction. It's WHAT you cook, not what fuel you cook it with. A properly functioning gas hood does not produce CO so those who tell you that you need to vent dangerous fumes from a gas cooktop are wrong.

Also there is a rule of thumb for computing the number of CFMs you need based on the maximum number of BTUs your cooktop can produce. That's fine if you run everything on maximum all the time but often can be overkill. There was an article posted here a while ago about how range/hood manufacturers were overselling hoods.

Unless you have a grill, 600 CFMs will be adequate for most applications. It's true that the length of the duct will reduce CFMs, but unless you've got an exceptionally long run with many turns, it shouldn't affect you too much.

Capture area of the hood is important - the deeper the hood the better.

For theory (mostly applied to commercial kitchens), review the support material at Greenheck.com and CaptiveAire.com. For theory and measurements, find the two Thermal Plume papers by Kosonen Risto, Koskela Hannu, and Saarinen Pekka. For flow around hoods, see the 2003 HVAC Applications ASHRAE Handbook.

Because it is easier for fans to make pressure than vacuum, properly sized systems with the fan in the hood can _tolerate_ smaller ducts than those with the fan in the roof. However, undersized ducts fed from the hood are undesirable for several reasons, such as efficiency and noise.

There is a difference between gas cooking and induction cooking, and it has to do with how they work and the energy expended to do the work. The afore mentioned Thermal Plume papers are particularly useful in understanding this. Also please note that the Wolf sizing charts for exhaust fans have lower required cfm values listed for induction systems.

kas

Thank you weissman and kaseki. This will be my homework for tonight.