It is normal to go from rectangular to round. The part is called an adaptor. It is widely available.

-david

Not optimal ducting: your rectangular is about the equivalent of 6'' duct. But, better than nothing. Davidro is right, should be possible to transition from one to the other pretty easily.

But...baffles vs oil can? No brainer. Baffles. The whole oil can concept leaves me totally cold. Looks goofy. Don't want to empty a can full of nasty grease. Baffles? They look cool. They work. They are easy to clean (throw them in DW). And, there's a reason that every restaurant in the world uses baffles, not oil cans.

So, if I go with the Kobe Ch191 with baffles and a 6 inch round duct it shouldn't be a problem for install?

Clinresga- what did you mean about not optimal ducting? Did you mean a round is better than the 3x10?

Your duct is the smallest possible for a kitchen. In that sense it's not optimal.

6 inch round is about equal to 3 x 10 rectangular. They are both the smallest ducts allowed.

-david

exactly.

If the blower in the hood you select is designed for a larger duct, you will not get the cfm performance that the blower is capable of delivering, and you are likely to get more wind noise. Generally, larger ducts are better.

Cross-sections...

6"Ã: 3*3*3.14159 = 28.27

7"Ã: 3.5*3.5 = 38.48

3.25" x 10" = 32.50

(I use 3.25 because that's a standard size and I assume what you really have.)

So if you find something that requires 6"Ã you've got more than enough.

My guess is it wouldn't be the end of the world to use it with a hood that asks for 7". Roughly 15% smaller. Not ideal, but I doubt you'd notice the difference on anything but the highest setting. Is it a nice straight path? That could offset some of the negative. Again, this is just my "guess", and I'd definitely switch if required, unless it was a major ordeal to do so.

positano, I got this from a reputable company about ducting and connections
 The ducting should be as short and straight as possible, and the number of sharp bends should be minimized.
 For most efficient air extraction, the diameter of the ductwork should not be less than 6". Use of flat ducts also reduces the air extraction efficiency.
 Noise levels of the hood will increase if flat ducts or round ducts of less than 6" in diameter are used.

The subject of grease collection in ventilation hoods is a complex one and subject to significant research and measurement. My generalization of some reports I've found is that neither screens or baffles collect more than about 30% of the effluent, and that which is collected comprises the larger droplet sizes. The hope is that the smaller sizes stay in the air stream until exhausted.

There are hoods that use baffles backed by other media that collect more of the the total particle distribution. There are ventilation systems that just suck all the stuff into the ceiling and use strong UV to inert it before exhausting it. So baffles are not the only game in town, but are considered adequate for many applications so long as the duct velocity is kept in the 1000 - 2000 feet per minute range.

kas

Hi y'all,
Well it's time to consider the hood again...
Just wondering if anyone has ever heard of or had any experience of a hood that doesn't seem to have a brand name, but is sold on this site: http://tomorrowskitchen.com/range_hood_FAT2W36.html
It may be this stores own manufacture? In fact, the name of the hood looks like FAT2W36. They seem awfully confident of it (3 year warranty) & the noise level appears to rival Kobe.

Never mind about that last question; I just spoke to their rep & the warranty is such that labor is not covered. One would have to send them proof of the issue by either image or damaged part, itself & they send out a new part. Owner is responsible for install and/or repair fees to third party. And there is no brand (as I thought might be the case) they have it made in China by manufacturer (who they say produces many brands like Cavalier, etc.) But it looks good and the noise level is quite low, according to their claim.
Kobe's warranty is 2 years and they send out the repair dude. For that alone, I do believe I may be heading more in Kobe's direction.

When we chose our hood I was convinced by the distributor that the optional restaurant style baffles would be a bad choice for the home. The argument is that those baffles work because turbulent flow causes grease to drop out of the air stream. On low speeds you don't get enough turbulence for the baffles to work well. I'm not a fluid-flow guy, but this rings true to me. We chose a Broan hood with the standard metal mesh filters and we run it at low speed except when frying with high heat.

Can anyone out there with fluid dynamics know-how comment on the baffle issue?

Yes, this is what I was told and sold too. It was worded a bit differently but it amounts to the same thing. Basically, baffles are not good at the lower end of the air flow speeds that we see in this site. Note also that people who post here are strongly in favor of "big" so many of them have big blowers and high air speeds.

HTH
-david

Thanks to all of you for the great info. I did get the Kobe with oil filters a couple of months ago. It is very easy to clean and works great. I'm not happy with the lights on the Kobe, but that's a different story.

Thanks again!

Glad to hear you like your hood, Positano.

But about the baffles; when one says they don't function well at low speeds, what does that mean?