Good enough is in the nose of the beholder.

The actual flow rate will depend on the pressure losses from the hood transition, hood filters/baffles, internal transitions, ducting, and whatever negative house pressure results from insufficient make-up air replacement. Without knowing all of those parameters, it might be useful to just assume that you will get about 2/3 of a fan's zero static pressure rated cfm when actually operating the system. If that value for the 8-inch option corresponds to whatever rule-of-thumb you are using to define good enough, then it is good enough to meet the rule. Other rules should be considered to ensure that you haven't been using the most optimistic rule.

kas

I would be happy with the 8XL.

High end European manufacturers sell hoods with maximum CFM's far lower than that, and this little fact tells me that any number of CFM greater than that will be fine. You must plan for new air to replace the out-blown air.

i looked on the web to see the shape of the Prestige 36" low profile. I am impressed. It has a capture volume. Its filters are placed to allow steam and smoke to rise into a catchment basin. Plus, it's low profile. Congratulations gravitypulls! I wonder if they can cut a window in the front panel. Put a panel of polycarbonate or tempered glass. I would install the hood as low as possible. I would not mind having to step back a bit to see the stuff on the back burners at an oblique angle, or to pull it forward is bit when I wanted to look straight down into the pot.

House is about 50 years old, so not so air tight. Duct run is straight up from the hood through the attic/roof with no bends (maybe 10ft).
The drawbacks to the 10xl are
1. more duct space in cabinet
2. would probably require make up air on high even in an old house
3. louder than 8XL ~82db vs ~79db

If I thought the 10xl would make all the difference in the world then I wouldn't hesitate to get it.

It looks like today Prestige has the best and maybe only off the shelf seamless, 304 stainless, infinite speed fan control, low profile, baffle filtered hood out there. Hope they make a good one.

We have the Fantech 10XL in our system. We also opted to install the LD10 (basically a big muffler) in the system as well. Obviously, the fan motor is mounted up in the attic about 7' away from the hood itself. We are using the Fantech 48" hood liner. In retrospect I wish I had a 54" hood liner but I was in a rush and this is what we wound up with. I find that the 1266 CFM from the 10XL is not excessive. Also the noise of the system with the LD10 in place is not bad at all. Based on the numbers (82 db vs 79 db) I doubt you'd be able to notice a difference.

Go with the 10XL and run it at a lower speed. That way if you need more oomph it'll be there for you.

I went with the 10XL because we had an existing 10" roof penetration and I was lazy. I kinda wish I had the 12...

~82db vs ~79db
This is the same amount of noise to human ears.
It's 8 Bels, or 80 deci-Bels.
Instruments can measure the slight difference but it's not audible.
BTW this noise measurement is a relative intensity when measured in comparison to another noise that is deemed the starting point, and that starting point noise is not a "standard" it is their choice how to manufacture the reference noise. In other words, do not look at dB specs except when looking at one manufacturer's various products, and then only as as a rough guide. Some people look at clouds to predict the day's weather.

Thanks all,
laranbrian, If we use the 10XL I think it will be running at a lower speed most of the time. If you noticed, does the motor itself get much quieter/louder when you turn it down/up? I know the whoosh is going to come down a notch when it's running on low, but not sure about the motor. Definitely getting the silencer regardless of which fan.

There is a significant decrease in the noise as one throttles back on the motor. At a given amount of CFM of movement, the 10" will generate less noise than the 8" (less rotor tip speed to move the same amount of air = less noise). 1266 CFM (or realistically 1000 CFM) is *not* a huge amount of air. There won't be gale force winds sweeping through your kitchen and out the vent... Although I did manage to suck a paper towel from my hand and through the ventilation system once.... =\ Oops.

A 3 dB increase, if identical in frequency distribution, should be just discernible as louder.

Zero dB is a standard for acoustic noise (20 uPa, rms), but there are different filter shapes used for different purposes, and these will lead to different readings.

In any case, the fan is separated from the hood by a duct, so the sound level at the cook's ears will be different from that from measuring the fan alone. If the character of the noise is different for each fan, and the duct is frequency selective, as it may be, then the louder fan in situ may not be the louder fan under test.

kas

Yes, in situ you will see and hear. I waited before buying the silencer (for an inline fantech blower). I installed the blower and observed in situ. We decided not to get the silencer. Our noise is the whoosh of air that is inevitable, not frequencies that a silencer would annul.