Once you have picked a hood that will overlap the cooking area by enough for capture of a high percentage of the effluent per hvtech42's comments above, you should strive for enough air flow to achieve good containment. In my view, this requires (at full blower power) a specific flow rate of approximately 90 CFM per square foot of actual hood aperture (not the outer bounds of the hood size) which is equivalent to 90 ft/min average air velocity. Further, because there are pressure losses in the baffles, hood transitions, ducting, and make-up air supply, the rated performance of the blower must be higher to meet this value. A decent margin would lead to selecting a blower that, at zero static pressure where such blowers are specified, had a factor of 1.5X the value obtained above from multiplying 90 by the square footage of the hood aperture area.

Room size is irrelevant, but some adjustment to size and flow can be argued based on whether all four sides of the hood are open to the room, or the stove is against a wall that helps direct some of the expanding and rising cooking plume into the hood. The velocity required is proportional to cooking temperature (and with gas, the influence of flame temperature on the temperature of the entirety of the rising plume). The aperture area needed may have to grow if cross drafts are expected to be routinely influential.

One might visualize that if the plume is rising at 3 ft/s and a cross draft is flowing past the cooktop at 1 ft/s, the rising plume will be significantly bent away from vertical, increasing the amount of effluent that misses the hood aperture.

kas

I think I can grasp some of what's being said there. Assuming a hood has say 4sqft of capture area, then I'd need aprox. 4*90*1.5 cf. (540). Here's the hood I'm looking at: http://www.kitchenhoods.ca/shop/victory-twister-42-professional-wall-hood-with-rotary-switches.html

Also, I'm assuming I was correct when I ignored the salesperson's suggestions that 36" width is plenty.

I like the baffle filters, but my issue with that hood is the depth. Only 22". If you're going to go the extra mile might as well go all the way.

I guess the issue I'm running into is finding a reasonably priced large hood. Even when you bump to 42" width there are significantly less options. As you mentioned, one can end up spending way more for ventilation than the cooktop itself (and being as the cooktop is ~$1200 CAD, that likely isn't difficult to achieve). I realize I may not achieve the "ideal" setup, but am at least to understand where the sacrifices are being made.

Here's a 24" depth model by the same company: http://www.kitchenhoods.ca/shop/victory-twister-max-42-high-cfm-wall-hood-42.html which isn't too badly priced...the issue I have with this one though is it jumps to 1000 CFM and twice the noise level which is certainly un-ideal.

If you had the choice *only* between 42x22 and 36x24, I would go with the narrower and deeper one. The 18kBTU bad boy on your cooktop is in the middle and the 2" extra depth would matter much more than the sides overlap.

Having said that, the 24" hood you listed above is very nice and I'm not sure that it's noisier than the 22". On its lowest setting it has 0.4 sones (as opposed to the 0.7 of the 22") while the maximum noise is given for 1000cfm (as opposed to the 750cfm of the 22"). At the same airflow, I think that the 24" is less noisy. Go for it!

"Also, I'm assuming I was correct when I ignored the salesperson's suggestions that 36" width is plenty."

Well....., plenty for some is scarcity for others. :)

Rarely is there so much space, funding, and time to be able to avoid trading among affordability, performance, and aesthetics. Most will try to find a sweet spot among these where "good enough" applies. Even given a full understanding of all the performance capabilities and issues, in most households there will be a limit to what can be spent and what can be visually tolerated. Otherwise, a giant commercial hood would be best for collecting every grease and odor molecule, with attendant high CFM exhaust and MUA systems.

kas

gigelus2k13: where did you see the 0.4 sone spec? If I go to specs on that one it shows the min as 1.5

I was looking at the 36x24, which claims 0.4 to 7.1 sones.

I'm beginning to suspect that the noise specs they're listing are a little bogus. As the 36x24 and 42x24 are probably using the same motor and fan (same airflow, same rpm) and the same material (19 gauge SS), they should make about the same noise. The difference between the 0.4 to 1.5 sones on the lowest speed is too large to have any explanation except a different way of measuring the noise or simply pulling the numbers out of their favorite place...

Which hood did you pick feens81?

feisty68 we ended up going with the Zephyr Venezia ZVE-E42CS. Probably our biggest splurge in terms of spending more than planned on an appliance. However is one of the few hoods that hit all of my desired specs: 42"x24", ~600-700cfm (715), quiet (0.8 sones on lowest speed).

The problem I found is that with the footprint that big, most hoods were 1200cfm and started at double the noise rating. We got to listen to a similar hood (same noise specs) and it's barely audible on the first two speeds.

Thank you feens81. Sounds like you are not using it regularly yet. I hope it meets your needs :)

I actually don't even have it yet. Our appliances arrive this Thursday.

Thanks for replying feens81! Fingers crossed that this hood ends up working for you :)

@feens81 - do you still like the Zephyr Venezia? I am looking at the same exact range hood (in 42") to match a Fisher Paykel cooktop (80,000 btu if all used).

Many thanks!

D B that hood was a superb choice. Most of the time we run it on the first two speeds and it's quite quiet. Plus it still has 4 more speeds if I need to clear the air more aggressively. Having the baffles is also great. So easy to just toss them in the dishwasher when needed.