annettesdh makes some interesting points if I'm reading him correctly. First point is certainly on target: inadequate capture area means a significant proportion of cooking vapors will not be captured, and then they travel merrily around your house. I don't believe however that no matter how large the blower is sized, that it will ultimately do any significant "recapture" of fumes that have escaped the hood. It's true that if you look at it the way we look at bathroom vent fans, which are typically rated by how many times per hour the fan will exchange the entire volume of air in the bath, that you could argue that high flow ventilation will eventually exchange all the air in the kitchen, removing those fumes. I think there are flaws in this reasoning. First, kitchens are rarely small, closed off spaces the way bathrooms are. The likelihood is that escaped fumes will travel far outside the kitchen well before they are vented out the hood (annettesdh actually makes that point by referring to odors in bedrooms, living rooms etc). There's no way that any kitchen blower of any size will pull all the air back out of the bedroom and living room once they've escaped. Cooking also tends to continuously produce more effluent, whereas bathroom ventilation is generally for steam and odor produced over short periods of time, allowing for better capture. I didn't follow the point about 72 degree air outside. I'm unaware of any reference source that supports the arbitrary notion that doubling the blower capacity makes up for an undersized hood. Way too many variables there to make any generalization I believe. Weissman and I have debated make up air many times. I'm still not convinced that, outside of code and very cold climates, it's really needed unless you have an extremely tight house. But, agree with overall conclusion that bigger capture area and lower blower rating are better than the opposite (though I still favor our approach, bigger capture area AND bigger blower rating!).

Thanks everyone for all the helpful information - questions and answers - on these forums. As someone pointed out, it is hard to know exactly what to do in each case, even after extensive reading on GW. If anyone has the patience, maybe they could help me. I am about to order a Blue Star 48", 4 burner/grill and griddle range. The plan for our new kitchen in our renovated house shows 48" for a hood. Would I be ok with a 48" hood with a 900cfm blower? We don't want an external blower and we don't want to use up cabinet space for a 54" hood unless we have to. Our most smoke-producing activity would be grilling meat. Thanks for any advice.

Will 400 cfm be sufficient? Yes. The difference between the RCS cooktop and RNB cooktop is 15 btu. That is the will all burners on full blast. That is the same as one RCS burner. Like you said having on all burners on at the same time is rare. Having them all on at full blast is rarer still. Even at 400cfm I would still consider the RNB. Should we go for 600 cfm? You should definitely get the RNB if going to 600cfm. Any brand recommendations? Zephyr is good but I prefer Kobe. Besty by Broan, Imperial, Cavaliere is also good. Care to share your experience? My setup does not apply to you but... Ideally you want venting setup for worst case scenario. Getting way too much cfm allows hood to be quiet during normal operation. But if getting way too much venting power is not in the budget then venting for 95%-99% of the time is fine. I could live with a smoke filled kitchen once a year if I can get a great Kung Pao chicken or restaurant quality steak on a weekly basis.

You could probably get a sheet metal shop to make you something that would work for a reasonable price.