At least 42'' width.

27'' depth is nice if you don't hit your head on it. It's obvious, but more capture area is better.

Height above range: 30'' optimal but many will bump heads at this height. As you raise higher, your capture area must expand to account for increased lateral spread of the effluent.

Cfm? Again, with some exceptions, more is again better. There are few reasons IMHO to undersize a blower. The difference in cost is modest, and the ability to really cook hard with no smoke etc escaping is wonderful. Higher cfm do create some issues:
1) makeup air: this is a constant source of argument here. I know weissman for example feels it's necessary for 600 cfm. I vigorously disagree: as long as your code does not demand it. Most houses, other than ultra-tightly sealed houses, have plenty of air infiltration. And, again, worst case scenario you crack a window. Admittedly that's less optimal in Minnesota in winter, but remember that makeup air is also introducing frigid air into your house, unless you're using a fancy heat exchanger, which about doubles the cost of the installation.
2) noise: more cfm are louder. This can be elegantly eliminated in many cases by using a remote blower. However, if you're going straight out through the wall, that is not really an option. Even an external wall mounted remote blower will be so close to the hood that it will not really help the noise much. So, while a supershort duct run does help from a ventilation performance standpoint, it is actually a disadvantage from a noise standpoint.

There have also been a few posts in the past here suggesting that at least some hoods require a minimum length of duct run to work well. I'd check with your hood manufacturer first to be sure. I am also not sure how you mount a backdraft damper on such a short run--on the outside I guess? Without it, of course, every time the wind kicks up it will blow in through your hood. Another potential disadvantage of the through-the-wall ducting is that your backdraft damper, or at least the external exhaust outlet, will be highly visible on the side of your house, an issue depending on how exposed that side of the house is.

Remember too that if you install a hood with an infinitely variable fan speed control (MUCH superior to the typical Low-Medium-High switch on many hoods) you can always dial your ventilation down. To restate the cliche, you can always run a high cfm blower at lower speed, but you can never get a low cfm blower to crank up beyond its rating.

How many cfm? I think 750 may be inadequate for a 6 burner BS. Using one quick rule of thumb promulgated by Wolf, it's 1 cfm for every 100 BTU, and that's the SUM of all the burners you have. I don't offhand know the burner config of the BS, but if you have three 22K and three 15K burners as an example, you have 111K BTU, which argues for a 1000-1200 cfm blower. You can do the correct calculation for your exact burner configuration.

Finally, I will put my annoyingly repetitive plea to consider multiple brands of hoods. I have yet to hear of an appliance store selling more than one or two brands of hoods. Thus the "VAH is the best hood out there..." line you always here from dealers who (surprise) only carry VAH. You have recommendations above for several good sources. I'd add Independent, and of course my favorite, Modern Aire. The latter built our custom 64'' hood liner. It's gorgeous, works fantastically well, was quite cost competitive, and was totally custom. I specified the exact width, depth, and height of the hood, as well as the location of the duct collar, and had the light and variable speed fan control mounted on the wall beside our range, rather than underneath the hood, about as inconvenient a location as I can imagine. Plus, I worked on a daily basis with Jeff Herman there, who helped me decide on size, configuration, choice of blower, etc every step of the way. I still correspond with him now just for fun.

HTH.

I have a BS 36'' RNB with grill and a Prestige 42x27 hood with 1200 CFM blower venting directly through the wall. The hood is mounted 35'' above the cooking surface. Works great, even with heavy-duty wokking. We've used the grill only sparingly so far, but no problems with that either. Clinresga is right about straight throught the wall not being the best from a noise standpoint. We were told it would make no difference if we used an external blower and to save the $ and just get the internal. I wouldn't call our configuration whisper quiet, but on the lower end of the variable speed range, where we set the fan for everything except wok or grill cooking, it is no problem carrying on normal conversations or watching TV. Our house was built in 1917, so make up air is not an issue, even though we've replaced almost all the windows and most of the kitchen is in a new addition. Good luck with your decision.

clinresga, What do you think of the range hoods by Metallo Arts? you seem to know alot so i figure i should ask. thanks

Reposado...

You have the almost the exact configuration that I am considering purchasing, only I am looking at the 42x24 hood from Prestige. From what I can tell, the 27" models have the Solarod warmer, which I have never seen in pictures or in person. Does this decrease the capture area significantly? I have no need for any type of warming lamp, but I would like the increased depth of the 27" if it did offer more capture area. But, if it is taken up by the lamp, I wouldn't bother.

Sorry to the OP for getting a bit off topic, but hey, we're still talking hoods.

First I would like say Clinresga hit the nail on the head, at last somebody who knows what they are talking about. Second where did you get this education?

victorianjane: nothing from personal experience. But there is at least one big Metallo fan somewhere on this forum, and just based on their website, they look like a company I'd like--small, dedicated to hoods, ultra high quality stuff. I'd do that in a minute versus the mass market VAH--if it fits the budget.

reposado's setup sounds sweet. 1200 cfm through an ultra short duct run should really kick butt. His comments re noise are what I'd have expected, but as he (she?) points out, particularly with a variable speed control, you'll run this hood at way less than 1200 cfm most of the time. I would tend to agree that with a duct run of a few feet, an external blower is not worth the money or effort.

So...since the OP doesn't appear to have dropped back by, I'll lurk here for a while.

dhc8, the Prestige solarod is, as the name implies, just a narrow heat lamp rod running along the back of the hood. It takes up very little of the depth of the hood and doesn't significantly diminish the capture area. I use it infrequently, but occasionally it's nice to be able to hold a dish for a dinner party (and one of my two labs has now learned how to open our bottom mount warming drawer and I haven't yet rigged anything up to stop him). The capture area extends from behind my back burners to in front of my front burners. We have not had any problem with escaping fumes (except when my daughter forgot to turn on the hood before cooking).

The primary reason some localities require make-up air (MUA) systems is safety. One should not pull a partial vacuum on a house that uses certain types of water heaters or furnaces that do not have a separate source of make-up air or run very hot exhausts. Carbon monoxide and other effluents then become problems.

There is also a fireplace or wood-burning stove issue. A negative pressure of a tenth of an inch of water may be sufficient to mess up a fireplace draft, particularly if the fire is damped down.

Independent of the local law, whether 600 cfm or 1000 cfm of exhaust is enough to cause too much negative pressure will depend on the house design and whether one tends to leave certain windows slightly open, even in winter. (1000 cfm of MUA would require a fairly large window opening.)

Because my plan is to be able to pull up to 1500 actual cfm from my kitchen at full exhaust fan power, and provide 1000 cfm of MUA, and wanting the fireplace to work correctly, and living in NH, I will have a heated make-up air system. The heat will be pulled from my hydronic heating furnace via a heat exchanger (like a car radiator). Others with sufficient need and space may find propane or electrically heated factory turn-key MUA systems suitable.

I suspect that the rare and short periods of time in which significant heat needs to be added to make up for maximum air exhaust in cold weather might justify electric MUA heating versus the somewhat more complex and perhaps harder to plumb but lower fuel cost hot water MUA heating.

kas

kas
just came across this post very belatedly. I'm interested: did you ever consider a passive heat exchanger, rather than the active hot water system you're using? They look attractive from the energy standpoint, though awfully expensive. Is it just not able to heat MUA enough in your (brutal) NH winters?