If it was a choice between having a recirculating system or venting through the garage, the latter would definitely be my choice. You shouldn't vent into the garage itself. Vent to an outside wall of your garage or perhaps you could go out the garage roof. Can you return your purchased hood vent in favor of something that would work with your existing ductwork? Possibly using an external or in-line blower if that would work? In my situation, my ductwork runs from an interior wall up two flights, attic to an external blower on the roof. It has 3 elbows as well but works well. A better option than reusing my old downdraft or a recirculation system IMO.

>>> would a recirculating hood such as a Broan cbd330 make much of a difference in grease and odors vs no hood at all?<<< >>>I also know what CO is and why I should care about it.<<< >>>Our house is old and far from airtight.Is my hunch that this recirculating hood won't do much good right? Would it mitigate eau de cabbage stew any better than cracking a few windows?<<< My initial reactions to using that Broan without venting to the outside are these: that your Broan may help a bit with some aerosolized cooking grease (although the hood design means that a lot will not be captured); that the Broan may serve as a surface for condensing vapor but will be otherwise ineffective in dealing with vaporous combustion byproducts and steam, much less the odor/stench of boiled cabbage; and that it will do nothing about CO which you should not need to worry about, anyway. For removing odors when boiling cabbage etc., you might have better luck with the windows, particularly if you can toss-in a box fan or window fan for those occasions. CO emissions from modern gas ranges should be barely detectable with sophisticated equipment -- far below hazard levels --- unless somebody has really screwed with your burner adjustments The combustion byproducts from the burners are rather more smoglike with the principal components being CO2 and NO2. The Dept. of Energy in conjunction with the EPA published a study on air quality in kitchens with "unvented" gas ranges and the effectiveness of realtively affordable venting a couple of years ago. The result was some overblown media attention. It also got some interesting commentary here which you can find at this link if you are interested: http://ths.gardenweb.com/discussions/2304651/ny-times-the-kitchen-as-a-pollution-hazard The idea of getting a convertible hood and later installing outside venting is not a bad one. I'm guessing that you are not currently venting because your stove currently sits on an interior wall and you all have been stumped on how to get outside venting without a full kitchen remodel to relocate the stove. Is that correct? That's a problem I had with my old-house kitchen and I discovered numbers of relatively easy ways to go up from a vent and run ducting over to the nearest exterior wall through a cabinet. This was easy for me because the interior wall behind my stove butted into an exterior wall and because I didn't mind the somewhat industrial look of the ducting. Might or might not be that easy for your old house-kitchen and the look might or might not work for you. Having said that, the 30" Broan cbd330 may not be the best choice. It seems to be a low-rise hood which does not project very far out from the wall, and it has a flat base rather than a canopy. As kas has often pointed out, an actual canopy gives better coverage and capture and can be a significant part of the effectiveness of a range hood. Even better when the hood extends a bit wider than the stove. (Better still when the hood also has enough depth to extend as far out as the front of the stove, too.) Basically, the flat base on the Broan means that the unit depends entirely on fan-power to collect vapors, grease, and etc., The Broan has relatively low fan capacity. (250 CFM?) You might want to consider taking that unit back and swapping it for something with a canopy and, if it will fit, something 36" wide. Again, that may or may not work in your kitchen. My old-house kitchen was such that I also had to resort to a low-rise hood with a flat bottom rather than a canopy. We work with the kitchens we have.

Your design is very much driven by wishful thinking. I understand. I've been there before. You'd really want it to work this way, and it's frustrating that nobody makes the appliances you want. A downdraft hood is close to useless, with one noteworthy exception, all recirculating hoods are no more than expensive white-noise machines, and even if you could fit in that place, a wall oven really doesn't work well under a countertop let alone under a cooktop. Pretty much the only thing you have going for you is the induction cooktop. That's a solid choice. I suggest you go back to the drawing board and pick a more conventional set up. A induction cooktop, a vent-a-hood recirculating island hood, and a wall oven at countertop level should result in a much more functional kitchen.

I haven't searched for one, but it is possible that Broan/Best has a recirculating system with both grease filtering and charcoal-based odor filtering. To the question: Generally baffle filters are superior in grease extraction efficiency. This is why commercial hoods use baffles. Specifically, the baffles remove the larger end of the particle size spectrum while retaining their performance no matter how much grease is collected. The smaller end of the spectrum is expected to (hoped to) exit the system on the roof. The pressure loss of the baffles remains the same, greasy or not, and this allows the overall air flow to remain constant. However, baffles work by centrifugal extraction due to the air making two reversal in the baffle space. This requires some minimal velocity that likely depends on the details of the baffle design. For modest cooking where low blower speeds are adequate, there is a point where mesh filters -- if kept clean -- may become superior grease collectors. Mesh filters work by impingement. A hybrid baffle system seems to be intended to filter by mesh while providing the appearance of a baffle system. In some commercial applications, the stringent filtering requirements lead to stacked filters, the first usually being baffles, followed by mesh, ball bearing, and other schemes that address different parts of the particle spectrum. UV disassociation of grease and odor molecules is also popular.