Because they work so badly to begin with that they are almost not worth bothering with. If venting is worth doing, it's worth doing right--with an overhead vent.

They probably make them the way they do because 99.9% of the people who install them have to make them fit in a 24" cabinet behind a cooktop. It wouldn't be cost effective to manufacture a unit that practically no one would buy.

Why do people build or design kitchens that aren't more adaptable to overhead ventilation?

OK, you two purists, here is the reason why I couldn't do overhead venting: there was NOWHERE to put it! Above my 8'2" ceiling, directly above it, are the 2x12's that hold up the second floor, and they run perpendicular to the direction that the ducting for an overhead vent would have to go. Cut through the 2x12's for venting, or have an ever-so-attractive soffit box running from the hood to the wall? Nah, I don't think so. There is, however, a nice crawlspace under the house.

Next, there was only one piece of exterior wall large enough to hold a range or cooktop that a vent might go through. Putting the cooktop there, however, would have cost me a roomy pantry, as well as a prep sink that I use every time I cook, and the size fridge I needed, and have made for a useless, stinking mess of a layout. I suppose I could have boarded up a view-window to add more wall space, except that my city design-review nazis would never have approved it.

Finally, I hate cooking with my back turned to my companions. The cooktop HAD to go in the island, and a downdraft was the only hood alternative. Sneer if you like, but I don't think that I'm the only person who has ever wanted both a downdraft and under-cooktop storage, and flexible design sure seems to be one of the hottest trends in home appliances these days, considering the advent of dishwasher drawers, component refrigeration and so forth.

So let me see if I have this right....

Because you decided your cooktop had to go in a particular awkward place, and because you couldn't possibly get by with a different refrigerator, or do without a prep sink in a particular spot, and because you can't can't be expected to cook with your back to your audience, etc., etc. -- the downdraft makers are at fault because they haven't created a product that conforms to your very specific and exacting needs???

Get real!

Mollyred, I can sympathize with you. We've got a 1600CFM downdraft, and while it does an okay job, it's far from perfect. An overhead vent probably could have been an option for us when we remodeled, but it would have led to a much less satisfactory arrangement of the rest of the kitchen, an arrangement which would have certainly caused me more grief than the downdraft does.

Would a remote blower work in your situation? We have one, mounted outside on the back wall of the house. This gives us lots of room in the cabinet under the cooktop. I would say that only 2-3" is taken up by the part of the downdraft which has to be in the cabinet.

I just read your original post again, Mollyred. I didn't catch that you've already got a remote blower. I guess, either I'm missing something, or your setup is totally different than mine. I still sympathize, though. Sometimes it's just not possible to get all of the pieces to fit together in an ideal way.

Mollyred, in my opinion Live Wire Oak is right in response to your question. That is, that downdrafts are for set-ups like yours where it doesn't work out to have a proper hood. And since they don't sell that many, proportionally, because the basic physics will always make over range ventilation work better than downdraft, they don't put a lot of R&D into it.

But I don't understand why people are being mean about it. Some people put their cooktops in islands just for the looks of it, and choose downdraft even though they could have hoods, just for the looks of it. And they could want a set-up like yours if someone would design it right.

I get it about the fridge and the pantry. They're part of the utility of the kitchen, after all, not luxuries, and it's not like you can put them in the island!

Mollyred,
Gaggenau makes a nice downdraft called the VL051. It is expensive but would fit 95% of your requirements. It is probably the only downdraft I would ever purchase as a purist. For a four burner cooktop, you will need two, one on either side of the cooktop. They allow you to use the drawers under the cooktop.

Good luck!

Jamesk - I don't understand your hostility. It's as though you're saying that I'm stupid or foolish for not being able to make an overhead hood work in my kitchen. That's not really in keeping with the tone of this forum, which is generally empathetic and supportive. We may challenge one another intellectually, but not personally.

Do you find something wrong with not wanting to have my back to my guests as I cook? Or with wanting to have a design that is ergonomically efficient and comfortable for me? And since the engineering modifications that would go into a reversible downdraft are trivial (i.e. making a faceplate and attachment to the activator that can be flipped) is there some reason why my making the suggestion disturbs you?

Your second post also suggests that you didn't understand my previous descriptions, To make it as clear as possible for you, I only had one piece of wall, 8.5 feet long, onto which an overhead hood could have been vented. Had I done so and put a cooking surface under it, I don't think that I could have squeezed any sized fridge in there too, because there are windows on either side of that space, and our city requires a distance from a cooking surface to a window, even if there is a hood over the cooking surface. That means that the fridge would have either had to go less than a foot from the main sink, with no other landing space around it, or into the area where the pantry is now, cutting out 2/3 of the storage space there, again with no landing zone unless I cut into the pantry space further for a counter.

Putting a cooktop in that location would have also made the distance from sink to cooktop around 9 feet, and from sink to fridge more like 18 feet unless the fridge were jammed directly next to the main sink. That's way too long for an efficient work triangle, and would have made it very difficult for 2 of us to share the space. Had I tried to put a prep sink in to the left of the cooktop, I'd have had to plumb an additional 20 feet of water lines and sewer spur, to gain a prep sink and about 18" of prepping space. Putting a prep sink in to the right would have pointless, and into the island would have been another 17 feet of plumbing, plus the opportunity to drip on the floor as I moved things from the prep sink to the cooktop. Those are the layout problems that I abbreviated as a "useless mess."

Instead, I have a comfortable, roomy, elegant design that works beautifully for 2 cooks and gives me everything that I wanted other than that damn downdraft hood.

If you are so attached to an overhead vent hood that you would give up all the rest of those advantages in order to have it, then by all means you should have it. I might not understand your decision, but I wouldn't fire sarcastic criticism at you for having made it.

Mollyred - You're missing my point. I'm not pushing overhead ventilation at all. Your original premise was that the downdraft ventilation manufacturers were "user-unfriendly" because they wouldn't accommodate your unusual and specific needs.

Following the same line of reasoning, you could just as easily blame some other culprit. In fact, the root of the problem seems to be your inflexibility on the kitchen layout or your unwillingness to compromise on the under-cooktop storage. Everyone planning a kitchen has to work within the constraints of structural limitations and equipment specifications. Why would you expect your design to be so special that you can label manufacturers as "user unfriendly" because they don't offer a product that matches your very specific and unusual situation?

You could just as easily complain about those bullies at the overhead vent manufacturers. If they weren't so "user-unfriendly" they'd have figured out a way to vent an overhead hood around something as common as a beam -- right where someone might insist their cooktop needs to be located. Surely if the manufacturers put their best designers and enough manpower into solving that dilemma, they could maybe sell dozens of them! Of course, they'd probably lose money on every single one sold, but how user-friendly!

As I said earlier, I'm not advocating overhead ventilation, you're more than welcome to use whatever system you prefer and to arrange your kitchen however you wish. Just don't complain that you were forced to install your ventilation system in some unorthodox fashion, and now it doesn't perform to your expectations -- all because those downdraft manufacturers are so "user-unfriendly". The decision to deviate from the manufacturer's specification was yours -- not the manufacturer's.

The fact is, manufacturers are NOT user-unfriendly. They'd be happy to build and sell anything with enough demand that it becomes profitable. For the most part they do a good job of providing what consumers want. Can they match a product to every single consumer's special circumstances? No. It's up to the consumer to design and build within the parameters defined by structural limitations and with the products available in the marketplace.

Jamesk - I disagree with your assumption that my desire for storage under the cooktop is unique, but welcome the relaxation of tensions in the discourse.

I'll bet most people who have downdraft hoods would reply with a resounding "YES" if they were asked if they would like to have storage for their pots and pans and utensils directly below their cooktops. Isn't storage at point of use a fundamental principal of ergonomic design, and wouldn't the importance of this grow in reverse proportion to the size of the kitchen? I just think that the downdraft producers are missing an opportunity to make their products more popular. But then again, you may be right. I might be the only person in the entire North American market who actually wants more storage right where it is most helpful.

BTW, I admire your kitchen a great deal. The layout is nothing like mine - but I think it's very handsome.

I have the Thermador 15" downdraft with an internal blower. While I may not have drawers underneath, I have 3/4 of the cabinet available for storage below it via a false back and a door/short shelf combination. I just don't feel like it's that intrusive. Maybe that would be a good compromise for you.

Also, to offer a contrarian view on the efficacy of downdrafting (since that seems to be a perennial target in here). While you won't hear me say that it's 100% as effective as a hood, it really does a fantastic venting job for my cooking style. After almost two years, I have no grease spots or splatter. The extra height reaches above all my pots. As long as you use the back burners, you can see it pulling virtually all the steam/smoke. And anyone walking outside can usually identify by smell what I'm cooking. Someone on this board once posted a close up picture that showed the vapors pulled into the system, and it spoke 1000 words. Just in case anyone needs a downdraft for their layout, don't think that there aren't any completely satisfied users out there.

Why don't you use a recirculating island hood?!

Downdraft systems just don't work work well due to the physics involved--with a reasonable fan (even 1500 cfm), one cannot pull enough air across ther range to extract all the updraft from the cook surface.

The Thermador downdreaft is only 10" high, thus it will not work with 10" + tall stock pots. Additionally, as CallieandKarin stated, it only works somewhat well just on the back burners. I for one, hate frying on the back burners as it's hard to reach and control what you're frying, especially if you want other large pots going while you're frying. Additionally, I haven't experienced a downdraft system that doesn't influence the flames on a range top.

I have a 1200 CFM, externally vented, overhead, 40" Thermador Island vent at 32" off a 36" Wolf range, and it is still not totally efficient in removing all grease kicked up when I'm doing high heat frying--over time I get some grease vapor condensing on the external top of the hood which is hard to clean.

I'd suggest you go to an internally vented (ductless, recirculating) island hood with low profile. While recently helping a friend design his kitchen, I came across the manufacturer Zephyr which makes some nice recirculating hoods. The Atlantis model is a nice one with low profile: http://www.zephyronline.com/v2/products.php?col=elica&prod=30 , and a couple of other models if you don't like this style. If you are running standard height cabinets, it will let you have 30" of clearance given your 8'2" ceiling. And go with the 1000 CFM option.

There are other recirculating island hood options if you do a web search.

Good luck.

Here is a link that might be useful: Zephyr Atlantis hood

Thanks for all the comments, folks. The kitchen is pretty much done now so I'm not going to pull out what I have, but perhaps others wrestling with the downdraft dilemma will find their solutions in your suggestions.

The last bits left for completion are all things that DH and I are DIYing, and we've been dragging our feet on getting them done. And I've been a chicken about posting pix until it's all fixed up. Oh well. Subject for another post.