More about kitchen venting hoods

Anticipating a new roof in the near future, we've been looking into also adding a venting hood over the range oven combo. The range is on an inside wall and has a basic residential grease trap "hood". We like high-temperature stir frys, deep frys, and (ultra messy) fried onion and chili pastes.
In another thread someone mentioned a downdraft venting range. Do they really work? That might be a good solution, venting down and under the kitchen floor (in a crawlspace ... except there is some ductwork there already)) and out the wall near ground level. The other option is a standard vent, up through a cabinet, crawlspace, and roof.
Someone here mentioned venting a hood down under the floor; how is that done? Where would the vent pipe go?
Is it necessary to have the fan at the intake point, or can it be installed somewhere inline or at the exit to the outside?
Thanks,
    Una
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Does such a thing exist, in the usual format of oven under cooktop?
    Una
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Have you ever noticed the grease on the huge fan covers outside of restaurant kitchens, especially where stir frying is done?
Companion question:
Can you imagine lying on your back in your crawlspace, trying to disassemble and clean filthy, greasy ducts?
I think this explains why you would not want ducts going down, in your situation. Actually, any sort of ductwork for kitchen venting is a horrible idea, and this is why a range should never EVER be on an inside wall.
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High temperature stir frying and deep frying is minimally greasy, if you use a good high temperature oil. However, when you add the food ingredients to a stir fry there will be some rapid boiling in oil and that causes steam with some oil carried along with it. At least it is not burned oil.
Maximum grease load results from grilling (we do that outdoors) and the European technique of searing a hunk of meat before pot roasting. Oh, and any paste fried in oil; that generates a lot of oily steam and it is a key technique in some Indian and Mexican dishes.

Yes. And I would much rather do it under the house than under the roof!
I used to live in a house with a downdraft cooktop (oven was on a wall) and it was only fairly effective. Certainly better than an underpowered recirculating hood. But we have a standard range: cooktop over oven. Short of a total remodel of the kitchen, the range will have to stay where it is, on an inside wall. On the whole, I am favoring a straight vertical vent through the roof, with a high-power "Chinese" style fan. Can I get a closing cap? Or would the fan be strong enough to lift a hinged cap without too much compromise of the exhaust? How drafty are these through-the-roof vents?
To vent a hood down, I would have to open the wall cavity, and maybe also build a box out from the wall, so the range would protrude out of the counter by a few inches. And the outlet would be at knee height right beside our entrance.
Good brainstorming here!
    Una
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Una wrote:

We have both kinds of vents, as the cooktop is an old JennAire electric with interchangeable grill/burner set. Our downdraft is very powerful and probably would not work with gas. The fan is centered, between burners, and there is a "well" that is lower than the fan and collects a lot of grease. There is also a steel mesh filter before the fan. We are on first floor, slab, so duct goes along inside of cabinet, through my broom closet, and then out. I hate the whole contraption, because it is a glob of grease. I like to grill outdoors. The ductwork for the downdraft vents right next to our front door. Odd arrangement, but it is a condo. No sign of grease on the outside, and we use it a lot. I do stir-frying, but the whole point of that is to use minimal grease. Chinese stir-fry was invented to conserve scarce fuel - the cooker has a small bottom to concentrate heat and uses liquid in the food to cook by steam.

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My in-laws have a gas JennAire with the center vent and it works fine.

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The success of such a system depends to some extent on what kind of cooking is being done. The OP said "We like high-temperature stir frys, deep frys, and (ultra messy) fried onion and chili pastes." At some point which is tough to determine in a discussion like this, any system will be unable to handle the mess. And/or, the ductwork will get atrociously filthy and begin to stink.
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The "Chinese hood" that I referred to in my other post had some sort of unique filtration on it which made it compatible with that type of cooking.
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I had customers a while back who had a cooking style similar to yours. They had just remodeled their entire kitchen and the type of hood exhaust fan that they got was for "Chinese kitchens" I don't remember the brand, but they told me it worked very well for their lifestyle.
Commercial kitchens usually have the exhaust fan outside or on the roof, but the type of fan that they use may be too powerful and unattractive for residential use.
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NuTone/Broan make exhaust fan and motor that fit on the roof to allow a larger power unit and quieter operation, I have had one for many years and they work great for our type of cooking.

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EXT wrote:

Hi, If you do that kind of cooking, then go to a restaurant supply outfit. They have stainless hood and fan for commercial use at various size. Pick one and do it right first time and forget. Most Chinese folks have this kinda set up in their kitchen.
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Yeah, and be prepared to shell out $1000 for a used one.
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The one I have cost me $220 including shipping from Ebay. It was a brand new unit, made in Canada. Both motors were made in Japan with lifetime warranty - I don't know how to apply though as it does not come with a phone number or address. Rated 680 ft^3/m. Good workmanship. It has been worked great so far. Except it is noisy, particularly when both fans are on high.
Oh, yes, I am a Chinese. We do lots of cooking.
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The NuTone website recommends min 1 CFM per 100 BTU; is that BTU of the highest BTU element, the total BTU of all elements, or the total BTU you are likely to use at one time?
Can the "out the back" rectangular duct be run inside a wall? 3.25x10in should fit in most walls, if framing is at least 2x4 and 12in or greater on center. That would involve a turn, from horizontal to vertical, but would save the cabinet over the range.     Una
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Typically, the most efficient and quietest systems are ducted to a roof fan where the motor is in the roof mount. We just did our kitchen over and used a 10" OD round duct fitted to a Wolf commercial-style (but residential design) hood and roof duct. The setup is 900CFM and we have a five-burner gas rangetop. I honestly forget what the BTUs are, but another concern is having the hood not too far from the source of the heat/steam/grease/etc. and of course not too close either. I don't think you can build a very efficient system within the confines of a 2X4 wall. If you had 2X6 that might help. BTW, the hood we have is Wolf Pro Hood 36":
http://www.wolfappliance.com/Ventilation/ProWallHood
The Range is the following:
http://www.wolfappliance.com/GasCooktops/CT36GGasCooktop
I have to also note that my wife absolutely loves this setup. Cleaning the solid stainless steel hood louver modules is easy... lift the module and pull it out of the frame, pop in dishwasher and the reinstall. Same as in my son's restaurant.
On Wed, 06 Feb 2008 22:23:04 GMT, snipped-for-privacy@att.net (Una) wrote:

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