ventilation experts - please comment on this idea

carolmlMarch 14, 2012

In my new kitchen, I will put an induction cooktop on an island. I know that an overhead ventilation system is best but my CD keeps saying I should use a downdraft system to protect my view. If I was to do this, would there be any value in adding an overhead ceiling ventilation system. Currently, I have an industrial sized fan on the roof of the house that vents the existing cooktop. Could I redirect this so that I have a wide cieling vent near the cooktop powered by the existing extractor fan? I would use the downdraft while cooking but could clear the air in the whole kitchen afterwards. I expect that if I used them both at the same time, the overhead would interfere with the function of the downdraft. Is this a really dumb idea or could it be made to work? Thank you.

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kaseki

If you truly want to collect and remove the grease and odor instead of distributing it through your house, then you need an overhead hood that captures and contains the rising effluent. When close to the cooktop (30 - 36 inches, the size of the hood needs to overlap the pan surfaces such that the rising effluent, expanding at a 45-degree full angle, intercepts the hood aperture.

The simpler approximate rule is overlap the cooktop by 3 inches on each side. This may or may not provide full capture.

As the hood is raised higher, the expansion angle requirement causes the hood to get larger to be equally effective. Commercial hoods are typically 7 feet from the floor, and are proportionately larger in aperture area.

Depending on window design, ceiling height, and structure above the ceiling, a large capture area close to the ceiling might avoid much blockage or visual intrusion, capture adequately (if cross drafts are minimal), and allow you to use your existing roof fan.

I an convinced that an effective downdraft (really sidedraft ducted down) would have to pull enough cfm that the velocity could reach a m/s on the cooktop side opposite the vent to pull air across the cooktop. This is out of the question for any design that fits in the countertop, but could be achieved by a large duct aperture in a wall connected to a serious external fan.

MUA for this would add its own impracticalities.

kas

    Bookmark   March 15, 2012 at 11:57AM
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carolml

Thank you Kas for your detailed response. Perhaps I can still use the existing roof fan to power an over the cooktop canopy. It is quite powerful and relatively quiet because of the location.

    Bookmark   March 15, 2012 at 2:15PM
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beintruth

I had a downdraft and after several years couldn't wait to replace it. I actually replaced a working range to get rid of it. I too, never wanted to block my view into a wooded area but decided i needed good ventilation. Besides that when I put the downdraft on, (I have gas by the way) all the flames would be drawn to the downdraft and sometimes I would have to put the fire set to the highest setting just to saute. Was I surprised when I bought my Zephyr Milano with glass and stainless to help not loose the view. The entire ventilation hood did not in anyway obstruct my view at all. I had to laugh! All this time I could have had a island ventilation hood. It is so quiet another plus! Good luck!

    Bookmark   March 21, 2012 at 4:26PM
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beintruth

I am not able to have a ducted ventilation in my new condo. I will have a 30" induction cooktop and was told you don't need a large hood with induction cooktops as you do with regular gas or electric ranges?
The condo is situated in a very breezy area by the ocean.
Question: I am wondering if a ventless exhaust system is worth having and spending the money for. Do they really work well not being vented. It would also have to be over an island. I was told One great brand that uses a heppa filter doesn't do island hoods. I think it was vent a hood.
I don't deep fry but do love to cook.

    Bookmark   March 21, 2012 at 4:42PM
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carolml

I think I've always known I would need a proper hood fan but needed to explore the different options. I will just have to find a pretty one or one that I can see under, like yours beintruth. Still hoping I can use a remote blower to keep the noise down.

    Bookmark   March 22, 2012 at 12:38PM
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eleena

I have the same question as BEINTRUTH.

Looking forward to the expert advice. :-)

    Bookmark   March 22, 2012 at 2:55PM
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palimpsest

The Futuro Futuro Skylight ventilation fan can go flush in the ceiling if you have an attic above, or in a relatively flat soffit if you have a second story.

    Bookmark   March 22, 2012 at 3:11PM
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carolml

palimpsest - I have looked at this one, in fact this is what got me started on the idea of using my existing bower. I wonder how efficient it is being so far above the cook top? Does anyone actually have one?

    Bookmark   March 23, 2012 at 1:57PM
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kaseki

A hood that is relatively close to an 8-foot ceiling should be twice as wide and twice as long as a properly sized one at 30 inches over the stove, and have four times the air flow if flattish. If it is sufficiently peaked inside to where the air is collected (where the baffles are, requiring it to penetrate into the ceiling), maybe two times the airflow would be adequate.

MUA has to be proportionately increased.

kas

    Bookmark   March 23, 2012 at 2:26PM
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attofarad

Same issue (view) at my house. Even though I wanted to put the cooktop on the island , I ended up putting on a wall countertop to preserve my view.

A friend has a gas cooktop (modest by GW standards!) on his island, and uses a popup side/downdraft vent. It seems to work pretty well for him -- no meat sizzling, but lots of Indian spices at his house. He doesn't have the view issue, but has a high ceiling with a skylight over his island. It DOES look much better than a hood would.

    Bookmark   March 23, 2012 at 5:48PM
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maire_cate

I've had a popup/downdraft ventilation system on our island for 28 years and I have no complaints. We did it because we didn't want an overhead vent and and yes we use our kitchen - a lot. My first was a Thermador downdraft and gas cooktop. We updated the kitchen 6 years ago and installed a Dacor gas cooktop and pop up vent and remote blower.

We do stir fry occasionally and cook fish and we often sear steaks in a really hot cast iron skillet. My ceiling has not turned yellow from the rising grease.

As for pulling the flames from the pot - I haven't had that problem. The vent rises at least 10" so it's well above the flames.

Dacor had 2 different remote blowers. Ours is the 600 CFM since we have a short run but they also have a 1000 CFM and I think they now offer a 15" pop up.

We also have the same set up at our vacation home in the mountains.

While an overhead vent is the most efficient it isn't the only option. Perhaps if we had 23,000 burners it might make a difference but our Dacor is either 15,000 or 18,000.

    Bookmark   March 23, 2012 at 7:44PM
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