Effectiveness is influenced by capacity of unit. If you are trying to mount a 270 cfm fan more than 30" above cooktop, then it may make noise but will do little to clear the air. If it is 1000 cfm, then it can be higher than 30". So the answer is "it depends". Most people don't mount them more than 36" above the cooktop unless it is a really high powered unit.

I had purchased hafele hob 10 months back... I got it serviced 6 times... Now i requested for replacement with new one... Still they have not attended my request...

Sophie, Patricia you are right cleaning the crystals would be a hell of a job. Hence I would like to look at designs like the other pic I attached which is I believe from the e.ion range of Falmec. As I have mentioned before this is a second chimney. The primary chimney hood is above my gas job in the kitchen countertop and is the main and daily area for cooking. This is the secondary area which I plan to use for some quick heating, occasional stir fry etc. The pendant chimneys that I have come across in brands like Elica and Falmec do not require ducting. The filter needs to be changed every 6 months or more. With my kind of usage I am assuming I would need to change it even later. What I am looking for is different brands which have pendant chimneys. Right now I am only aware of Elica and Falmec. I know Siemens and Bosch don't have it. Siemens has 2 models which are like a flat rectangular panel to be attached to the ceiling or false ceiling. But the cost is same as the Falmec chimney. My only respite may be the cylindrical Isola chimney models from Faber or even Hafele which are ip within budget.

@corner Stone designs. sorry if I had given an impression it mud slinging. but objectively speaking the suggestion to go for a chimney just because someone asked for it instead of addressing the real issue us not what I intended to do. one has to understand all the negatives as well veggie going in for a decision . just like you have the right to suggest there is nothing wrong in pointing out the issues in the proposed solution. none of us are internet warriors but most of us are "sold" items that we will never need in our life by creating an illusion. I know that dinner call it business but I am not in such one and I have the luxury to call a spade a spade. Even now the person who asked for is not sure in what they want but they think that a chimney will solve the issue. engineering doesn't work that way. unless we know what the real issue us, which isn't clear if it is the smoke or the smell and the your of food cooked, the frequency, the 80/20 utility of the kitchen we are not even close to understanding the problem. my intent is to emphasize the importance of understanding the problem and then look for issue and not provide a ready made solution. we can all suggest something by seeing a picture that fire will come and catch the chef if it is located in the window but do you think that what you say is practical. you may construct this as much slinging be as a novice I have a genuine question. how many houses have such a fire accident. we don't even know if the stove is electric or gas. if it is electric then they just no question of fire. so I encourage you to objectively approach and not see this as a mud slinging thing as that's not the point.