Can anyone chime in on this please? I really need to decide it fast. I'd be most grateful to hear some thoughts on this. Thanks!

You cannot vent a cooking appliances into a chimney. That would be a fire hazard. The other is substandard as well. Engage a HVAC professional to look at your issues.

If the chimney isn't used by anything else (non existent fireplace), why can't it be used for venting a rangehood?

What is your builder saying?

Well the chimney is not being used by a fireplace or anything else and it won't be ever used for anything other than the range hood. So I think it's good to go, but what concerns me the most is the 6 meters horizontal duct till it comes to the chimney. Then the chimney is 7 meters high, but I suppose the natural airflow will take the hot air out as soon as it gets to the chimney. But those 6 meters horizontal duct is whats bothering me. What do you think about it?

I recall that the installation instructions for my range hood fan had specifications about the duct. I agree that you need a professional to have an opinion.

You are quite right to be concerned about the 90 degree turns and the length of the run. I have no knowledge about fire hazard, but what will happen if the air flow is not short and straight, is that the fan will simply not work. It will not pull the air out the way you want it to. Don't install until you are sure.

It's the microscopic grease particulate accumulation inside the chimney that makes it undoable. You would need to line the chimney with smooth metal duct, and increase the CFM of the fan, as well as the capture and filtration area over the cooking zone.

You really need a Pro here. You aren't understanding the possibilities and the potential health and safety ramifications of your decisions.

I found this which gives a calculation of how strong your fan needs to be. In addition to the size of the stove, a longer length of pipe and more bends means that you need a stronger fan. http://www.todayshomeowner.com/how-to-calculate-kitchen-range-hood-fan-size/

For every turn the duct work makes the higher CFM your hood needs to have a 6m run is way too long anyway. The grease will cool before exit and stay in there. I agree I would get an expert in to do this .

Sounds like you need to move the range.

Without the heat of a fire, there is nothing to push the air up the chimney and out. It is not an acceptable vent.

Okay guys thanks for the awesome recommendations. I will see if I can drill the upper wall and go outside the roof directly above the hood. It should be the best solution of all.

Just so long as you understand, that several of us have advised you to get professional advice in your house, before starting work.

Yes I am trying to actually, but I reside in a small town and most of the professionals are the "jack of all trades, master of none" type, so they suggest different kind of stuff. Some say chimney is ok, others say 10 degree downwards is fine, but they don't seem to have much experience with such cases to be trusted, or at least that's what I think based on their varied opinions.

Do you have a photo of the wall where your range is, the chimney is, and where the window is? It's very hard for Houzzers to visualise otherwise.

Here is the direct view of where the hood is going to be installed and the two options illustrated with colors.There goes the duct to the chimneyAnd here it is where the duct will connect into the chimney. The navy blue big dot represents where a hole will be drilled. The navy blue arrows represent the direction of the chimney behind that wall.

Sorry about the amateurish mockup, I hope my photoshop skills are good enough to give you a picture of the situations. :)

I haven't tried contacting them. Gorenje is my manufacturer for the hood. I will give them a call today and see what they will say. The instructions that came with the hood are very clear that the duct should either get out right behind on the outside wall or up through the roof directly vertically directly above the hood. No other scenario has been mentioned in it whatsoever.

No one has said that the 10 degree slope would be a problem, but I was a bit concerned since hot grease might get trapped in there or something. I would really like to hear anyone's advice on this 10 degree slope before I begin drilling up to get out to the roof. I really don't want to make holes that big for a range hood.

I know they are nowhere near as effective but is there a possibility that your rangehood could be changed to a recirculating rangehood, where you use replaceable charcoal filters - no venting to outside required.

My range is on an external wall. The hood has a very short pipe.

I've decided to go up through the roof. It was not the most elegant solution, but since the chimney option was not gladly accepted by most of you guys, and I was afraid going down below the lintel so I can avoid grease accumulation in the duct(I was also afraid of noise from outside) it was the safest one to go with. Thanks to all of you for your opinions!