Designing Kitchens and Bathrooms - how do I install fan in attic for kitchen range hood

we're moving into a new house which has a range hood installed but so far the ducting and exhaust for that unit is not installed. As the range hood is attractive stainless but as range hoods are generally very noisy and it is an open concept kitchen/great room, I want to install an in the attic axial flow fan using the existing fan hood, just not turning on the range hood fan to reduce noise. The Fantech model FG 6XL I think I should use is supposed to provide 300 cfm extraction. Should I install a separate backflow preventer or use one on the range hood? Should the vent pipe go as vertical as possible in the attic space up to the roof vent? The range hood evidently has 4 inch ducting but the attic fan only comes in 6 and 8 inch duct sizes. Which size would be best? Any comments on the plan would be appreciated.

Dampers should always be used to cut down on cold air back drafts. But make sure the fan is approved for venting a cooking space. Accumulation of cooking grease, etc., can be a major problem over time. I like Fantech for bathrooms or other spaces, but not sure it is rated for kitchens.

Welcome to the forums! The Fantech site had a wealth of information, including PDF files for all their stuff. I would go with their recommendations, regarding vertical or horizontal installation. I am not a big fan of cutting a hole in a perfectly good non leaking roof, so I would opt for a wall or soffit exit for the fan. Will the area you plan on installing it in be accessible for a change out at a later date? I have never seen a kitchen range hood with only a 4" duct, but that is not to say they aren't out there. I would to with no less than the 6". Properly installed at the far end, the closure means to the ducting whether it is a dryer type vent or soffit vent will provide back flow prevention, but is could be a concern if you run it out the roof, as the cold air dropping down will certainly need help to keep it out of your kitchen. Here, again, Fantech has all those parts, so search their site, as I am sure you will come up with a good solution. Let us know if we can help further.

Fantech is a very good fan for your application.

Fantech and American Aldes both have gasketed duct dampers that work much better than the average box store variety. A good place to install them is where the temps change from house side to attic side at the attic insulation (this minimizes thermal/convective loops wasting energy).

Like chandler, I try to minimize roof penetrations, but done properly a roof vent is OK. Definitely the 6" duct (don't need bigger).