If the fan is at the hood, then a silencer would help, possibly greatly help. I see no reason why the hood warranty would be affected other than the hood manufacturer covering its posterior against everything. The silencers from [US] Fantech have minimal restriction when matched to the duct diameter. Also, depending on the legal climate, the neighbor has a duty to not significantly pollute your environment. Reducing noise should be his higher priority than maintaining the hood warranty, particularly considering that the cost risk is limited to a blower. Perhaps more explanation about the 2-meter limitation would also help. Is this a neighborhood visual limitation? Height might move the apparent sound source to a better location, and in general the sound pressure level will drop in inverse relation to distance. However, given logarithmic hearing response, a significant distance might be needed for an apparent signficant reduction. It will take a heroic carbon filter to remove odor from a serious frying or grilling exercise. This is why outdoor ducting is usually embraced, to remove the odor (and grease particles too small to collect at the baffles) to the external environment. They have to be released high enough to not easily propagate to neighbors' houses. An upblast blower on a roof usually accomplishes this, and is the design most used by restaurants in the US. Often having a larger blade diameter than the duct size on which they are mounted, upblast blowers will generate less tip turbulence noise than a small diameter blower would for the same flow rate. kas

I wouldn't get a cheap hood. If you are spending enough money to do the thing in stone you should spend the money on good innards. It's called a "hood liner". Vent-a-hood makes them, as do other companies.

My bath has no fan & I do fine by cracking a window just a bit. Helps that I live alone & have no need to shut the door during a bath or shower. I also like having a floor fan running in the hall just outside the bath. This is really only necessary during the cold, winter months. Any other time, I just open the windows! I guess I just don't want to have to cut into the plaster & make a hole in my brick for a vent.

I'd love to be able to avoid that 90 degree angle... but the wall behind the range is concrete (and attached to someone else's home). So the exit location here I think is pretty much where it must be. Thank you for the input!