Hello,
We just bought a new Neff cooker hood/extractor fan and I am trying to buy the correct ducting to ensure we don't limit the performance of the fan. I have gone for 150mm cylindrical plastic ducting (as recommended by manufacturer). On the outside of our kitchen I need to install some form of weatherproof outlet (very windy where we are). So I have gone for a 150mm cowled vent (see attached picture). Simple right? Only now I have bought the vent I see that the inlet is cylindrical 150mm in diameter (i.e. 17600 mm2 in area) but the outlet is a rectangle and only 80mm by 150mm (i.e. 12000mm2). That means the cross section of the outlet is only 68% of the size of the main 150mm ducting. Won't that create quite a bit of back pressure and reduce performance? Any ideas welcome? Can you buy cowled vents which have bigger openings (they don't seem to be specified by suppliers). Are there other solutions?
Thanks
AP