Kitchen Fitting

Ducting for downdraft extractor

Anonymous user 1 March 2024 - 2.58 PM

I asked my builder to install ducting in the floor of our kitchen extension for a downdraft extractor. I told him that the extractor needs a 150mm circular duct or equivalent area rectangular duct. However my builder has installed a 100mm x 50mm duct in the floor and laid the final screed over it. My builder says he has always used this size duct with downdraft extractors and no one has had a problem. The length of duct is about 2.6m with one 90deg bend. So do people think a 100 x 50mm duct will be OK or should I insist it is replaced with a 220 x 90mm duct as recommended by most downdraft extractor manufacturers - Neff, Bosch, Elica with boost flow rates of 580m3 /h. Aside from telling me the 100 x 50 duct will work, my builder also says the 220 x 90 duct would need a mesh of rebar over it to prevent the screed cracking. How would others deal with this? Finally my builder has fitted a single air brick on the outside wall at the end of the duct. Is this big enough?