Hood used in the extraction, I was disappointed and surprised that he misses the check valve in the package. this information is missing from the product description. after a long search I found a dealer who informed me order one. I think this piece of a modest cost should be automatic in this kind of product. Suction capacity a little "just" (500 m3 / h?) But relatively effective. replacing an existing fan, I have not had any big problem in adapting the old housing.