Hi MIKE, if going into the wall or window direct then SIZE MATTERS!, the bigger the better!
however if going into smallish duct then use a centrifugal (drum) type rather than an impeller (FAN) type as more pull through upstream filters, also if duct longer than abt 1 mtr it needs to be insulated or cooking oil/fat will condense/ congeal -yuck! on inside of duct!, fit drain point or slope duct down to out side! regards SPARX
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