A bar owner asked me to move some exhaust grills for her. The bar has a suspended ceiling. From the bottom of the exhaust system metal duct at the true ceiling are 3 16" flex ducts coming straight down about 3' to 3 side-by-side grills. She wants me to move 2 of the grills to other areas of the bar. I would have to extend the ducts about 15'-20' to evenly distribute the exhaust grills throughout the bar. Does anyone see extending the ducts that long creating a problem for the exhaust?