Extend exhaust flex duct
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?
if you do not have someone properly calculate ductwork, you will see what i often see in caffe bars: stains around few grills closest to exhaust fans, while the others are clear. meaning, only few grilles actually do the exhaust, the others are dead-laying. meaning ventilation efficiency can easily come to close to zero.
if exhaust worked properly right now, you might have good chance by making extension duct out of rigid ductwork that has much lower friction resistance.