The importance of hood installation is often overlooked. Using a underqualified installer could lead to improper reinstallation and cripple your ventilation hoods total suction and performance. If the ventilation hood calls out for an 8 inch diameter pipe and your installer uses a 7 inch diameter pipe you will have a 24 % reduction in suction. If your ventilation hood calls out for a 8 inch diameter pipe and your installer reduces the diameter to a 6 inch size anywhere in the duct run you will have a 44 % loss of suction. Kitchenfoundry.com is the leader in installation and specification . (949) 275-4496