We want to install a 1200 CFM (Best IQ) but are restricted to connecting through a 10" x 3.5" rectangular duct prior to an 8" round. So we know that 10x3.5 will choke it back but we want to know how bad the effects would be on the system.

We believe it to be a straight 35% reduction by calculating but don't know the effects to the unit - will it be substantially louder? Will the unit burn out because it has to work harder? Will we be voiding the warranty by installing it this way?

Has anyone else installed a vent in a similar fashion?

Additional details...from the hood to the ceiling is there the 10"x3.5" transition piece is. It creates a 90 degree turn in the ceiling and then connects with am 8" round. 8" round runs for 10', 90 degree turn again, 15' and out.

Thank you!