I haven't purchased yet. The 6" gives me 340 CFM which is more than enough for my needs. I'll dial it down to about 240 CFM with a controller - not included. I have to wire in a power cord. Cost is USD $156. I'm concerned with the noise and I'm hoping this fan will be pretty quiet.

Do you have a link to yours? I'd be interested to see. Have a look at the Panasonic here: Panasonic 340 CFM WhisperLine Inline Ventillation Fan for 6" Duct