Ok, several people told you to get a quality inline fan, and they are correct. Your 60 cfm fan is a duct booster I pressume? These are useless for growing pot. They have no ability against restriction as previously stated. Go to a growshop and ask for a 4" inline fan. It should be rated between 140-200 cfm, and will be around the size of a small basketball for kids. Grow shop brands worth a crap are Ellicient, canfan, vortex, soler & palau, and windtunnel. The s&p mixvent series are a good value though aren't as silent as some may have you believe. Those and windtunnel seem to be quietest. Use insulated duct to connect ad this lowers radiant heat and noise. P/c fans are crap for all but the smallest cabs. You need a 4" inlet some where for the cooltube. It does not have to be at the bottom. You need a 4" outlet for the cooltube. This should be as far from inlet as possible. This does not get rid of your heat problem. You need an inlet or two at the bottom of the cab that are light proofed, and preferably screened. An outlet to exhaust heat from within cab should be located up high, and needs to be run by a seperate fan, most likely a 4" one. This fan should suck from a carbon filter located up high to eliminate odor. That 2.5" hole needs to get a cool sticker or some tape covering it. If the room the cab is in is small or uncooled, heat may recitculate through cab and over time raise temps too high. Good luck.
