Actually you want the fans blowing on the encaps because that's where most of the heat is produced. And yes, if you do go with the higher output kits you do want to cool them in order for them to run more efficiently. Whether you need them or not is really all dependant on what you want to keep in your tank and where. According to the guys at reefgeek, even if you go with the better kit which is the LET kit with the IceCap ballasts you'll still have to be selective on where you place things like sps and clams if you wish to keep those in a 24" tank.