What cfan does the 4 series come with? The 3 series that came with my cooler was a Delta 21cfm fan. Your choice is slim. Delta 38cfm, Papst 31cfm if you can find. Y/S 26cfm or thier 21 cfm quiet fan. I settled for the two 26cfm units on the PEP66 before I converted to the 462A Swiftech.