There are several factors in play here. How old is your home? Is it insulated? Do you have A/C that you run during summer months?
My tank can not live without a chiller, it just can't. My house heats up really bad in summer, and the swamp cooler just does not cut it.
If your house says cool during the hotter months, then a fan should work fine. If you live in an older home, with no A/C and the house is hotter than the outside temp, you need a chiller.