we live in So. CA, and are running 5 or 6 chillers. it really depends on what temp you keep your tank at, what your room ambient temp is, your tank's intrinsic temp, and what you're keeping. the place we're renting gets pretty warm, and we have one tank that we run at 63*F, and a couple more we run at 74*F, not to mention that we really don't like any of our setups to run warmer than 77*F.
as mentioned, only you can answer those questions.