Woah woah woah. Okay guys. Time to clarify this for both Floridians and non-Floridians.
Just because we live in Florida doesn't mean it's hot. On average, from what I have noticed, home temperature stays at around 72-78 degrees during the summer. The water in your tank will be a few degrees colder than room temperature regardless of how hot (or cold) it is outside.
Whether you live in Florida or not, a good heater is essential. Some bettas aren't as tolerant of fluctuating temperatures even if it IS only a couple degrees. Once winter hits in Florida (blistering cold, imagine breathing ice instead of water) then your tank could really DROP a few degrees.
So whether you live in Florida, or you don't live in Florida, whether you're in Florida or not, you need a stable, adjustable heater on your tank. >_> Especially if your betta gets sick and you find the need to bump up the temp a few degrees to help metabolism. Or your betta gets too cold from "room-temperature" water and gets lethargic, stops eating, and dies.
Just clearing up that misconception.