Hey Bama. Yeah your guy should not need a heater. They are pretty tough fish, just remember to cut down on the amount of food you feed him if it's really cold. "Really cold" to a betta is under 65, so as long as he at "room temp" you should be OK. Putting a heater in a container that small would prob cause more probs than it would solve.
BTW, I've kept and bred bettas for years, even have a few awards for 'em from the local trop fish society.