Originally Posted by shellieca
Well you've only had yours for 5 months, Bettas have lived without heaters but it doesn't mean its healthy for the fish or that the fish is happy. More often than not, a Betta not kept in water of the proper temp will not live as long as he or she should. If where you live is always 80F then you probably don't need a heater but I would at least get a thermometer to see the water temp.
My apartment is small and always pretty warm, and I've never seen him lethargic or looking unhappy in any way. Every single time I look at him he is swimming around happily and poking around in his plants. I'll probably end up getting one eventually, but for now I like to think he's happy without one. Plus the tank is only 3 gallons, keeps warm pretty easily just being in a warm environment.