I was at PETSMART today... I almost bought a 2.5 gallon tank and a new Betta - but I stopped myself because I can't put a heater in that size tank. I've been bummed all day about not buying it.

You guys/gals here have taught me to do the right thing when it comes to Betta's, they have needs too. So I want to do the right thing.
I wonder if those of you who have the smaller tanks go without heaters.
Is this really okay? I have central air in my house so its cool in the summer inside the house. I would just hate to freeze a little fish.
Am I overreacting about no heater in a small tank??? My 10 gallon tanks obviously have heaters.
Thanks in advance for your opinions!