Texas cichlids (introduced not native) live in the City Park in New Orleans. Average winter temps there are in the 40's... so it's safe to say that they'll do fine without a heater. They're tough fish.
I've kept and bred by H. carpintis and H. cyanoguttatus in unheated tanks in my fishroom (avg. winter temps in the low 60s).
my texas goes from 52 degrees to 85 in my native tank, no heater. the 85 is only for a week or two towards the end of summer. the 52 is after a water change and gradually warms up to about 65 in the middle of winter.
in mine she starts getting frisky when the water gets into the lower 70's.
I am really glad I saw this! I was looking for this info because I was just given a sick Carpintus I am trying to nurse back to health, and I want to put it with my sunfish eventually.