Success with no heaters whatsoever depends on three factors.
1. What part of the world you live in. For example warm climates less of a problem than cold climates.
2. Ambient room temperature. Instead of heaters in the tank, warm the room up instead. This needs to be done in cooler climates.
3. And lastly, the actual fish you are housing.
Me, being from the uk? We have a cooler climate than most, i'm not prepared to fork out the heating cost for keeping rooms warm, as opposed to individual tanks, and I have tropical fish, most of which wouldn't do too well if the water temp was in the high 50's to low 60's.
No heaters for me would spell the end of my hobby, unless I went coldwater in fish choice.