I live on the second floor in an apartment building in Boston and I keep heaters in all of my tanks. I don't like the idea of large temperature fluctuations and have them set pretty low. But they will kick in when the temperature reaches something like 68 degrees. I think heaters, in the winter, are vital unless you can predict the temperature of the room consistently. Same reason you keep a thermometer in the tank. If you're not worried about temperature fluctuations, then why care record it? If there is a possibility then why not add a heater, set it on low, just to be safe? I have a thermometer in the room and the temperature there drops to 10 degrees (centigrade) every once in a while.