I keep a RES, a chicken turtle and 3 cooters outdoors in the Philadelphia suburbs. I only took them indoors 2 weeks ago. Temps were dropping to the 50's, high 40's, and I moved them to their indoor winter quarters in the basement. One of my cooters has been in my household for 31 years, and she was about 25 years old when I got her in 1978. I have kept turtles for 50 years now. They are very sturdy animals, and if you pay attention to them, you can tell when they need to get in out of the cold. When I bring them indoors, they really seem to know that they will be in the basement pond for a few months (till April, actually). They adjust to the seasonal change really well. I used to heat their 200 gallon indoor pond throughout the winter, but it got costly. They are now in water at about 55 to 65 degrees all winter, and they slow down a bit, eating about 25% of the amount they eat during the warmer months, but they thrive. If it gets TOO cool in the basement pond I run some hot/warm water into their environment, but, frankly they seem to do well in the cool water, eating less but staying rather active till spring. When I DO bring them out again in April, they seem to rejoice when reintroduced to the more natural environment. Sometimes I'll use supplemental heaters, both indoors and in the backyard pond, but basically, if you pay attention to them, they'll make their metabolic needs known by their behavior. I have learned by trial and error, but you can really tell by their behavior when they are adequately cared for, and when you have to punch it up a notch. Listen to them.