I dont know where you live but here in Pensacola, Fl I lost ALOT last winter due to false info given to me. I lost 2 13" and 2 7" I thought I lost another 13" he was stiff as a board, I took him out and started to walk him to the garbage can, and thought hmm... and took him inside and filled up the sink with warm water and put him in. Then after a min or two I thought how stupid of me... and walked off. Then I herd a splash when I walked back by! HE CAME BACK TO LIFE ON ME! Not saying it will happen to everyone though... lol.
I bring mine in for the winter. When ever I hear someone at a petstore say yeah they do fine during the winter in the pond, I always tell them that they HAVE to watch out. But yeah if you have tanks in the house just put them in there.