It's just like radiators in houses years ago. Somehow the dogs and cats knew better. When I was little, our cat use to sleep on it in the summer, somehow in the winter it knew to stay off it. I have a oil filled heater in our house now that we use in the winter (danged old houses never heat and cool right), the cats don't bother it.
Another a separate note, we have a number of fans in our house now to help circulate cool air in the summer. One is a big box fan that sets on the floor. One of the cats loves to sleep behind it when it is running. Not in front of it, behind it; never figured that one out.