There isn't a perfect temp, other then below 75 F with below 50% humidity, 60-70 sounds good, but chins can handle much colder. Too cold is if the water freezes, but only because then they would have no water, lol, the lowest I've known chins to be in and survive was around 20 F (during a power outage in the winter). Chins can't sweat and are wearing a very thick fur coat, so very little to no heat loss on there bodies, if it's not too cold for you it's definitely not too cold for your chin.