We have central heating and air conditioning right now.  We keep our
temps at around 68 degree F in the winter and about 70-72 degrees F
during the summer.  Our fuzzies don't seem to mind the temps at all.
 
When we lived in Washington State we did not have central air but used a
lot of fans with the windows open (when the our ferret wasn't out) and it
got between 70-80 degrees (depending on the day, Seattle area weather is
slightly strange) and he didn't seem to have too many problems, obviously
on the days that is got really hot we made sure that his water was
changed frequently to keep it cool and we would give him an ice cube to
play with (both for drinking and to roll in the coolness).  Yes, melting
ice cubes make messes but...it isn't nearly as bad as the poop in the
corner. :)
 
We have also taking them outside to play in the snow when it is 30
degrees F out.
 
It is a matter of watching them to see their reactions and using common
sense.  If you are freezing, they probably are coming close, if you are
swealtering (frying) then there is a good chance they could be to.
 
Stephanie
[Posted in FML issue 4130]