recommended temp for controlled climate for humans is 22 degrees centigrade (actually 20 for women and 24 for men, so they average it out so no-one is comfy. So I would probably aim for around 20 as an optimum. But, that would cost a fortune for the whole run. If you had a box within the run you could heat that to around 20 and the cat could choose where it wanted to be ... Alternately you could provide a warm sleeping pad and keep the general heat around 17 or slightly lower... THese are just thoughts, not expert opinions, by the way...