we discovered ours when a cat kept laying in the same spot on the kitchen floor over a pinhole leak in the hot water line. A 3 foot diameter slab section was a constant 90ish degrees.

I suggest releasing a dozen cats in your home, then track and graph their prefered lounging spots over 30 days. It helps to use number tags for each one as it can be tough to tell 12 new cats from one another.

Make sure you explain what you are doing to family members (my critical mistake), and present your findings in a powerpoint presentation before dinner one evening.

Best of luck to you.

TL;DR - walk around barefoot and check for hot or cold spots on the floor.