It's natural to leave the air conditioner on for your cats when you leave home during Japan's humid summers to prevent heatstroke, but don't you still worry a bit?
The room I used to live in was warm and comfortable in winter, but very hot in summer, and I was genuinely worried when I left my cat alone.
I remember setting the room temperature low and directing a circulator towards the ceiling...
But when I came home, they were usually in hot places like inside the closet or on the bay window, intentionally choosing those spots...
Sunbathing is an essential behavior for cats, and they certainly tend to tolerate heat better than dogs.
They bask in the sun until they've had enough, then cool down in a chilly spot when they get too hot. It's just like a sauna.
Furthermore, they really dislike having air conditioning or fan air blowing directly on them, and when the air conditioner is on, they scatter to places where the wind doesn't hit them.
However, this doesn't mean you shouldn't take measures against heatstroke!
In fact, some cats do suffer from indoor heatstroke.
The recommendation is to create both warm and cool areas so your cat can regulate their own body temperature.
Set the air conditioner to a comfortable temperature for humans, and if you prepare beds in two locations—one cool but out of the direct airflow, and one warm in the sun—your cat will choose where to rest.
However, cats have a habit of periodically changing their sleeping spots, so always observe if they find new favorite places.
Also, senior cats, like humans, can have diminished temperature sensing abilities. To prevent heatstroke from occurring before you notice it, try to arrange your room so they can easily move to a cool spot nearby.