Hamsters can't blow electric fans, so I put a cloth on the cage, okay?

This will be hotter. The wind blowing outside was blocked by the cloth. You can put the cage in a dark corner, preferably on the corner of the ground and by the window at night. It will be cooler this way. You don't have to use sawdust in summer. It's very hot. Buy a sand mat for the mouse, or buy a small piece of iron to enjoy the cool.