Riley is just constantly hot, even in winter. During summer he was constantly laying on the vents. And in winter he'll sprint outside and dive head first into a snow pile. I think that's it, because I use a harness with him, so that can't be much different in comfort than a sweater is, I'd think.
Also, he's a dude dog. Dude dogs shouldn't wear sweaters.
Dude dogs wear letter jackets!