Our house is relatively cool all year round (earth-sheltered, so it maintains a cool temp in the summer) and we have concrete floors that the dogs can choose to lay on if they get too hot on their beds. In the winter it's usually 62-72 downstairs (wood heat, hence the fluctuation during the day as the fire warms the house) and 72-74 upstairs. Sometimes Niko will pant as if he's too warm upstairs at night in his crate.
I know when we visit my parents house, which is always at least 72 degrees, and often warmer, both dogs but especially Niko will pant more, but that could be excitement too.
I think as long as your dog has access to water all the time and possibly somewhere to lay down that isn't carpet, he should be able to handle at least 75 degrees okay. Not sure about 80. You'll be able to tell if he's not handling it well.
Niko: American Showline GSD 5 years old
Rosa: American Muppet Dog (GSD/Border Collie mix) 5 years old