Air conditioner. There are a number of environmental, construction, and other things that supposedly reduce the need for air conditioning though. I can vouch for insulation.

The house I currently live in somehow was build with only partial insulation and it’s awful year round. My grandpa’s house was build with thicker than normal walls and full insulation and it’s perfect in even the hottest and coldest weather where I’d be mostly dead at home, and with heating only and no air conditioning.