When it's 100 F outside you should aim to have the interior temperature at around 78 F at least.
However if you can get the house temperature to 68 or lower that would also be good.
But when it's really hot out it can be a struggle to get your AC to cool down your house below 78 F to 70 F.
The majority of air conditioning units are designed to only cool the air about 20 degrees from the outside temperature.
If the temperatures outside are approaching triple digits, you should set your thermostat at about 78°.
By setting your thermostat to no more than 20 degrees below the outside temperature, you can save on energy costs and help give your AC a break.
The next time it's hot and muggy outside, appreciate that your AC is doing its best to keep you a comfortable 20 degrees cooler.
Some ways to keep your house and yourself and family cool when it's 100 F or more outside include.
Keep your blinds closed.
Invest in blackout curtains.
Be smart about your doors.
Hack a fan instead of turning on the air-conditioning.
Set your ceiling fans to rotate counter-clockwise.
Focus on the temperature in your body, not the house.
Sleep low.
Let the night air in.
When indoor air temperatures are hotter than about 95 °F: Fan use may cause your body to gain heat instead of lose it.
On very hot, humid days, sweat evaporates off the skin slower than normal, and fans make it even more difficult for the body to lose heat by sweating.