ALL YOU HAVE TO DO IS KEEP PUR THEROMSTAT ON 75 DEGREES KEEP BLINDS AND DOORS CLOSED. AND YOUR HOUSE OR APARMENT WILL STAY COOL. THE MORE YOU TURN YOUR AIR ON AND OFF THE HIGHER THE LIGHT BILL IS GOING TO BE. AND ON THE VERY HOT DAYS USE A FAN TO CIRCULATE THE COOL AIR.I KNOW BECAUSE I'VE BEEN DOING IT SINCE APRIL AND MY LIGHT BILL HAS ONLY BEEN 100 DOLLARS A MONTH. THIS IS IN A HOUSE.