Asked on: July 5, 2013 by Question via Facebook Is it more economical to turn the A/C up during the day and down at night, or leave it at the same temperature all day? The urban myth that you should leave your thermostat at the same temperature all the time has been around for decades. The truth is, it takes a lot of energy for your air conditioner to run all day, maintaining an inside temperature that’s significantly lower than the outside temperature. On the other hand, if you set your thermostat higher in the morning, the unit will run less during the day, saving you money on your FPL bill. Even if the air conditioner has to catch up when you bring the temperature back down later, it is still more economical to keep your thermostat set higher during the day. By the same logic, if you are in the habit of lowering the thermostat before bedtime because you prefer a cooler room while you sleep, your cooling costs increase by up to 5% for every degree you lower the temperature!