With the sudden local heat waves we have been experiencing you might have wondered: If you save energy by turning off your air conditioner when you are gone? Or would it make more sense to let it run at the same temperature setting all day long, so you don’t overwork your AC unit?

Let’s look at both options.

Keep it running:

This theory is founded in the thought that by keeping your home at a comfortable temperature all day your air conditioner won’t have to work as hard when you decide to turn it on after a hot day. It also assumes that the air conditioner might use more energy when it’s time to cool things down.

Turn it off:

Even if your air conditioner has to work harder to cool the house when you get home, that doesn’t waste more than letting the air conditioner run all day.

So what saves more energy? That all depends on how long you will be gone and how efficient your AC system is. The EPA says it’s better to shut off the air conditioner if you will be away for more than a few hours. If you’re just stepping out to do a quick errand, leave it running. But if you leave for an eight hour work day and have no pets in the house, shut it down. You will have energy savings by turning it off. While it may seem like your unit has to work hard to cool a space down from 88 to 78 degrees but it’s even more wasteful to keep it running for eight hours. However if you’re a/c has difficulty cooling off your home in an acceptable time that could be a telling sign that system is inadequate. Your system could have a host of problems such as leaky ducts, maintenance issues and more than likely have been installed wrong as 90% of systems are installed incorrectly. If this seems like the way your system responds in a heat wave you should hire a professional to inspect your system.

So is the energy saving worth coming home to a scorching hot house after a long day of work, even if your system is running smoothly? We also highly recommend investing in a programmable thermostat, which can let the house warm through the day, then gradually lowering it to the right level before you return. If you allow your house to become too hot you could also cause an extra load on your refrigerator and possibly melt chocolate or spoil produce.

U.S. Department of Energy suggests:

1. In summer, set your thermostat for 78°F (26°C) while you’re home, raise the setpoint when you’re sleeping or away from home.
2. winter, set the thermostat for 68°F (20°C) while you’re awake, and set it at energy-saving temperatures l for when you’re away or asleep.

Another option is a whole house fans. We installed a QuietCool whole house fan into our personal home and have seen considerable energy saving and enjoy bringing in the fresh Idyllwild mountain air in the evening. A whole house fan is usually installed in the attic and pulls fresh air into the house from open windows and exhausts it out the attic. Often, in warm climates like Southern California a whole house fan together with ceiling fans and open windows is enough to keep you comfortable at night. These fans should be installed by a professional though — and you always need to make sure you have enough ventilation in the attic once you have it installed. Otherwise, the fan could create a backdraft in your furnace, water heater or gas-fired dryer, pulling dangerous things like carbon monoxide into your home.