When is the best time to run the air conditioner?

Talk with your HVAC specialist to determine the best solution for your coolant problems. (Photo courtesy of Angie's List member Robert N., Berea, Ohio)

Talk with your HVAC specialist to determine the best solution for your coolant problems. (Photo courtesy of Angie's List member Robert N., Berea, Ohio)

Dear Angie: What is best way to run air conditioning? Is it better to keep the A/C running all day at, say, 75 degrees? Or should I turn it off all day and then when I come home from work, turn it on? Is one more expensive than the other? – Sandy M., Battlement Mesa, Colo.

Dear Sandy: Air conditioners are designed to maintain a constant temperature in the home, so it’s best to let it run and maintain those even temperatures, than to try to catch up. The cooler you can keep the house, the less the unit has to work.

The ideal way to run your air conditioner is to have a programmable digital thermostat. You can set it to a desired temperature based on the time of day and even the day of the week. With this “setback” method, you want to keep your setback temperature and comfort temperature within five degrees of each other. So, for example, you can have the thermostat programmed to run automatically at 80 degrees during the day while you’re at work and then have it set to drop to 75 degrees just before you return home. That will maintain a comfortable indoor air temperature and save money on your energy bills.

Another relatively new product to help control your indoor air temperature is a Wi-Fi thermostat, which you can control online from any Internet-connected device – like a computer or smartphone – and can adjust anytime you choose.

You should avoid a setback variance of more than 5 degrees, or turning the air conditioner off before you leave and on again when you return. The problem with that is the system will have a hard time catching up to reach that desired temperature, especially if it’s an extra-hot day. The unit will work much harder to satisfy the thermostat setting, which will require more energy and ultimately defeat the cost-savings goal. By letting the unit run, it will cost less overall to operate and your home will almost certainly be more comfortable.

Whether you turn the unit off and on, or run it all day, it likely won’t damage your A/C, provided it’s in good shape and maintained on a regular basis. Most reputable heating and cooling specialists offer low-cost preventative maintenance programs to keep your system in good working order. A good heating and cooling contractor can also offer advice on the best way to keep your home comfortable and energy efficient. Of course, one simple but important way to keep your system working well is to inspect and change your air filters regularly.

Angie’s List collects about 65,000 consumer reviews each month covering more than 550 home and health services. Angie Hicks compiles the best advice from the most highly rated service pros on Angie’s List to answer your questions. Ask Angie your question at askangie@angieslist.com

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Is closing the vents in rooms that are not used make for better cool air flow in rooms that are used all the time. Doors to unused rooms are closed.

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