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 turn it on when I come home from work? 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 better 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 5 degrees of each other. So, for example, you can have the thermostat programmed to run automatically at 80 degrees 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 — such as a computer or smartphone — and can adjust any time 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 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 probably won't damage your A/C, provided it's in good shape and maintained regularly. Most reputable heating and cooling specialists offer low-cost preventive maintenance programs to keep your system in good working order. A good heating and cooling contractor also can offer advice on the best way to keep your home comfortable and energy efficient.
One simple but important way to keep your system working well is to inspect and change the air filters regularly.