Why and How to Use a Timer

There's no need to blast the AC while you're away. For central units, install a programmable thermostat that lets you set higher temps when you're gone and cooler temps when you're home. Newer window units have built-in timers and adjustable thermostats, or you can buy a timer at any home store for $10 to $20; just make sure it matches your device's voltage. Unless you're going on vacation, don't shut off the system; otherwise, the air compressor will need to work harder to cool your house later.

Why and How to Fix Duct Leaks

Ducts can lose up to 30 percent of airflow through leaks. Find leaks using the old "smoke trick": For window units, light a stick of incense and hold it where the unit and the window frame meet; for central AC, hold the stick near duct connections. If the smoke blows around, you've got leakage. For ductwork, use foil tape to seal small gaps and duct mastic for larger ones; for window AC units, stuff foam between the device and the window frame, taping as needed.