Changing the air filter in your home's heating and cooling system is an important step to having healthy air in your home. It also keeps your system performing more efficiently. A dirty filter can make an HVAC system work harder, which means more energy use and a higher utility bill. To help you remember when to replace your filter and what size your unit needs, register for a free MyLowe's account at lowes.com. The program automatically keeps track of your purchases for you, so there's no guessing when it's time to change out your filter.