No one cares for your family more than you do. You put their health and safety above all else. You’re careful to child-proof the home and check the carbon monoxide detectors. You make sure to teach your children about safety and hygiene. But you may be overlooking the most important thing. The air your loved ones are breathing can be contaminated and full of bacteria.. Proper cleaning and preventative maintenance of your unit ensures that mold, fungi and bacteria don’t get a chance to grow. HVAC experts recommend cleaning residential systems at least once a year.