How often should residential HVAC systems be cleaned?

Frequency of cleaning depends on several factors, not the least of which is the preference of the homeowner. Some of the things that may lead a homeowner to consider more frequent cleaning include:
smokers in the household
pets that shed high amounts of hair and dander
water contamination or damage to the home or HVAC system
residents with allergies or asthma who might benefit from a reduction in the amount of indoor air pollutants in the home’s HVAC system
after home renovations or remodeling
prior to occupancy of a new home.