The frequency for changing air filters depends on the type and environment, but general recommendations are as follows:

• Vehicle cabin air filters should ideally be replaced twice a year, before and after the pollen season, to maintain air quality and avoid bacteria or mold buildup. Annual replacement is not sufficient for health reasons.

• Vehicle engine air filters typically need changing every 30,000 to 45,000 miles, but this varies with driving conditions and manufacturer guidance.

• Household HVAC air filters usually last between 3 to 12 months depending on filter thickness and usage. Thicker filters need less frequent replacement. Pet owners or dusty environments may require changing every 1 to 3 months.

In summary, for general household HVAC filters, changing every 3 months is a common guideline, but it should be adjusted based on environment and filter type. For car cabin filters, replace twice yearly for best air quality, and engine air filters around every 30,000-45,000 miles depending on conditions.