The answer to 'when to replace air filter' is that you should replace your HVAC air filter every 1-3 months, or as recommended by the manufacturer. Air filters trap dust, dirt, and other airborne particles that can clog the system and reduce efficiency. Replacing the filter regularly helps maintain proper airflow and keeps your HVAC system running at its best.
The exact replacement schedule will depend on factors like the type of filter, the size of your home, how many people live there, and how much the system is used. Homes with pets, more occupants, or high dust/pollen levels may need more frequent filter changes. Checking and replacing the filter as needed is an important part of HVAC maintenance to ensure good indoor air quality and system performance.