How do you choose the right size and type of air filter for your HVAC system (and how often should you replace it)?

To choose the right size and type of air filter for your HVAC system, first check your existing filter for size markings, often indicated as length x width x thickness (e.g., 20x25x1). If unclear, measure the dimensions manually and round to the nearest inch for the nominal size, keeping in mind that actual dimensions are usually 0.25 to 0.5 inches smaller^[1].

For filter types, MERV ratings indicate effectiveness, with higher numbers capturing smaller particles but potentially restricting airflow^[2]