What typically happens to filter efficiency as dirt accumulates?

As dirt accumulates on an air filter, filter efficiency typically decreases. This is because a clogged filter can obstruct airflow, making it more difficult for air to pass through. As a result, the filter may not capture particles as effectively if the dirt buildup impedes the filter's ability to function optimally. Over time, the decrease in efficiency can lead to increased pressure drops, ultimately straining the HVAC system and reducing its overall performance.

While it's true that some filters can initially see a slight increase in efficiency as particles catch in the filter media, effectively reducing the size of openings and trapping additional particles, this is not sustainable. Continual accumulation of dirt will eventually hinder airflow to such an extent that the filter becomes ineffective, leading to a decrease in overall efficiency.

The other options do not accurately represent the typical behavior of air filters as they collect dirt, as filters do not usually maintain constant efficiency, dramatically increase efficiency, or show erratic performance in a predictable process.