Is a filter required on HVAC duct connected systems for air intake?

In HVAC systems, a filter serves an essential function in maintaining indoor air quality and system efficiency. While it is not always mandated to have a filter in every duct-connected air intake system, its absence can lead to significant issues. Without a filter, dust and debris can enter the system, leading to blockages, particularly of the evaporator coil. This blockage can reduce airflow, causing the system to work harder and eventually leading to more expensive repairs or replacements.

Thus, while it's possible to operate certain systems without a filter, doing so can result in detrimental consequences for the HVAC equipment and the quality of the air being circulated in the living space. This context highlights the importance of having a filter, not just for regulatory compliance, but for the overall health of the system and the indoor environment.