Do All AC Units Have Two Filters

6February 2024

Do All AC Units Have Two Filters? Understanding Your System

When it comes to maintaining a comfortable and healthy home environment, one of the key components is the air conditioning (AC) unit.

A crucial aspect of AC maintenance that often puzzles homeowners is the air filter — specifically, how many filters are there, and where are they located? Common questions include,

“Do all AC units have two filters?” and “How often should these filters be replaced or cleaned?” This blog post aims to shed light on these queries and more.

The Role of AC Filters

Before diving into the specifics of AC filters, it’s essential to understand their purpose.

AC filters are designed to trap dust, pollen, pet dander, and other airborne particles, preventing them from circulating through your home.

Not only do they improve indoor air quality, but they also protect the AC unit’s components, ensuring it runs efficiently and extends its lifespan.

Single vs. Multiple Filter Systems

The configuration of AC filters varies widely depending on the type of system you have:

  • Single-Filter Systems: Most residential AC units are equipped with one main filter. This is typically located at the return air intake, which might be a central location in your home or within individual return vents in each room.
  • Multiple-Filter Systems: Larger or more complex AC systems, such as those found in commercial buildings or homes with advanced HVAC setups, may have additional filters.

These can be found at various points, including the air handler unit and each air return vent. Systems designed for high-efficiency air filtration might also employ pre-filters and HEPA filters to achieve superior air quality.

  • Special Configurations: Portable or window AC units usually come with a single, easily accessible filter.

Meanwhile, ductless mini-split systems feature a filter in each indoor unit, meaning a home with several indoor units will have multiple filters within the same system.

Navigating Your AC Unit’s Filter Requirements

Understanding your specific AC unit’s filter setup is crucial for effective maintenance. Here are some tips to guide you:

  1. Consult the Owner’s Manual: This should be your first step. The manual will provide detailed information on the number of filters, their locations, and maintenance recommendations.
  2. Regular Maintenance is Key: Regardless of the number of filters, regular checks are essential. Replace or clean filters (based on manufacturer recommendations) every 30 to 90 days, or more frequently if you have pets, allergies, or a dusty environment.
  3. Professional Advice: If you’re unsure about your system’s requirements or how to properly maintain it, don’t hesitate to seek advice from HVAC professionals. They can offer personalized recommendations and even demonstrate how to replace or clean filters.


The question of whether all AC units have two filters doesn’t have a one-size-fits-all answer.

The design and requirements of AC systems vary, making it crucial for homeowners to understand their specific setup.

By staying informed about your AC unit’s filter configuration and adhering to regular maintenance schedules, you can ensure your system operates efficiently, prolong its lifespan, and maintain a healthier indoor air quality.

Remember, the filters are your first line of defense against airborne pollutants. Keeping them clean is not just about maintaining your AC unit; it’s about protecting your home’s overall air quality and comfort.

Always point the arrow on the box in the direction of airflow. If you are unsure the direction of airflow turn on the system fan. Do not remove the old filter before checking airflow as this might allow dirt or debris to escape.