Chapter 04

Air Filters: A Small Part with a Big Job

The air filter protects HVAC equipment by capturing some airborne particles before they reach sensitive components. A loaded or incorrectly fitted filter can restrict airflow. A filter that is too restrictive for the equipment may also cause airflow problems.

First, locate the filter. It may be in a return-air grille, at the indoor air handler, or in another location specified by the installer. Use the exact size and type recommended by the equipment manufacturer or HVAC professional. Note the airflow arrow on the filter frame and point it in the direction of airflow.

Inspect the filter regularly, especially during heavy-use months, when pets are present, or when construction creates extra dust. Replace or clean it according to the manufacturer's instructions and the conditions in the home. A calendar reminder is helpful, but the correct interval varies. Some filters are disposable; others are washable and must be completely dry before being reinstalled.

MERV is a rating of a filter's ability to capture particles under standardized test conditions. A higher number is not automatically the best choice for every system. Before changing to a higher-efficiency filter, ask whether the blower and filter cabinet can handle it without reducing airflow too much.

Never operate the system without the required filter. Do not stack filters or force an oversized filter into the slot. If the filter bows, leaves gaps, whistles, or is difficult to remove, ask a technician to check the filter rack and airflow.

A filter is not a cure for every indoor-air problem. Source control, moisture control, ventilation, housekeeping, and properly selected filtration all play roles. For unusual dust, odors, or persistent symptoms, investigate the source rather than simply buying a denser filter.