Air Filters

The air filter in your home’s furnace, air conditioner or heat pump is an important but often overlooked component of the HVAC system. Though they may seem like nothing more than cardboard boxes full of fibers or pleated material, air filters actually affect several crucial areas of indoor comfort and HVAC equipment performance. The continued high performance of a system begins with the air filter.

An air filter is usually made of a spun fiberglass material or from pleated paper or cloth enclosed in a cardboard frame. Its basic function is to clean the air that circulates through your heating and cooling system. Filters trap and hold many types of particulates and contaminants that could affect your health and comfort, including dust and dirt, pollen, mold and mold spores, fibers, lint, metal, plaster or wood particles, hair, animal fur, bacteria, and microorganisms.

Filtration usually occurs when expended air is brought back into the HVAC equipment to be conditioned and distributed again. The air is forced through the filter, and the material removes particulates and other contaminants from the air.

Filter efficiency and performance is often indicated by the filters’ minimum efficiency reporting value, or MERV rating. Standard MERV values range from 1 to 16, with the number serving as an indicator of how well the filter will remove material from the air. Higher MERV numbers indicate high levels of filtration.

For a residential setting, you will want to stick with a midrange MERV rating of 8-10. These filters provide good filtration and are commonly used in residential settings. They’re often made of pleated cloth or paper to provide more surfaces for capturing particles.

The higher-rated types of filters are highly effective (and cost more), but they’re also thick and dense and can interfere with airflow inside your home’s HVAC equipment. High-MERV filters can reduce your heating and cooling effectiveness and could damage your HVAC system by restricting airflow.

All of the air that heats or cools your home will eventually pass through the air filter in the HVAC system. For this reason, it’s extremely important that you keep clean filters in your heating or cooling equipment.

Dirty, clogged air filters are a primary source of HVAC system malfunctions. In the more extreme cases, dirty filters can damage heating and cooling equipment. Dirty air filters can reduce the airflow inside the HVAC system, which can cause air-handling fans to work harder and wear out quicker. Dirty air filters can’t remove particulates and contaminants effectively, which allows these materials back into your indoor air.

If you have a one-inch filter, it’s important to replace it every 30 days. A four-inch filter needs replacing once every 3-6 months. Electrostatic filters are replaced as needed.