Understanding the Relationship Between the Furnace Filter and Airflow

The effectiveness of your furnace filter and airflow are two competing interests inside your heating system. Airflow is a major factor in both the efficiency and performance of your furnace. A careful balance must be maintained between the need for adequate airflow capacity and the requirement for proper filtration. This is accomplished by selecting the right filter for your household and changing the filter regularly.

Filters are rated by their MERV (minimum efficiency reporting value), which ranges from 1 to 20. The larger the MERV number, the more efficient the filter. In most cases, airflow restriction also rises as the MERV number increases.

• Panel filters rated 1 to 4 on the MERV scale are the least efficient and restrict system airflow the least. Most contain fiberglass filter media and remove only the largest inorganic particulates of dust. The main purpose of these filters is to prevent wear and tear on heating and cooling components from dust and dirt. Because they don’t remove smaller airborne contaminants such as pollen, mold spores and bacteria, these filters may not have much beneficial effect on indoor air quality.

• Pleated filters made of cotton or fabrics like polyester occupy the mid-range on the MERV scale, from 5 to 13. These filters offer the best compromise between airflow restriction and particle removal. Pleated filters at the upper end of the range will remove 90 percent of inorganic and organic contaminants down to a size as small as 1.0 microns, including most bacteria, mold and pollen, as well as all dust.

• HEPA (high-efficiency particle arresting) filters are at the top of the MERV range. Normally used in hospitals and health facilities, these filters remove over 99 percent of contaminants down to .30 microns. Though HEPA is the gold standard for indoor air quality, the substantial airflow restriction usually makes them unsuitable for in-duct residential HVAC systems unless they’re installed in a bypass loop.

For more information about the important balance between an effective furnace filter and airflow, contact the team at Sobieski Services.

Our goal is to help educate our customers in Delaware, Pennsylvania, Maryland and New Jersey about energy and home comfort issues (specific to HVAC & plumbing systems).

Image Credit: gem fountain