Furnace Filter Airflow Resistance

Merv filter ratings and air quality.

Furnace filter airflow resistance.

Likewise the mid merv filters also showed decreased air flow relative to the low merv filters this time 3 and 8 lower in the two systems. If your filter is either too dirty or too resistant it can cause airflow problems hurting the efficiency and performance. If you want your air to at least be cleaned and handle dust mold pollen and bacteria then a merv 8 will do the job. The jist of the myth is that these filters are the only ones that have a low enough resistance to allow sufficient airflow for the system to operate adequately.

Dust holding capacity defines the amount of dust an air filter can hold when it operates at a specified airflow rate to some maximum resistance value. Look for an arrow on the filter indicating airflow. As the filter loads up with the stuff it catches the resistance increases. To determine resistance filters use the merv rating system.

Going through the filter material the air encounters resistance. Air cleaners which have a thick media filter can trap small particles like pet dander and mold without impeding air flow like a thin pleated air filter would. In short the higher the merv rating is the more resistant the filter is. Resistance refers to the static pressure drop across the filter at a given face velocity.

To build some good comparative data we tested 20 different air filters of various types thicknesses and efficiencies. If you re really interested in keeping your air clean we d suggest you get an air cleaner purifier installed in your air ducts. Our test duct is 8 feet long two feet wide and two feet high. They also found that air flow in the high merv filters dropped by 7 and 11 in the two hvac systems compared to the low merv filters.

The smaller pores in more highly rated air filters create resistance to air flow and if the filter is used in an hvac system that is not designed to handle this resistance it can lower the system s efficiency decrease indoor air quality and put strain on the system s fan. If your unit is older and or very sensitive with airflow use a filter that ranks from merv 1 up to possibly merv 6. How much resistance depends on the type of filter material and the amount of area. Using a filter with a higher merv rating could mean that your hvac system runs longer than it would with a filter with a lower merv rating.

Higher dust holding ability meaning it can catch a lot without blocking airflow longer life most pleated 4 in and 5 in deep media filters will last between 6 months to a year between changes do this. The standard fiberglass filter doesn t resist the air flow much at least not when the filter is clean. It removes more contaminants from the air but it means that your furnace or air conditioner has to work harder to push the air through your home. Start by turning off the furnace.