HVAC Filters

A nominal size air filter refers to the rounded, labeled dimensions of the filter, not its actual measurements. Nominal sizes are slightly undercut to ensure the filter fits properly into standard housings. For example, a filter listed as 24" x 24" x 1" Nominal will typically measure approximately 23-1/2" x 23-1/2" x 3/4" Exact.

An exact size air filter, on the other hand, is manufactured to the precise dimensions requested. For example, a filter specified as 18" x 24" x 1" Exact will be delivered at 18" x 24" x ¾", with no undercutting.

It’s also important to note that people often confuse the actual size of the filter with the size of the opening or track it fits into. Always measure the physical filter itself, not the housing, to ensure the correct size is ordered.

The efficiency range depends on the specific type of air filter you’re looking for, but HVAC filters are commonly available from MERV 6 up to MERV 16. Lower MERV ratings are suitable for general dust control and basic air quality needs, while higher MERV filters capture much finer particulates and are used in more demanding environments.

Selecting the correct efficiency is important to ensure a balance between airflow performance and particulate removal. Choosing a filter that is too restrictive for your system can reduce airflow, while choosing one that is too low-efficiency may not provide adequate protection.

If you need assistance determining the right MERV rating for your application, our Application Engineers are happy to help you select the best option for your process.

The primary purpose of an air filter in an HVAC system is to remove dust, debris, and airborne contaminants from the air before it enters the heating or cooling equipment. This protects internal components from dirt buildup, reduces wear on the system, helps maintain efficient airflow, and minimizes maintenance on the coils. In addition to equipment protection, the air filter also improves indoor air quality by capturing particulates that would otherwise circulate throughout the building.

MERV 13–15 air filters can capture a significant portion of airborne particles in the size range associated with many virus-containing respiratory droplets and aerosols, but they do not guarantee complete virus removal. These filters are effective at reducing airborne particulate levels and improving overall air quality, and they can help lower the concentration of virus-carrying particles in the air but no HVAC filter can fully eliminate viruses on its own.

Several factors affect performance, including the HVAC system’s airflow capacity, filter fit and sealing, run time, humidity levels, and the size of the airborne droplets. In residential systems, upgrading to a higher MERV filter must also be balanced with ensuring the system can handle the additional resistance without reducing airflow or straining the equipment.

For the best overall protection, MERV 13–15 filtration is most effective when combined with proper ventilation, humidity control, make-up air, surface cleaning practices, and—when needed—supplemental air cleaning (such as HEPA portable units).

If you’re unsure whether your HVAC system can support a MERV 13 or 15 filter, our Application Engineers can review your system specifications and recommend the safest and most effective filtration option.