What Is an Air Filter in HVAC?

Air filters are designed to remove contaminants, such as dust, allergens, pollen, microorganisms and other particulates from the air as it passes through the HVAC system of a building or vehicle, according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). Air handler units (AHU’s), mobile air filters, and air handler accessory units use many air filtering concepts. Electronic air filters use a different method involving the use of an electric charge to attract and capture particles.

There are many types of air filters available, ranging from fiberglass air filters to High-Efficiency Particulate Air (HEPA) filters and Ultra-Low Particulate Air (ULPA) filters. HEPA and ULPA filters can also be used in whole house air purification systems, which are designed into the HVAC system to filter the air throughout a home or building.

An air filter improves indoor air quality and ensures optimal performance of the system. The efficiency of an air filter is rated using the MERV scale, and it is important to regularly check and replace air filters to maintain good indoor air quality and prevent clogged air flow.

In some cases, you may choose to use two air filters, such as a high-efficiency filter in conjunction with a fiberglass filter in order to improve both effectiveness and long-term affordability. Alternatively, you may choose to use an inline filter, which is installed in the ductwork of the HVAC system, in addition to a filter within the air handler unit.

What Is a Fiberglass Air Filter?

Fiberglass filters are made from a mat of glass fibers that are woven together to create a porous structure. As air passes through the filter, the fibers trap contaminants, removing them from the air. Fiberglass filters are relatively inexpensive and are widely available on the market.

Fiberglass filters are generally less effective at removing fine particulates, such as smoke and allergens, compared to more advanced filters, such as High-Efficiency Particulate Air (HEPA) filters. However, they are still able to capture larger particles, such as dust and pollen, making them a good option for basic air filtration needs.

Fiberglass filters are often interchanged or (in commercial stacked with paper or cloth pleated air filters) which are made from layers of fiberglass wool media. In some cases, it may be beneficial to use two air filters in an HVAC system in order to provide high effectiveness. Pleated air filters are more effective at capturing smaller particles than fiberglass filters because of the finer air passage design, making them a better option for improving indoor air quality and removing fine particulates, such as smoke and allergens.

The market for air filters is expected to continue to grow, driven by increasing concerns about indoor air quality and the spread of viruses, although ASHRAE does not recommend a specific filter for preventing COVID-19 transmission. The market size for air filters is expected to reach over $16 billion by 2027, with fiberglass and pleated filters making up a significant portion of the market.

What Is a Pleated Air Filter?

A pleated air filter is a type of air filter that is made from multiple folded sheets of material, typically paper or synthetic fibers, bound into a frame. The multiple folded material equates to more area of filter than the frame itself occupies. These filters are designed to remove dust, dirt, and other contaminants from the air as it passes through the heating, ventilation, and air conditioning (HVAC) system. Pleated air filters are typically more efficient and have a higher dust-holding capacity than non-pleated air filters, such as fiberglass filters.

Pleated air filters are available in a range of efficiency ratings, including MERV 8, MERV 11, and MERV 13. Pleated air filters are also available in a range of sizes, including 1 inch, 2 inch, 4 inch, and 6 inch thickness, to fit different types of HVAC systems. The thicker pleated filter was designed to use a finer or lower MERV rated material while not increasing resistance or static differential. These filters can be used in a variety of applications, including residential, commercial, and industrial settings. Some pleated air filters, such as pleated HEPA filters, are designed to remove extremely fine particles from the air and are commonly used in hospitals and other sensitive environments.

While most pleated air filters are disposable and should be replaced when they become dirty or clogged, some are washable and can be reused multiple times. These washable pleated air filters typically have a frame made of metal, such as stainless steel, or a synthetic material, such as plastic. The filter media, with synthetic fibers, can be removed from the frame and washed with water or a mild detergent.

Pleated air filters are available in a variety of materials, including fiberglass, carbon, and paper. The specific material used in a pleated air filter will depend on the specific needs of the application and the type of contaminants that the filter is designed to remove. Some pleated air filters, such as those made from carbon, are specifically designed to remove odors and other gasses from the air.

Pleated air filters are commonly used in a variety of HVAC systems, including furnaces, air conditioners, and heat pumps. These filters can be installed in the air handler unit of the HVAC system, or they may be installed in a separate housing or cabinet. Some pleated air filters are available as panel filters, which are designed to fit into a standard air filter frame, or as cartridge filters, which are designed to fit into a specific type of housing.

Pleated air filters are often used in applications where high capacity filtration is required, such as in homes with allergies or other respiratory issues. These filters are available in a range of styles, including flat pleated, mini pleat, and ultra-pleat, to suit different types of HVAC systems and airflow requirements. Some pleated air filter materials are also available in roll form, which can be cut to size and used in a variety of applications.

What Is a HEPA Air Filter?

HEPA filters are designed to capture particles as small as 0.3 microns, making them particularly effective at removing fine particulates, such as smoke and allergens.

HEPA filters are used in a variety of settings, including homes, offices, and industrial environments. There are many brands that manufacture HEPA filters, including Xiaomi, Honeywell, Levoit, Bulex, Camfil, and others. These filters are available in a range of sizes and styles, including portable air filters that can be placed on a tabletop or in a small room, and larger, industrial-grade filters that are designed for use in larger spaces or HVAC systems.

HEPA filters can also be found in portable air purifiers, which are ideal for use in small spaces or on the go. Many portable air purifiers feature a combination of HEPA filtration and activated carbon filters to effectively remove a wide range of contaminants from the air.

Some popular brands of HEPA air purifiers include the Honeywell HPA300 True HEPA Air Purifier and the Levoit Air Purifier with True HEPA Filter. These purifiers are available for purchase on Amazon and other online retailers.

In addition to their use in air purifiers and HVAC systems, HEPA filters are also commonly found in car air filtration systems and furnace filters. The efficiency of a HEPA filter is often measured using the minimum efficiency reporting value (MERV) scale, which rates the filter’s ability to capture smaller particles.

What Is an ULPA Air Filter?

Ultra-Low Particulate Air (ULPA) filters are more effective at capturing fine particulates than other types of air filters, such as fiberglass filters and High-Efficiency Particulate Air (HEPA) filters, with the ability to capture particles as small as 0.12 microns, making them particularly effective at removing fine particulates, such as smoke and allergens. ULPA filters are commonly used in cleanrooms, computer chip manufacturing and other environments where ultra-pure air is required, such as hospitals, medical operating rooms, and other healthcare settings. They are also used in industrial air filtration systems and other settings where high levels of filtration effectiveness is required.

In addition to their use in HVAC systems, ULPA filters can also be found in air conditioners and furnace filters. It is important to regularly check and replace ULPA filters more often than standard MERV 13 filters to ensure that the HVAC system is operating at peak efficiency and to maintain good indoor air quality.

One of the key differences between ULPA filters and other types of air filters is the type of filter media used. ULPA filters are typically made from a fine mesh of polytetrafluoroethylene (PTFE) or other synthetic materials, which have a high degree of air permeability and a low pressure drop. This allows ULPA filters to capture smaller particles while still allowing for good airflow through the filter.

What Is Air Filter MERV Rating?

Air filters are rated from 1 to over 20 Minimum Efficiency Reporting Values (MERV), to describe a filter’s ability to capture larger particles between 0.3 and 10 microns (µm). A low MERV rating number of 1 may be used in a medical operating room, computer chip manufacturing or any high sterile application. According to the ASHRAE, the best rating for residential HVAC systems is MERV 13. However, changing to a lower MERV rating number will require a significant increase in the physical filter dimensions to prevent out of design air flow restriction. Before you upgrade your filter, make sure your specific system can accommodate that rating; MERV rating value affects air flow and static pressures greatly. ASHRAE does not recommend a specific MERV filter rating for preventing COVID-19 transmission, the organization suggests that upgrading systems in non-healthcare facilities to MERV-13 or the highest achievable level can be a worthwhile step in emergency response plans. 

Which Direction Should the Air Filter Face?

The direction of the air filter in an HVAC system determines the flow of air through the filter. The filter should be installed in the direction indicated by the arrows on the filter frame, with the arrow pointing in the direction of the airflow. This will ensure that the filter is able to effectively remove contaminants from the air as it passes through the HVAC system.

How Often Should an Air Filter Be Replaced?

It is important to regularly replace the air filter in your HVAC system in order to maintain its effectiveness. The frequency of filter replacement will depend on the specific HVAC system and the type of filter being used and the activities taking place in the filtered space. If you have a whole house air filter, it is especially important to keep the filter clean and replace it when necessary in order to maintain good indoor air quality throughout your home. Depending on the specific needs of your home, you may need to replace the air filter every one to three months.  Some filters are designed to be replaced on a monthly or quarterly basis, while others may last for several months or even up to a year. It is important to regularly check and replace air filters to ensure that the HVAC system is operating at peak efficiency and to maintain good indoor air quality.

A dirty air filter can impede the flow of air through the HVAC system, resulting in reduced efficiency and potentially causing damage to the system. It can also contribute to poor indoor air quality, as it may not be able to effectively remove contaminants from the air. As such, it is important to regularly perform HVAC maintenance, including replacing the air filter, in order to ensure that the system is operating effectively. On the other hand, a clean air filter can help to improve the performance of the HVAC system by allowing for optimal air flow and reducing the strain on the system’s components.

Some air filters are washable, meaning that they can be cleaned and reused multiple times. Other filters, such as fiberglass filters and pleated filters, are disposable and should be replaced when they become dirty or clogged. It is important to follow the manufacturer’s recommendations for the care and maintenance of your air filter in order to ensure that it is operating effectively.

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