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Air Filtration Basics: Understand Everything, From MERV to HEPA

In any indoor environment, the quality of the air you breathe will have a direct effect on your comfort and your health. Air filtration is your best method of defense against poor indoor air quality and the physical effects it can cause. Here is a brief introduction to air filtration and how it works, and how effective filtration can improve the quality and comfort of your indoor environment while also contributing to better respiratory function and improved overall health.

The Trouble With Indoor Air

We live in a society in which most of our labor and leisure is centered on indoor activities. Between work, school and home, plus all of the areas where we seek recreation, it is estimated that we spend more than 90 percent of our time indoors. Because of this, indoor air quality has a significant effect on the physical well-being of you and your family. The more you can improve the quality of your indoor air, the better you'll feel.

Some studies suggest that indoor air can be twice to five times as polluted as outdoor air. Indoor air commonly contains multiple types of contaminants that can trigger or aggravate asthma or allergy attacks. They can affect your respiratory health. They can cause and spread disease, or simply make you feel uncomfortable and ill.

Inorganic contaminants are usually particulates, which are extremely small fragments of solid material. Particulates can include:

  • Dust
  • Mold
  • Pollen
  • Fibers
  • Metal or wood fragments
  • Powders
  • Liquid droplets

Biological particulates include the many types of microorganisms that can cause disease and discomfort. They include viruses, germs, bacteria, dust mites, animal dander, mold spores and even fur, hair, and the waste and body parts of insects and other vermin.

Gaseous pollutants includes fumes, odors, exhaust gases, smoke, ozone, and radon. These indoor air contaminants can be produced by solvents, paints, household chemicals, cleaning supplies, pesticides, and even material intended to make your indoor environment better, such as deodorizers.

Even the most simple activities of daily living can produce airborne contaminants. Cooking, cleaning, even bathing can create conditions in which contaminants are created and indoor air quality suffers. We are often our own source of particulates: a major component of dust is the dead skin cells we are constantly shedding.

Air Filtration Fundamentals

To combat these diverse forms of indoor air pollution, you need a reliable and effective source of indoor air filtration. The most common source of air filtration is the air filter in your furnace, air conditioner or heat pump.

Your HVAC system is the first line of defense against indoor air pollutants. As your heating or cooling system functions, it produces a constant circulation of air between the inside of your home and the HVAC unit itself. Heated or cooled air is distributed through supply ductwork to your indoor areas, while return ductwork brings expended air back to be conditioned and redistributed. As air moves through the system, it is forced through the unit's air filter. The material of the filter captures the particulates in the air and holds them in place.

MERV Ratings and the Effectiveness of Air Filtration

The effectiveness of the air filters in your HVAC system, and by extension the quality of the air filtration the system provides, will be influenced by the quality of the filter.

Air filter quality is expressed by the filter's MERV rating. MERV stands for Minimum Efficiency Reporting Value. MERV numbers for standard air filters range from 1 to 16, and indicate how effective the filter is at trapping and holding airborne particulates of 0.3 to 10 microns in size. MERV ratings are based on factors such as the material used for the filter medium, such as cloth or fiberglass; the thickness of the filter; and the physical characteristics of the filter's collecting surface, such as pleated or flat. Higher MERV numbers indicate better levels of air filtration.

MERV ratings generally fall into one of four categories:

  1. MERV 1-4: These are inexpensive and readily available filters, but they are not very effective at removing most types of airborne contaminants. They are best at capturing bigger particulates of 10 microns or larger.
  2. MERV 5-8: Considered medium quality, these filters are very common. They are effective at removing contaminants of 3 microns and larger. They may be made of material such as pleated cloth, which creates additional surfaces for capturing and holding particulates.
  3. MERV 9-12: These high-quality filters are considered good options for most residential applications. They remove particulates of 1 micron or larger.
  4. MERV 13-16: These are the highest quality standard filters you can get for your HVAC system. They are very effective at removing particulates of 0.3 microns and larger. They will fit in most HVAC systems without the need for special frames or mountings.

When using high-MERV filters, remember that they can be very thick and dense, which can interfere with the airflow in your HVAC system. Impeded airflow can damage your HVAC equipment, so make sure your furnace or air conditioner can handle the thicker high-MERV filters before installing one. Your local trusted HVAC contractor can test your system's airflow and make any needed adjustments.

HEPA Filters: Extra Power for Your Air Filtration Needs

In some cases, you may want air filtration levels that exceed that offered by even the best standard filter. If so, HEPA (High-Efficiency Particulate Air) filters may be your best choice. HEPA filters provide air filtration at MERV levels of 17 to 20. They are extremely effective, removing 99.97 percent of the particulates found in indoor air. Activated charcoal or carbon inserts can also remove fumes, vapors and odors.

HEPA air filtration systems are sealed, self-contained units that are installed as an addition to your existing heating or cooling system. The airflow from your HVAC unit is routed through the HEPA unit. Inside, the extremely effective filters remove particulates before the air continues on its normal path through the HVAC system.

HEPA units capture airborne particles and other contaminants in three different ways:

  1. Interception: Particles are attracted to the surface of the filter when they come close enough to it.
  2. Impaction: As particulates move along with the airflow, they make physical contact with the filter and remain in place.
  3. Diffusion: Small particulates collide with other particulates or air molecules and are deflected toward the filter, where they are trapped and held in place.

The most common uses for HEPA filters are in settings where air quality is vitally important, such as medical facilities, computer clean rooms and factories that manufacture sensitive electronics. There are situations in which they would be appropriate in residential settings, such as when a resident has a respiratory condition that requires very clean indoor air.

Like other types of high-efficiency, high-MERV filters, HEPA systems can cause problems with the airflow in your HVAC equipment. Check your heating and cooling system for compatibility before installing a HEPA air filtration unit.

The Importance of Regular Filter Changes

As particulates and other material accumulate in the filters in your HVAC system, the effectiveness of the filter decreases and air filtration suffers. When an air filter is dirty or clogged, your furnace or air conditioner can't produce adequate airflow for proper system operation. Further, dirty filters are much less effective at removing contaminants from the limited amount of air that does manage to flow through them. Regular filter changes are vital to keeping your HVAC system working properly and to maintaining high levels of air filtration.

In general, HVAC air filters should be checked at least once a month and replaced if they are dirty. An effective method of determining if a filter is too dirty to use is to hold the filter itself up to a light source, such as a ceiling light or lamp. If you can't see light shining through the filter, it should be changed.

Filters should be changed every three months as part of regular system maintenance.

Regular filter changes will provide noticeable benefits such as:

  • Improved indoor air quality: Dirty filters can't capture and remove airborne contaminants effectively. Worse, the particulates they've already trapped can sometimes be dislodged and sent back into your home's indoor air. The cleaner you keep your filter, the cleaner your indoor air will be.
  • Better HVAC system performance and efficiency: If an air filter is dirty and clogged, it causes your furnace or air conditioner to work harder to produce heating or cooling. It will take longer for your HVAC system to heat or cool your home. This additional stress on the system increases energy use, which will drive your monthly utility bills higher than they should be.
  • Fewer malfunctions and breakdowns: Dirty filters are a primary cause of HVAC system problems. Blocked airflow produces stress on your HVAC system's components, such as the fans and air handlers, which increases wear and tear while making it more likely the system will malfunction or break down completely.

Customers in Chicago, northwestern Indiana, and southwestern Michigan can rely on Comfort24-7 for professional HVAC sales, installation, maintenance and repair. Contact us today for more information on air filtration and how it can keep your indoor environment more comfortable, or for help finding an air filtration system with the proper filters to use for your situation.

 

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