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HVAC systems have plenty of technical moving parts: evaporators and condensers, heat exchangers, blower fans, dampers, and so on. But it may surprise you to learn that one of the most important parts of the HVAC system is a small, inexpensive part that's easy to overlook: the air filter. Knowing how an air filter works as part of your larger heating and cooling apparatus, knowing how to maintain air filtration, and knowing how to go about choosing air filters from among the options are key to understanding your HVAC system and how best to keep it running.

What Does the Air Filter Do?

An air filter is a mesh of fibers in a rigid frame, which forms a sort of a strainer. The air filter is placed in the path of circulating air to catch small particulates such as dust, pollen and pet dander, as well as larger items like bits of insulation traveling in the air supply. This has two effects: it prevents these particulates from entering the HVAC system and clogging it up or being sucked into the furnace flame, and it improves indoor air quality by removing these allergens from the air.

Why Is Air Filter Replacement Important?

If you have a central HVAC system, odds are that all the air in your house flows through the air filter.

As the air filter catches more and more airborne particulates, it becomes more and more clogged by them. This means that air has a harder time passing through the mesh, which has certain effects on system performance. For one thing, the blower fans have to work harder to keep pushing air through a clogged mesh, which increases energy use and puts strain on the motor. With additional strain comes increased chance of failure. In fact, neglected air filters are the number one cause of HVAC system failure.

A clogged air filter also restricts airflow, which means that furnaces are in more danger of overheating, and heated or cooled air has a much harder time making it to all areas of your house. Because thermostat sensors aren't usually placed near the HVAC units themselves, the thermostat will continually report a less comfortable temperature than the system should be producing, so the demand on the system will continually increase. This can gobble up a lot of energy and overtax the furnace or A/C. It also makes it difficult to get to and maintain a comfortable indoor temperature.

Air filters should be replaced every month or two, though depending on environmental factors (a smoker or pets in the household, high pollen counts, etc.), you may need to replace them more frequently. Knowing your air filter options can help when it comes to choosing air filters that are best for your home's particular system and needs.

Air Filter Options

If you haven't spent a lot of time considering your HVAC system's air filter up to this point, the different air filter options available can be daunting. Here's a brief guide to what you're looking at when you go to the air filtration aisle in the hardware store:

  • Pleated and polyester air filters are standard go-tos when you're choosing air filters. They can catch a good percentage of the airborne pollutants in the air supply, are relatively cheap, and require no maintenance other than periodic replacement.
  • Fiberglass air filters are typically only used in situations where air cleaning is handled elsewhere, such as with a standalone air cleaner or an electrostatic air filter in the ductwork. They're extremely cheap, but these filters do nothing to filter particulates out of the air. They're only used to prevent larger items, such as bits of paper or loose insulation, from being pulled into the HVAC system.
  • Washable air filters were developed to appeal to thrifty and environmentally-conscious homeowners' sensibilities. While nice in theory, they're often more trouble than they're worth. They tend to have a low ability to filter particulates out of the air, and they can hold moisture after being washed, creating the perfect environment within your air supply for mold and bacteria to grow.
  • High-efficiency air filters, such as HEPA filters, are powerful air-cleaning filters that are able to remove a majority of the particulate pollutants from indoor air. Used in hospital cleanroom settings and airplanes, they may be overkill for many residential setups, though households with very young children, elderly residents or immunocompromised individuals may benefit from them. One thing to be aware of is that they provide so much filtration that most residential HVAC fan motors aren't designed to push air through them, so install these as a standalone air filter or work with an HVAC contractor to upgrade the blower fan to prevent motor burnout.

MERV Ratings

Knowing the minimum efficiency reporting value (MERV) can also help when it comes to choosing air filters for your system. The MERV rating is a measure of how effective the filter is at cleaning the air and how well it filters smaller particles. Low MERV ratings in the 1-4 range are only effective at filtering out large particles like pet dander, insect debris and pollen. Filters on the high end of the range (13-16) can catch bacteria and particles as small as face powder or smoke. HEPA filters go beyond the traditional MERV range, but can be thought of as MERV 17-20. They can filter viruses out of the air, which is why they're used in cleanroom settings.

The higher the MERV rating, the more resistance the filter provides to air passing through. Always check the HVAC system's documentation for the recommended filter range before choosing air filters with high MERV ratings.

Other Ways to Boost Indoor Air Quality

You can extend your air filter's life and improve indoor air quality by supplementing air cleaning with another system. Here are some options:

  • A standalone air cleaner – These units often offer HEPA filtration, meaning that your air will be cleaner overall, and a much lower level of particulate pollution will pass through the system's air filter. These can be installed centrally to take care of the air in your entire home, or installed in certain rooms, such as basement workshops.
  • Electrostatic air cleaners – If you've ever built up a static charge on a balloon and used that to pick up small objects, you know the principle behind these air cleaners. Installed inside the duct system, electrostatic air cleaners use a static charge to pull particulates out of the air. When they're dirty, they can be washed with soap and warm water and easily dried and replaced.
  • Humidifiers and dehumidifiers – In high-humidity areas and seasons, a dehumidifier can bring the humidity down to a point where mold, fungus and bacteria won't be so eager to grow. When the humidity is low, raising it can prevent dust buildup and prevent the degradation of paper and wood. Balanced humidity can raise your indoor air quality in a variety of ways.
  • Ultraviolet (UV) lights – Installed inside the HVAC system, these lights can sterilize – though not filter – air. This means that circulating mold and fungal spores and bacteria will be unable to land and start colonies, which would otherwise introduce more organic pollutants into your air supply.

If you're curious about choosing air filters from the wide array of air filter options, or you want to learn more about boosting indoor air quality in your Baltimore area home, contact Griffith Energy Services today!

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