Everything You Need to Know About HVAC Air Filters

Dirty air filter being removed from a homes unit.

In 2023, Carbon Valley residents used their heating and cooling systems a lot. In fact, according to the National Weather Service, we had 330 days with temperature lows below 60° and 96 days with temperature highs over 80° F.

That is a lot of time your air filter is being used. Many people overlook the importance of air filtration when considering indoor air quality (IAQ). A proper heating, ventilation, and air conditioning (HVAC) system should have a high-quality filter as part of the system.

The air filter’s job in the HVAC system is to keep the units clean and help avoid breakdowns caused by dirt and debris. Without a filter, the HVAC system may have problems draining water away as dirt gets trapped in the drain.

There may be indoor coil issues that arise as unfiltered air blows across the wet coils and dirt and debris get stuck in the condensate and stick to the coil. The same problem applies to ductwork as the dirty air travels past the unit and into the ductwork.

The dirty air catches in the ductwork and can cause improper airflow. In each case, water can be trapped, and this, in turn, might allow mold and other allergens to grow and flourish.

Even the most basic filter is better than no filter, not only for your HVAC system but for your family in residential settings and employees in commercial settings.

How it Works

The U.S. Environmental Protection Agency (EPA) describes indoor air pollution as one of the top five environmental health risks. For people with allergies, scientific studies have shown that air filtration reduces these airborne allergens and may provide some relief.

The World Health Organization has provided recommended standards covering three ranges of particle sizes, specifying guidelines for acceptable particulate matter concentrations.

The human eye can only see particles as small as 25 to 60 microns—or the diameter of a human hair—but the particles that are most dangerous to human health are significantly smaller and invisible to the human eye (PM 2.5 and PM 1).

The Minimum Efficiency Reporting Value (MERV) rating is determined by measuring particle counts upstream and downstream of the air-cleaning device being tested; the more particles removed by the filter, the higher the MERV rating is.

There are 12 particle sizes being tested. Dust spot efficiency is used to show how effective it is at filtering smaller particles of atmospheric dust from the air. Arrestance is the ability to filter and remove larger particles of dust. A High-Efficiency Particulate Air (HEPA) filter can accomplish over 99.97 percent arrestance of these finer air particles.

CAUTION: As the MERV rating goes up, the performance of your HVAC system can be affected. Adding a 15 MERV filter to a system that was designed for 8 MERV increases resistance.

The blower in the furnace or air handler is rated for a certain amount of pressure drop, and increasing resistance increases the pressure drop, which may cause reduced airflow throughout the system, leading to reduced filtration, reduced comfort, the air conditioning coil to freeze up, and even the furnace heat exchanger to crack.

Be sure your system is able to accept a higher MERV-rated filter before installing one. When considering replacing an HVAC system or just a filtration system, make sure a professional considers and verifies that the system operation is correct.

MERV Ratings

  • 1-4 MERV

Setting for Use: Standard Residential and  Standard Light Commercial

Effectiveness: Use for up to 80 percent of larger particles and under 20 percent of smaller particles filtered

Examples of particles filtered effectively are sanding dust, spray paint dust, and carpet fibers.

Common filter types in this range are flat-panel fiberglass and washable/reusable

  • 5-7 MERV

Setting For Use: Good Residential, Better Light Commercial, Industrial Workplaces

Effectiveness: Up to 90 percent of larger particles and up to 30 percent of smaller particles are filtered.

Examples of particles filtered effectively are pollen, pet dander, and hair spray.

Common filter types in this range: 1-2 inch cotton pleated and flat-panel fiberglass

  • 8-12 MERV

Setting for Use: Superior Residential, Good Light Commercial, Commercial, Good Industrial Workplaces

Effectiveness: Up to 95 percent of larger particles and up to 75 percent of smaller particles filtered

 Examples of particles filtered effectively are welding fumes, auto emissions, milled flour, lead dust, pollen, household dust, lint, mold spores, Legionella, and dust mites.

 Common filter types in this range: 1-2 inch cotton pleated, media panel filter, and extended surface deep pleated

  • 13-16 MERV

Setting for Use: Hospitals and Health Care Facilities, Superior Residential, Superior Commercial, Superior Industrial Workplaces

Effectiveness: Greater than 95 percent of larger particles and greater than 98 percent of smaller particles filtered.

Examples of particles filtered effectively are tobacco smoke, general smoke, all bacteria, Droplet Nuclei (sneeze), cooking oil, smog, and virus carriers.

Common filter types in this range: Media panel filter, extended surface deep pleated


When it comes to comfort and air filtration, a proper analysis by an advisor needs to be made. A lot of factors come into play, such as what type of building it is, whether anyone has any allergies, whether anyone has a weak immune system, and can the MERV can be increased without compromising the airflow.

Other factors that play a role in comfort are the cost of installation and the cost of replacement filters.

Did you know?

Approximately 50 percent of all illnesses are caused or exacerbated by poor indoor air quality, according to The American College of Allergy, Asthma & Immunology. A study cited by Kimberly-Clark Corporation found that for every 10 workers, poor indoor air quality caused an additional 6 sick days per year.

The U.S. Department of Energy (DOE) states poor indoor air quality can cost businesses up to $168 billion annually. Medical care and absenteeism contribute significantly to those costs.

Employers can increase workforce performance by roughly 10 percent by implementing indoor air quality solutions, according to the DOE.

By controlling contaminants such as dust mites, asthma cases can be reduced by 55 to 60 percent, according to the American Journal of Respiratory and Critical Care Medicine.

DIY Indoor Air Quality Tips

Using an air filter is just one step toward improving the overall quality of indoor treated air. Here are some other things you can do to help IAQ:

  • Do not smoke in the building.
  • Use a vacuum cleaner with a HEPA filter to reduce dust, dander, and other allergens.
  • Keep humidity in your home below 50 percent year-round.
  • If you have a pet, groom the pet outside the home to reduce the amount of pet dander in the air.
  • If you have tiled floors or walls, make sure they are kept clean to reduce the potential for mold growth.
  • Check and/or change your filter regularly, at least once a month, and once every two weeks if you have pets.
  • Use Zero and Low VOC paint indoors.
  • Spray paint in the garage or outdoors.
  • Plants are natural air purifiers, but beware, if you suffer from allergies, they may hurt more than help.
  • Limit the use of candles—or use beeswax candles, which let off less smoke.
  • Professional carpet cleaning can treat carpets for pets and allergens.
  • Make sure to turn on the exhaust when you are cooking; this can greatly reduce oil and smoke.


Thermostat: Some models have maintenance features that will remind you to check/replace the filter.

Ionizers use high voltage to ionize (electrically charge) air molecules. Negative ions, or anions, are particles with one or more extra electrons, conferring a net negative charge to the particle. Effective against other particles normally reserved for a higher MERV count. Examples are viruses, bacteria, mold spores, and smoke.

Ultraviolet (UV) Light is designed to help eliminate mold, bacteria, viruses, and other allergens that can be circulated in the air.

Helpful Carbon Valley Tips

1. Change and/or check once a month, reset alert on thermostat if applicable

2. Install a filter with a MERV rating of 10 or higher, if possible, which takes out 85 percent or better 3-10 microns. The Minimum Efficiency Reporting Value (MERV) rating is used to rank the efficiency of air filters. MERV 10 takes out 50 to 64 percent of particles 1-3 microns, MERV 14 takes out 90 percent of 1-3 microns particles, and 75 to 85 percent .3 to 1 microns.  MERV 16 takes out 95 percent or better .3-1 microns

3. UV lights need the light replaced once a year generally. Reduce disease transmission by preventing or eliminating mold and bacteria

4. Air ionizer: make sure it is operational if equipped with an indicator light; some models are self-cleaning. Kills mold, bacteria, and viruses. Controls odors from smoking, pets, and cooking. Reduces static electricity.

Carbon Valley Heating & Air Service Advantage

  • We fill out any necessary paperwork to guarantee your product becomes registered with the manufacturer.
  • Our service team is highly skilled and experienced; we pride ourselves on making sure we only recommend the replacement of parts and equipment as a last resort.
  • We offer free consultations on new equipment and second opinions. We want to make sure that every option is given to you for your system and your building in a way that makes sense for your comfort needs.
  • We put our customers’ interests above our own; since 1999, Carbon Valley Heating and Air has built a reputation as a company that provides great products and outstanding service at a competitive price while focusing on high-quality work.

Call Us Today

Schedule a free consultation with Carbon Valley Heating & Air to upgrade the air quality in your Longmont, CO, home. Call us at 720-383-7911 or request service online.

Need HVAC Service?

Contact the experts at Carbon Valley Heating & Air.

Call us at 303-833-4466!

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