One of the most overlooked components in a modern HVAC system is the air filter. To a certain extent, this is understandable, it’s an inexpensive part and it’s easy to change. And yet, for some reason many people forget about changing their air filter. There is no one-size-fits-all advice on air filter replacement frequency because every home is different. But, as a general rule of thumb, it’s advisable to change the air filter every 90 days. In this article, we will take a closer look at what happens when a regular air filter change is not carried out.

What is an Air Filter and Why Do I Need One?

Before we look at the consequences of missing HVAC air filter changes, let’s take a look at what they are and why you need them in your system. Most modern air filters are made from spun fiberglass, which is the same material as your attic insulation. Some models are made from pleated paper and they typically have a cardboard rim to improve rigidity and stability. These air filters are inserted in a housing within the return air duct and this is usually a drop down vent in the hallway or other location.

The air filters are physical barriers that allow air to pass through while the airborne particulates are trapped on the surface and left behind. Most residential filters can block a wide variety of contaminants, such as: dirt, dust, lint, mold, bacteria, pet hair and more. Every air filter has a Minimum Efficiency Reporting Value (MERV) rating that ranges from 1-20 and the higher the number the smaller the particles that it can capture. The air filter acts as a barrier to prevent airborne contaminants from entering the system where they can cause damage to components.

Understanding MERV Ratings

According to data from the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) air filtration does improve indoor air quality (IAQ). The higher MERV rated filters remove more contaminants because the filter media is denser. When an air filter has a MERV rating of 16 or lower it’s considered to be a high grade filter for commercial, industrial and general hospital use. At a MERV rating of 17 and higher up to a MERV rating of 20, they are designed for clean rooms, surgical operating rooms and other locations that require the utmost cleanliness.

Many people learn this information and come to the natural conclusion that they should install a MERV 20 rated HVAC air filter in their homes. After all, the smaller pores and denser media would make huge improvements to the IAQ. But, there is a drawback because the air must be forced through the filter to keep the air flowing. This requires considerable effort as the MERV rating rises because they are denser and it’s harder to force the air through the media. A residential HVAC unit doesn’t have sufficient power to move the air through these higher efficiency air filters. In fact, they won’t be able to accommodate them anyway because the air filter housing will be the wrong size. Even if your HVAC system could run a high MERV rated air filter, this would make the energy bills skyrocket. The extra energy required to push the air through the filter would be significant. The performance and energy efficiency would be degraded if a higher rated MERV air filter was in-place. The best residential MERV rating is 8-11 for standard air filters which would be sufficient for most homes. But, if you want better IAQ you can go up to a MERV rating of 13 with a High Efficiency Particulate Air (HEPA) filter which can remove more harmful contaminants.

What is the Ideal Frequency of Air Filter Changes?

As we mentioned earlier, three months or 90 days is the benchmark that most HVAC companies recommend as the minimum for air filter changes. But, there are a number of factors to consider for your home, they are: the location (dusty or dry), the age of your HVAC system, pets in the home, the presence of allergy sufferers and more.

The single largest consideration is probably pets, many people have furry friends residing in their homes. But, if you take a look at the surface of an air filter you may notice that it’s clogged with dead skin cells and pet hair. So, if you have pets, it’s a good idea to change the air filters every two months or 60 days to keep the filter clear.

If there are allergy sufferers or people with pre-existing respiratory problems, change the air filter every 20-45 days to improve the IAQ.

If you have a vacant or vacation home, you can change the air filters every 9-12 months when the HVAC system isn’t running. If you use the home more, you will need more frequent air filter changes.

What Happens if I Don’t Use an Air Filter or Forget to Change it?

The primary purpose of the air filter is to protect the sensitive components in the HVAC system. A modern heating and cooling system represents a significant investment and you need it to run efficiently for as long as possible to recoup that money. When you run the HVAC system with no air filter in place, those airborne contaminants are forced into those components. This typically leads to loss of performance, a lack of energy efficiency and frequent repair bills. In extreme cases, it may even lower the useful lifespan of your system leading to an earlier than expected replacement.

Although the improvements to the IAQ are a secondary function, they are still important. This is especially true for allergy sufferers and people that struggle to breathe. The presence of dust, pollen, mold spores and other contaminants can trigger allergic reactions and make breathing even harder.

In Conclusion

Changing the air filter is simple, the full instructions are detailed in the owner’s manual for your system. If you want to schedule a tune-up for your HVAC system or an upgrade, contact your local heating and cooling specialist today.