Timberline Blog

How HVAC Filtration Needs and Filter Change Frequency Are Determined

October 27, 2021 by Timberline

Having the right HVAC system is crucial to creating a comfortable and healthy environment for your business or home. There are many aspects to “right” in this context, of course, but one of the most important is the degree of air filtration your system provides.

HVAC engineer

It would be understandable for building owners and homeowners to see it as an easy decision: “Let’s get the highest filtration level available!” However, there are several factors that make that type of snap decision unwise. Instead, it’s important to learn a little about air quality and air filtration, and then use that knowledge to determine your actual filtration requirements.

Understanding Air Filter MERV Ratings

Whether you’re installing a new HVAC system or upgrading an existing one, it’s important to have the right type of filtration. And a good place to start is understanding MERV ratings. MERV is short for Minimum Efficiency Reporting Value. It’s a measure of an air filter’s ability to capture larger particles—those between 0.3 and 10 microns (µm).

This rating is based on a test method created by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). In short, the higher the MERV rating of a filter is, the better the filter is at trapping particulate matter. Ratings range from 1 (minimal filtering) to 20 (maximum filtration, which is rarely used outside of hospitals and “cleanroom” environments).

Important Environmental Considerations for Choosing Your HVAC Air Filtration Level

How do you determine the right air filtration level for your building or home? There are many environmental factors to take into account, including:

  • How a space is used. If a commercial space is used for some type of industrial purpose that generates particulate matter, for example, a higher MERV level (above 8) may be needed to effectively and fully remove the particles from the air. In a home, on the other hand, there typically isn’t a significant amount of particulate matter in the air, so a lower MERV level (below 8) will probably suffice.
  • The health of those who use a space. If air quality affects an occupant’s health—a homeowner who has a breathing condition that’s worsened by particles in the air, for instance—it may be helpful to use air filters with a higher MERV level.
  • The presence of pets and people who have allergies. Another health issue that can affect the selection of a MERV rating is allergies. In particular, many people have pet allergies, and a higher MERV level can result in air that’s freer of dander and other allergens, and therefore is less likely to trigger allergies.
  • Persistent odors. If the use of a space generates objectionable odors, filters with a higher MERV rating may help control them. There are also charcoal-based filters that can help neutralize odors.

Understanding these factors helps our HVAC experts at Timberline Mechanical begin to develop a MERV level recommendation for you. However, that recommendation is also affected by mechanical considerations.

Key Mechanical Considerations for Choosing Your HVAC Air Filtration Level

The conditions in a building or home and the needs of the occupants are very important. But your choice of air filtration MERV level is also dependent on your HVAC system. Specifically, the higher the MERV level of an air filter is, the harder it is for air to move through it. And the backlog of air waiting to pass through a high-MERV filter creates resistance, or a condition referred to in the HVAC business as “pressure drop.”

Not only does pressure drop mean that less air comes out of vents, but it can also lead to components of a heating or air conditioning system overheating or freezing up respectively. So, to use high-MERV filters, you have to have an HVAC system that will support it. In some cases, what’s called “fan balancing” (increasing your system’s fan speed) can compensate for a higher MERV rating.

And, not surprisingly, these mechanical factors lead to one other important consideration: cost. Higher-MERV air filters are more expensive, as you might expect. But the bigger cost is modifying your existing system or replacing it so that you have the right equipment for the level of filtration you desire.

Beware of the HEPA Hype

The terms “HEPA filter” and “HEPA filtration” get thrown around a lot, which has led to them being considered by some to be the “gold standard” in air filters. But they really just have a higher MERV rating.

HEPA stands for “high-efficiency particulate air.” Filters that meet this standard have a MERV rating of 16 or higher. HEPA filters are made to remove at least 99.97% of dust, pollen, mold and bacteria particles. You might see them referred to as “hospital-grade” air filters.

Their effectiveness in removing particulate matter from the air is impressive. But the question that should be asked is, “Is that level of air filtration necessary for us?” Unless you operate a hospital or cleanroom, the answer is almost certainly, “No.”

Determining Your Air Filter Replacement Frequency

Regardless of what MERV level you choose, it’s critical that you change your air filters regularly. How often is “regularly”? As with selecting a MERV rating, there are several factors involved in determining the appropriate filter-change frequency for your system.

How many hours does your system run on a given day? Do you have pets in your home? Does your business create airborne dust and debris? What is the quality of the unfiltered air inside and outside your building or home? The answers to these questions are important to consider, but ultimately you need to inspect your filters at least monthly until you have a good sense of how long it takes them to start accumulating a noticeable amount of material.

At that point, changes in your answers to the questions above may be indicators that you need to reconsider how frequently you change filters. For instance, you previously had no pets but just adopted two large dogs. You may find yourself needing to change your filters more frequently.

“Clear the Air” With Timberline Mechanical

If you need a new HVAC system installed or an existing system serviced or upgraded, our HVAC technicians can provide expert service. And if you have questions about air filtration, MERV levels and the needs of your business or home, we’re happy to answer them. Contact Timberline Mechanical today!

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