Your air filter plays a key role in how your HVAC system operates on a day-to-day basis. Nevertheless, it's also one of the most overlooked components of any typical HVAC system. If you haven't forgotten how often to change your air filter, then chances are you might not know which air filter you should use for your HVAC system. The following offers an in-depth guide on selecting the best air filter to use for your heating and cooling equipment.
What's the Word on MERV?
The MERV rating system is the most widely used method for determining which air filter performs best. You'll find MERV ratings listed prominently on most air filter packaging, although some brands may use their own rating system. The idea behind MERV was to help consumers compare among multiple air filters to find the one that best suited their needs.
Here's a quick breakdown of the MERV rating system, along with the common types of air filters used:
MERV 1-4: Standard fiberglass air filters are often rated within this tier. These filters provide minimal levels of air filtration at a very affordable cost. The majority of washable air filters are also rated at this tier.
MERV 5-8: At this tier, fiberglass air filters give way to air filters using pleated paper filter elements. Pleated air filters rated at this tier offer superior filtration performance over standard fiberglass air filters.
MERV 9-12: Air filters rated at this tier offer significantly better filtration performance than ordinary pleated air filters. These filters are capable of capturing particulates as small as 1 micrometer in size.
MERV 13-16: Air filters rated at this tier are capable of capturing particulates as small as 0.3 micrometers, usually at the cost of increased airflow restriction. These high-efficiency filters are typically used in commercial and hospital settings.
MERV 17-20: High-efficiency particulate air (HEPA) filters are usually the only air filters capable of achieving such lofty ratings. These filters using extraordinarily fine mesh to trap tobacco smoke, viruses, bacteria, and a wide variety of other extremely fine particulates.
To take some of the guesswork out of choosing a good air filter, your HVAC system manufacturer may recommend you use an air filter with a specific MERV rating. Stepping up to a better quality air filter with a slightly higher MERV rating may prove beneficial for achieving better indoor air quality, especially if you have allergy sufferers in your home and need the additional filtration performance to keep common allergens and other asthma-triggering pollutants at bay.
IAQ vs. Airflow
There's an interesting level of give-and-take when it comes to HVAC air filters. As the filtration mesh shrinks in order to capture smaller particles, gains in filtration performance often come at the expense of airflow. It's possible for an air filter to become so dense that it significantly slows down your HVAC system's normal airflow rate. This makes striking a balance between indoor air quality and airflow especially important when choosing your next air filter.
Air filters rated at MERV 13-16 are particularly restrictive in terms of HVAC airflow, especially for ordinary residential HVAC systems that aren't designed to overcome the additional restriction. HEPA filters are even more restrictive thanks to their extremely fine mesh. If you want to use a HEPA filter for your current HVAC system, it'll need extensive modifications before it can be safely used without severely impacting its performance.
For this reason, higher MERV ratings don't always mean better performance. According to the U.S. Environmental Protection Agency, air filters rated between MERV 7 and 13 are likely to offer the same effectiveness in removing harmful particulates as true HEPA filters. It's crucial to choose an air filter that offers the filtration performance you want without starving your HVAC system of its normal airflow.