What Are the Different HVAC Filter Ratings?

The heating and cooling world is filled with different types of ratings and their corresponding acronyms. We’ve got SEER for air conditioners, AFUE for furnaces, HSPF for heat pump heating, and more! When it comes to HVAC filter ratings, it’s all about MERV – which stands for minimum efficiency reporting value. Read on to find out what MERV means and how to find the right air filter rating for use with your heating and air conditioner system.

What Do HVAC Filter Ratings Measure?

The ratings you see on HVAC equipment such as furnaces and air conditioners reflect the unit’s energy efficiency in various ways. HVAC filter ratings are often said to measure efficiency as well, but in reality, they measure the filter’s effectiveness when it comes to removing debris and contaminants from the air that circulates through it. MERV ratings tell consumers how well (or how poorly) the filter performs and how effective the filter is at removing airborne particles of a certain size.

How Are HVAC Filter Ratings Assigned?

MERV was created in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and has since been used to show HVAC filter ratings. Air filters are tested by taking particle counts from the air volume using standard dust patterns over a set number of cycles. The MERV rating assigned to a filter reflects its arrestance, or ability to filter out synthetic dust; dust spot efficiency, which is the ability to remove atmospheric dust; and particle size ranges.

The MERV Rating Scale

The MERV rating scale runs from one to 20. One represents the lowest efficiency performance, while 20 represents the highest efficiency performance. The higher the MERV rating, the more effective the filter. As MERV increases, so does a filter’s ability to capture small particles and more of them. Basic MERV charts show average particle sizes and their efficiencies for ranges of ratings, while expanded charts will show more details such as each rating’s efficiency at capturing various-sized particles.

In general, MERV measures for HVAC filter ratings are grouped as follows:

  • MERV 1 to 4: Basic filtration of particles between 3 and 10 microns in size, which are generally some pollen, dust mites, carpet fibers and cockroach debris. These filters are used in home HVAC systems.
  • MERV 5 to 8: Improved air filtration for particles between 3 and 10 microns in size, which also includes mold spores, dust, pet dander and lint. These filters are used in homes as well as commercial or industrial applications.
  • MERV 9 to 12: Some filtration of particles between 1 and 3 microns and up, including vehicle fumes, lead dust and large bacteria particles. These air filters are used in some residential HVAC systems as well as home air cleaner systems, and can be found in some commercial buildings.
  • MERV 13 to 16: Offers filtration of particles between 0.3 and 1 microns in size and up, such as bacteria, tobacco smoke, sneeze particles, legionella and mineral dusts. These filters may be used within a home air cleaner system and are found in hospital environments that require high filtration.
  • MERV 17 to 20: Offers the best filtration of particles 0.3 to 1 micron and up, with the ability to trap viruses, carbon dust and all bacteria. These air filters are used in clean room environments.

Types of Filters and How They Rank

Air filters are an important part of any home’s heating, ventilation and air conditioning system, as they help to remove contaminants from the air, improving indoor air quality. There are many different types of air filters available on the market, and each has its own benefits and drawbacks. Common filter types include:

Fiberglass Filters

These disposable filters are made from layers of fiberglass material with a metal grate to reinforce the fiberglass batting. They are designed to trap particles in the air before they can enter your HVAC system. As they have a low MERV rating, typically between MERV 1 to 4, they will not remove all contaminants from the air. They provide minimal contaminant protection for your HVAC system and do little to benefit air quality indoors. As a result, they may not be the best choice for homes with poor indoor air quality.

Electrostatic Filters

Reusable electrostatic air filters are made up of a series of flat metal plates that are charged with static electricity. As air passes through the filter, the charged particles are attracted to the plates and trapped on the surface to capture contaminants including dust, bacteria and pollen. 

The filter is reusable and must be cleaned about every month. Some reusable electrostatic air filters can last for years with proper care. A typical electrostatic filter has HVAC filter ratings from MERV 1 to 4, so they aren’t highly effective for contaminant removal or indoor air quality improvements. However, there are some models available with HVAC filter ratings up to about MERV 8.

Pleated Media Filters

Pleated filters are a type of air filter that is made from pliable cotton, polyester or paper. The material is accordion-folded, which increases its surface area and improves its filtration efficiency. These filters typically have a MERV rating of between 5 and 13, but there are also high-efficiency MERV 14 to 16 options. One downside to pleated media filters is that they are disposable; once they become full of debris, you must replace them. 

Reusable Pleated Filters

Pleated reusable filters are a type of air filter that is designed to be used multiple times. They are made of woven polypropylene material and typically have a pleated surface area, which in turn improves their efficiency at capturing contaminants. Their HVAC filter ratings are commonly between MERV 5 to 13.

Additionally, pleated reusable filters can be combined with an electrostatic charge, which helps to further improve their performance. While they tend to be more expensive than other types of reusable air filters, their improved performance is typically worth the extra cost. These filters do need to be washed regularly, about every 30 to 90 days.

HEPA Filters

HEPA filters are made of a matted material that consists of glass or synthetic fibers. The fibers are arranged in a way that creates tiny pores that allow air to pass through, but they are small enough to trap dangerous particles, such as pollen, dust mites and pet dander. HEPA filters typically have HVAC filter ratings of MERV 17 to 20, which means that they are able to remove 99.97% of all particles that are 0.3 microns in size or larger from the air. 

Choosing the Right HVAC Filter Ratings for Your HVAC System

Typically, a pleated media filter with a MERV 8 to 13 rating is a good choice for home HVAC systems when it comes to HVAC air filter ratings. With these filters, you gain better filtration for improved air quality, and they last longer than lower-rated filters. Your furnace or air handler owner’s manual should state the maximum HVAC filter ratings for use with your equipment.

Should I Use Filters with the Highest HVAC Filter Ratings?

When selecting a furnace filter for use with your home’s HVAC system, the MERV rating must be considered. While you want to find a filter that offers effective contaminant removal that is capable of controlling common contaminants in your home, you must be aware of the limitations of your HVAC system’s equipment. It’s easy to conclude that everyone should use MERV 20 furnace filters at home because they are the best, but actually doing so can lead to serious problems.

The higher MERV rating a filter has, the smaller the pores are across the filter’s surface. Smaller pores give the filter the ability to capture smaller particles, but in turn, the filter’s makeup also creates airflow resistance. This means it is harder for air to circulate through the filter and into the HVAC unit.

Hindering airflow in the pursuit of superior air filtration is not wise. When heating and cooling equipment doesn’t receive adequate airflow, units can overheat, components can sustain damage and the systems can experience difficulties keeping your home at a comfortable temperature. Thus, the HVAC filters with higher MERV filter ratings aren’t necessarily the best choice for your home or HVAC system.

Air Filter Help from Grove Heating & Cooling

If you have questions about HVAC filter ratings or selecting the right HVAC filter for your heating and cooling system, we’re here to help. Contact us today to discover the best filter for use in your Maryland home to improve your indoor air quality.

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