Home / Equipment

What Is MERV Rating? Air Filter Rating Chart

5/24/23

As air moves through a building’s HVAC system, air filters trap and collect large and small particles such as dust, allergens and microorganisms. Numerous studies document their role in improving indoor air quality. A filter's MERV number indicates how it's rated to remove these particles. But what is MERV rating, exactly?

An air filter’s minimum efficiency reporting value (MERV) rating measures how effectively the filter stops dust and other contaminants from passing through the filter and into the air stream. MERV ratings are from 1-16, and filters with higher MERV ratings trap small particles more effectively than filters with lower MERV ratings.

In general, filters with a rating of MERV 16 or below are considered to be HVAC-system-grade filters for residential, commercial and general hospital use. Though ratings don't go higher than MERV 16, high-efficiency particulate air (HEPA) filters trap the smallest particles at a higher rate than even MERV 16 and are typically used in surgical operating rooms, clean rooms and other contexts that require absolute cleanliness.

MERV Filter Ratings and Efficiency

When selecting the right filter for your application, higher is not always better. Using an air filter with a MERV rating higher than what your furnace or air conditioner manufacturer recommends can actually impair its performance.

The smaller pores in more highly rated air filters create resistance to air flow, and if the filter is used in an HVAC system that is not designed to handle this resistance, it can lower the system's efficiency, decrease indoor air quality and put strain on the system's fan.

MERV Filter Ratings and Air Quality

Researchers in India compiled a range of studies that considered the effect of air filtration on indoor air quality and the resulting positive health outcomes.

Those studies found that filtering recirculated air improved microvascular function in healthy elderly people, improved another type of vascular function in healthy adults and resulted in better lung function in indigenous communities, among other benefits.

Use the MERV rating chart below to understand which filters are best for which applications.

MERV Rating Chart

Rating Application Contaminants Particle Size

 

MERV 2

MERV 3

MERV 4

Pre-filter in commercial building

Residential furnaces

Window air-conditioning units

Pollen

Dust mites

Sanding dust

Textile/carpet fibers

Filters down to 10.0 micron particle size

Pre-filters or final filters

Commercial buildings

Better residential Buildings

Industrial workplaces

Paint booth inlets

Pollen

Dust mites

Sanding dust

Textile/carpet fibers

Mold/spores

Dust lint

Cement dust

Filters down to 3.0–10.0 micron particle size

Pre-filters or final filters

Hospital laboratories

Better commercial buildings

Superior residential buildings

Pollen

Dust mites

Sanding dust

Textile/carpet fibers

Mold/spores

Dust lint

Cement dust

Legionella

Lead dust

Humidifier dust

Coal dust

Nebulizer dust

Filters down to 1.0–3.0 micron particle size

Final filters

General surgery

Superior commercial buildings

Hospital inpatient Care

Smoking lounges

Pollen

Dust mites

Sanding dust

Textile/carpet fibers

Mold/spores

Dust lint

Cement dust

Legionella

Lead dust

Humidifier dust

Coal dust

Nebulizer dust

Bacteria

Tobacco smoke

Auto fumes

Sneeze nuclei

Insecticide dust

Copier toner

Pet dander

Face powder

Filters down to 0.3–1.0 micron particle size

Final filter

Clean rooms

Radioactive raterials

Pharmaceutical manufacturing facilities

Carcinogenic materials

Orthopedic surgery room

Pollen

Dust mites

Sanding dust

Textile/carpet fibers

Mold/spores

Dust lint

Cement dust

Legionella

Lead dust

Humidifier dust

Coal dust

Nebulizer dust

Bacteria

Tobacco smoke

Auto fumes

Sneeze nuclei

Insecticide dust

Copier toner

Pet dander

Face powder

Virus carriers

Carbon dust

Sea salt

Combustion smoke

Radon progeny

Odor

Microscopic allergens

Filters down to less than 0.30 micron particle size

Pre-Filters vs. Final Filters

Air filters can be used as final filters or pre-filters. When used as final filters, they are the primary filters for an HVAC system. Final filters may be used alone in a single-filter system, or they may be used in combination with one or more pre-filters. When used in a multi-filter system, the pre-filters trap the dirt and large particles before the air reaches the final filters downstream, which then remove the smaller particles. This multi-filter system extends the life of the more expensive final filters, leading to overall cost savings.

Frequently Asked Questions

Q: What MERV filter is recommended for preventing the transmission of airborne illnesses?

A: To filter out infectious airborne particles, ASHRAE recommends that organizations use MERV-13 or the highest achievable filtration level, though MERV-14 (or better) is preferred. 

Q: Can HVAC operations strategies help prevent the spread of COVID-19?

A: Commercial HVAC operations may help decrease people's exposure to airborne pathogens that spread COVID-19 and other illnesses. Building technology group ASHRAE notes that while the virus causing COVID-19 in smaller than 0.3 microns, it is often embedded in other airborne particles that are large enough to be captured by air filters. ASHRAE has compiled recommendations for filtration, humidity set points, automation and more.

RECOMMENDED KNOWHOW FOR YOU

Sustainability

Driving Sustainability with MRO Consumables Purchasing

Purchasing decisions have many kinds of environmental impacts. How can you decide what really matters?

Safety Management

Abrasive Safety: Understanding the Hazards

Read about the hazards of working with abrasives and get some guidance on how to prevent injuries.

PPE in the Workplace

Safety Quiz: How Much Do You Really Know About PPE?

How well do you know your safety gear? Test your knowledge with our short quiz to ensure you’re up to date with key safety practices.

Our Latest KnowHow

Driving Sustainability with MRO Consumables Purchasing

Purchasing decisions have many kinds of environmental impacts. How can you decide what really matters?

10 Factors to Consider When Choosing a Fastener

Choosing the wrong fastener can cause structural issues, downtime and high maintenance costs. Learn key factors to select the best fastener.

Abrasive Safety: Understanding the Hazards

Read about the hazards of working with abrasives and get some guidance on how to prevent injuries.

Find the Right Cooling Products

Air Conditioners

Air Conditioners

Evaporative & Misting Coolers

Evaporative & Misting Coolers

Cooling Fans

Cooling Fans

Ventilation

Ventilation

Air Purifiers, Dehumidifiers

Air Purifiers, Dehumidifiers & Treatment

Mini-Split Systems

Mini-Split Systems

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.