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Quick Introduction to Air Filters & Cleaners

Airflow Systems: Chapter 2

Air Filter

In this module, we will explore the purpose of air filters. We will also learn about the most important filters and air contaminants. Skip to quiz!


Air is full of small contaminants like dust, pollen, and more. These particles can be harmful to our lungs and health. The purpose of an air filter is to prevent these particles from traveling through a building!

Air filters remove contaminants so that only clean air enters a building. Air filters are placed on vents, furnaces, air conditioners and other parts of an HVAC system.

Air Contaminants

Recall that air is a mixture of nitrogen, oxygen, and some other gasses. Anything that is not normally found in air is a contaminant. Contaminants can be solid and liquid and gaseous.

Contaminants can be anything from dust and pollen to more serious ones like bacteria and viruses. Contaminants can also come from pet hair and human hair. Air filters want to remove all types of these contaminants.

Air filters remove contaminants because some can be very harmful. Dust and smoke can cause bronchitis, asthma and even lung disease. Mold and pollen can cause serious allergy reactions.

Different contaminants come from different sources. Mold spores occur when there is high humidity. Pollen comes from plants. Many harmful contaminants come from factories and cars.

Air filters trap contaminants when they pass through them. Air filters act like a strainer for pasta. The water is small enough to get through but the noodles are not. The air filter works the same way except it’s holes are much smaller.

Types of Filters

There are different types of air filters that can trap different size particles. Air filters that are more closely knit can trap smaller particles than ones with bigger holes.

Here are the main types of filters.

Let’s take a look at what each is used for!

Panel Fiberglass filters are disposable and inexpensive. They keep out most large particles but not dust and smaller particles. People with respiratory problems may require better filters.

Pleated media filters are slightly more expensive than panel fiberglass filters.They are better at filtering dust and smaller particles like pet hair. These filters are the most commonly used filter.

Reusable filters are also called washable filters.They can save you money because they can be reused rather than buying new ones. However, if you put it back in while still wet, they can can grow mold.

Electrostatic filters use electrostatic charge to trap smaller particles. Think about when you rub a balloon on your head and the electrostatics causes it to stick to your hair. The same thing happens with the electrostatic filter and dust and smoke particles.

UV-Light filters became more popular during the Covid-19 Pandemic. These filters use ultraviolet light to kill bacteria, viruses and microorganisms in the air. However, they are not very good at removing dust and other matter.

HEPA stands for High Efficiency Particulate Air. HEPA filters are capable of removing very small particles. They can remove 99.97% of irritants from the air.

ULPA stands for Ultra Low Particulate Air. These are the highest quality filters available. They can remove 99.999% of irritants from the air!

Filter Life Span

Different filters have different lifespans. Even different disposable filters last for different amounts of time. Disposable filters should be checked once a month and changed when they get dirty.

Pleated filters last longer than panel fiberglass filters. This is because they can trap more contaminants. This is why pleated filters are more common than fiberglass.

When contaminants get trapped by a filter, it makes it harder for air to get through the dirty filter. This means the HVAC system has to work harder to pump enough air into a room through the filter.

HVAC system working harder results in high energy bills and reduced life-span. Dirty filters do not allow cool or hot air through it easily. So, it affects the comfort of occupants in the room by restricting the airflow.

Filters are very important to keeping the air of your home clean.Installing the correct filter prevents health problems and minimizes your energy bill.


Filter Properties

In this module we will learn about the different traits of various air filters. We will discuss how to pick the most effective filter for different scenarios. Skip to quiz!

Filter Efficiency

Recall that efficiency is a measure of how well a system operates. Filter efficiency is defined as the extent to which filters remove air contaminants. Air filters with higher efficiency are more effective at cleaning the air than lower efficiency filters.

A common method to measure filter efficiency is called arrestance. Arrestance uses particles of a very specific size to test the filter Let’s take a look at how it works!

In this method, we measure the weight of dust cap

tured by the filter. Then we compare it to the weight of the dust that was released. A filter with an efficiency of 50 percent arrestance captures half of the material passing through.

Filter efficiency helps regulate which filters are good enough. ASHRAE is the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.They help to both regulate and advance the science of HVAC. Let’s take a closer look at what they do.

ASHRAE has developed a standard for the world to know what filters are best.The standard is called ‘Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency.’ It also helps us understand MERV values

MERV stands for Minimum Efficiency Reporting Values. MERV ratings range from 1 to 20. The higher the MERV rating, the more efficient the filter is.

Panel fiberglass filters typically have a MERV rating of 4. Pleated media filter are rated between 5 and 8. HEPA filters have a range between 17-20 and ULPA have a rating of 20.

The Right Filter

Recall that an HVAC filter is used to trap contaminants. This can only be done if you choose the correct filter for a certain system.

If someone in your home suffers from breathing problems, a low quality filter is not good enough. A high quality filter causes unnecessary stress on the HVAC equipment.

Picking the right filter is very important in high risk environments like hospitals. If the filter quality is too low it may result in harm or death to patients.

Contaminant Size

Contaminants fall in four different size ranges. There are different suitable filters for each size range of contaminant.

Contaminants such as pollen, hair, lint, sand and carpet fibers fall in this range. They are controlled by filters with a MERV rating between 1 and 4. Panel fiberglass filters are the best filter for trapping large contaminants like these.

Contaminants such as dust pent dander, perfume spray and mold spores fall in this range. They are controlled by filters with a MERV rating between 5 and 8. Pleated media filters are the best filter for contaminants of this size.

Contaminants such as humidifier dust, lead dust, vehicle emissions, and welding fumes fall in this range. MERV 9 -12 filters are the best filter for contaminants of this size.

Contaminants such Bacteria, tobacco smoke, droplets from sneezing fall in this range. They are controlled by filters with a MERV rating between 13 and 16. HEPA filters are the best filter for contaminants of this size.

Choosing the best filter is important to maintain clean and healthy air. The best filter can be determine by looking at the MERV rating. This information avoids air contamination with our unnecessary air blockage.


Air Cleaners

In this module we will learn what air cleaners are and where they are used. Skip to quiz!

What is an Air Cleaner?

An air cleaner is a device that removes pollutants from a room. They can stand alone or be attached to HVAC systems. Different air cleaners have different methods of removing contaminants. Let’s explore some!

Recall that an air filter is built into an HVAC system and prevents contaminants from flowing through. Air cleaners, however, eliminate or remove contaminants that are already there.

Electronic Air Cleaners use an electric charge to remove impurities from the air. They can remove both solid and liquid contaminants.

Fans pull air into the air cleaner. The air passes through a metal filter. This filter catches the large particles. Small particles have a slight electric charge. This charge attracts them to the filter. The clean air then leaves the filter.

Electronic air cleaners have many applications. Let’s take a look at some of their uses.

Steam production plants burn wood and coal to generate power. This produces harmful smoke. Electronic air cleaners are used to clean the smoke before it leaves the plant. This prevents air pollution.

Electronic air cleaners are also used in chemistry labs. Many experiments create dangerous mist. The cleaners prevent this mist from harming the scientists.

They can be used in hospitals to remove fungi and bacteria from the air. Some of these electronic air filters even have UV lights implemented in them.

UV lights in electronic air cleaners can remove microorganisms. The electric charge alone is not enough to attract and kill these particles.

Other Air Cleaners

There are many different air cleaners that all have different uses. They all use different technology to achieve cleaner air. Let’s take a look at some of them!

Ultraviolet air cleaners use ultraviolet light to remove potentially harmful viruses, bacteria, and mold. Ultraviolet technology was first used in hospitals to disinfect patient beds.

HEPA air cleaners use HEPA air filters to decontaminate rooms. Just like their air filter counterpart, this cleaners are very effective at removing small particles.

Activated carbon air cleaners can remove smoke, odors, fumes, and gasses.These are good for people who are sensitive to smoke.

Ionic air purifiers are extremely quiet and operate without a motor. They emit negative ions into the air, which bond with positively charged air contaminants like dust. This makes these particles so heavy that they eventually fall out of the air.

Central air cleaners connect to the HVAC system. This allows them to clean your entire home.

These cleaners work by removing old air and bringing in new clean air. The new air is free of contaminants and the contaminants leave with the old air.

Air cleaners are very important to keep our air free from contaminants. Different air cleaners can be used to eliminate different particulates.Thanks to air cleaners, we can be sure the air we breathe is safe.


Question #1: Where are air filters placed?

  1. Underground

  2. In HVAC systems

  3. Doorways and windows

Scroll down for the answer...

Answer: In HVAC systems

Air filters need to trap particles as the air flows through. That is why they are placed in HVAC systems.

Question #2: Which of these is not a harmful air contaminant?

  1. Pollen

  2. Dust

  3. Nitrogen

  4. Smoke

Scroll down for the answer...

Answer: Nitrogen

Nitrogen is part of the normal mixture of breathable air. It is not a contaminant.

Question #3: What is the most commonly used filter?

  1. Electrostatic Filter

  2. Reusable Filter

  3. Panel Fiberglass Filter

Scroll down for the answer...

Answer: Panel Fiberglass Filter

Panel Fiberglass filers are the most commonly used because they are inexpensive. They also eliminate most common contaminants.

Question #4: What air filter would you use to remove viral bacteria?

  1. Electrostatic Filter

  2. Reusable Filter

  3. UV Light Filter

  4. Panel Fiberglass Filter

Scroll down for the answer...

Answer: UV Light Filter

UV Light filters and remove bacteria, viruses, and microorganisms. The other three filters other air contaminants.

Question #5: Pleated filters are better than fiberglass because they are reusable.

  1. True

  2. False

Scroll down for the answer...

Answer: False

Pleated filters are not reusable. They are better filters because they trap more contaminants.

Question #6: Who develops standards for filters and efficiency?


  2. HVAC

  3. MERV

  4. HEPA

Scroll down for the answer...

Answer: ASHRAE

ASHRAE is the society of engineers that sets standards for HVAC systems. MERV is the scale on which filter efficiency is measured.

Question #7: It is always more beneficial to use a high quality air filter rather than a low quality one.

  1. True

  2. False

Scroll down for the answer...

Answer: False

High quality air filters can put unnecessary stress on a system.

Question #8: Which filter is best for large contaminants >10 micrometers.

  1. Panel Fiberglass

  2. Pleated

  3. MERV 9 - 12

  4. HEPA

Scroll down for the answer...

Answer: Panel Fiberglass

Panel fiberglass filters can trap large contaminants such as pollen, hair, lint and sand.

Question #9: Air cleaner is just another word for air filter.

  1. True

  2. False

Scroll down for the answer...

Answer: False

Air filters are part of the HVAC system. Air cleaners are generally their own device.

Question #10: Electronic Air cleaners utilize ____ to trap particles

  1. Charges

  2. Energy

  3. Weight

  4. Magnets

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Answer: Charges

Electronic air cleaners attract particles with small positive and negative charges.

Question #11: Electronic air filters alone cannot kill bacteria. Which of the following is used with them to do so?

  1. Gamma rays

  2. Chemical mist

  3. UV Lights

  4. Magnets

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Answer: UV Lights

UV lights are able to kill microorganisms like bacteria and fungi.

Question #12: Which air cleaner is the best at removing gases?

  1. Activated Carbon

  2. HEPA

  3. Ultraviolet

  4. Electronic

Scroll down for the answer...

Answer: Activated Carbon

Activated carbon air filters are good for removing gases. They are not as effective in removing other particles.

Question #13: Which of the following air cleaners can clean an entire home or building?

  1. Air-to-Air Exchanger

  2. Central Air Cleaner

  3. Ionic Air Cleaner

Scroll down for the answer...


Answer: Central Air Cleaner

Central Air Cleaners can connect to the HVAC system to clean the whole home.


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