Air Purifiers FAQ
Air purifiers are appliances that remove particles (dust, hair, pollen, bacteria, viruses, etc.) and harmful contaminants from the air that affect lungs, irritate airways, and worsen allergies. Air purifiers pass these particles through highly efficient air filters to improve air quality. These devices are often shaped like sophisticated portable fans and come in both domestic and industrial models.
What’s the solution? Air purifiers! They’re designed to clean the air that circulates in your home so that your indoor air stays clean, and your family can live a healthy life.
According to the EPA, indoor air contains more than five times more contaminants than outdoor air. Air inside a home often circulates unfiltered for days before being replaced. Unfortunately, air that is usually filled with contaminants like dust, pollen, or pet dander, which can cause severe respiratory problems and chronic fatigue. Below diagram shows different pollutants and their particle size in microns (one-one millionth of a meter).
Air purifiers are the best way to clean your air indoors. They also help maintain a healthy environment by removing pet dander, mold spores, ragweed and more. If you don’t think an air purifier is the right choice for your home; here are 10 reasons to reconsider: 1. Air purifiers ensure your family is breathing clean air.
2. Air purifiers remove unpleasant odors.
3. Air purifiers trap airborne allergens released by pets.
4. Air purifiers help neutralize smoke.
5. Air purifiers trap dust.
6. Air purifiers remove up to 99 percent of airborne bacteria.
7. Air purifiers combat seasonal allergens.
8. Air purifiers stop sickness and germs and viruses from spreading.
9. Air purifiers keep your lungs healthy.
10. Air purifiers fit everywhere.
While most air purifiers contain HEPA (High-Efficiency Particulate Air) filters, some air purifiers include other types of filters such as activated carbon filters or UV light filters. Some advanced air purifiers include a combination of two or three types of filters.
- HEPA (High-Efficiency Particulate Air): Air purifiers with HEPA filters can capture pollutants as little as 0.3 microns in size. These tiny particles cannot even be seen by human eyes. The smallest particles visible to us are at least 50 or 60 microns in size.
- Activated Carbon: Air purifiers with activated carbon filters effectively trap odors. They can’t capture viruses and bacteria like HEPA filters can.
- Electrostatic Precipitators: Air purifiers with electrostatic precipitators use high voltage electrical energy, charging the particles passing through the filters. The dead pathogens keep accumulating on the electrostatic plates. To maintain the efficiency of the filter, these electrostatic plates need to be changed regularly. Electrostatic precipitators also release ozone, a reactive gas that is potentially damaging to our lungs.
- Ultraviolet Light Air Purifiers: These air purifiers use UV rays to kill the germs floating in the air. Some UV light air cleaners release ozone as well, so check before buying this type of purifier.
- Ozone Generators: Air purifiers with ozone generators absorb odors. But the high levels of ozone released by these air purifiers make the room unsuitable for use for the next 24 hours. Exposure to even low levels of ozone can cause chest pain, coughing, and shortness of breath. Prolonged exposure damages lungs and aggravates respiratory problems.
Air Purification Systems are generally separated into 3 categories:
1. Mechanical air purifiers, which clean the air by trapping dirt in a filter made of some type of media.
2. Electrostatic air purifiers trap dirt by electronic magnetism.
3. The Third uses some other device to clean the air of specific items; for
instance, UV filters remove live organisms.
|Technology||Efficiency Range||Particle Size||Advantages||Disadvantages|
|Fiberglass Media||3 – 5%||0.3 – 1 micron||Inexpensive||Very low efficiency|
|Electrostatic Media (No electric charge)||15 – 30%||0.3 – 1 micron||Relatively inexpensive||Efficient only on larger particles|
|Electret Media (Electrically charged)||40 – 90%||0.3 – 1 micron||High efficiency on large-medium size particles||Low efficiency on smaller particles|
|Medium Efficiency Media||35 – 60%||0.3 – 1 micron||Low airflow resistance||Require replacement filters|
|High Efficiency Media||60 – 95%||0.3 – 1 micron||High efficiency on many smaller particles||High airflow resistance|
|HEPA Media||0.997||0.3 – 1 micron||High efficiency on many smaller particles||High airflow resistance|
|Ozone Generator (emission of the highly reactive molecule-O3)||inconclusive testing information||0.3 – 1 micron||Ideal for removing odor after fires||No particle collection May irritate asthma Considered dangerous by the EPA and OSHA|
|Ionizer (negatively charged ions)||inconclusive testing information||0.3 – 1 micron||Relatively low cost||No particle collection Largest particles may be re-circulated|
|Electrostatic Precipitator||Up to 97%||0.01 microns||High efficiency on many smaller particles||Filter must be maintained|
When air passes through an air purifier, contaminants, debris, and microscopic particles are removed to provide a high level of air quality. Some purifiers are designed to remove specific types of contaminants. You may want to use a filter made of paper, mesh, fiber, carbon, or other materials depending on your budget and the type of air quality issue that you are looking to address. Thus, to effectively do their job, air purifiers need to perform 2 actions:
1. Create airflow through the air purifier (measured in CFM). These devices need to gather all the unclean indoor air to have the ability to remove numerous pollutants.
2. Use effective filters to purify the air. The filters are the heart of every air purifier; they capture the pollutants in the indoor air. The created clean air is expelled out of the air purifier by the continuous airflow.
The basic air purifier works by creating an airflow through its filtration system (with several filters that gather air pollutants).
The key component of any air purifiers is the air filter. Air is generally filtered through meshes that remove harmful particles that can cause allergies or other health issues. There are 4 primary types of filters used in modern air purifiers:
1. Nylon Filters: These are the same filters that air conditioners use. Nylon filters are simply thin meshes that retain dust and other large particles. Nylon filters are also known as pre-filters. Since these filters are made out of foam or nylon, they can be washed and re-used. Thus not only the pre-filters act as good blockers for large particles, they have a good longevity too.
2. Active Carbon Filters: This filter is composed of pure, porous carbon that transforms offensive air particles into solids through a chemical process. Activated carbon is made up of several compounds that only allow the passage of particles smaller than 50 nm (Nanometers). This part of the filter traps tiny biological particles that cause health issues and odors.
3. Synthetic Bag Filters: Better known as the G4 filter, this variant looks like a plastic sheet but contains ultra-thin nylon yarns. It functions similar to the nylon filter, but the meshes are treated with chemicals to filter even finer particles of dust or bacteria.
4. HEPA Filters: High efficiency particulate air (HEPA) filters are quiet, compact, and extremely effective. According to the American Society of Mechanical Engineers, HEPA filters must be able to remove 99.97% of small particles (0.3 micrometers) from any air that passes through them.
5. HEGA Filters: HEGA stands for High Efficiency Gas Absorption, and this type of filter was developed about a decade ago by the British Army as a defense against chemical warfare. HEGA filters are composed of a carbon cloth and are considered to be many times more efficient than granulated activated carbon at adsorption of gaseous pollutants, chemicals, and odors.
HEPA is a type of pleated mechanical air filter. It is an acronym for "High Efficiency Particulate Air [filter]" (as officially defined by the U.S. Dept. of Energy). This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm). The diameter specification of 0.3 microns responds to the worst case; the Most Penetrating Particle Size (MPPS). Particles that are larger or smaller are trapped with even higher efficiency. Using the worst-case particle size results in the worst-case efficiency rating (i.e. 99.97% or better for all particle sizes).
All air cleaners require periodic cleaning and filter replacement to function properly.
The Minimum Efficiency Reporting Values, or MERVs, report a filter's ability to capture larger particles between 0.3 and 10 microns (µm). • This value is helpful in comparing the performance of different filters
• The rating is derived from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) [see www.ashrae.org ].
• The higher the MERV rating the better the filter is at trapping specific types of particles.
|MERV Rating||Average Particle Size Efficiency in Microns|
|1-4||3.0 - 10.0 less than 20%|
|6||3.0 - 10.0 49.9%|
|8||3.0 - 10.0 84.9%|
|10||1.0 - 3.0 50% - 64.9%, 3.0 - 10.0 85% or greater|
|12||1.0 - 3.0 80% - 89.9%, 3.0 - 10.0 90% or greater|
|14||0.3 - 1.0 75% - 84%, 1.0 - 3.0 90% or greater|
|16||0.3 - 1.0 75% or greater|
Ion generators act by charging the particles in a room so that they are attracted to walls, floors, tabletops, draperies, occupants, etc. Abrasion can result in these particles being resuspended into the air. In some cases, these devices contain a collector to attract the charged particles back to the unit. While ion generators may remove small particles (e.g., those in tobacco smoke) from the indoor air, they do not remove gases or odors, and may be relatively ineffective in removing large particles such as pollen and house dust allergens.
Ozone, a lung irritant, is produced indirectly by ion generators and some other electronic air cleaners and directly by ozone generators. While indirect ozone production is of concern, there is even greater concern with the direct, and purposeful introduction of a lung irritant into indoor air. The Food and Drug Administration has set a limit of 0.05 parts per million of ozone for medical devices. So, when considering to buy an ionizer or an ozone generating air purifier, make sure the level of ozone it generates is within the safety zone.
UVC light air purifiers kill biological organisms such as bacteria and viruses. UVC is a kind UV light with the wavelength of about 254 nanometers. When a living cell passes close enough to a UVC light the DNA of the cell is damaged. These cells have to be exposed to UVC light for extended periods. The length of time needs varies from cell to cell and the intensity of the UVC light that hits the cell. The closer the cell comes to the light bulb the better. UVC light is especially effective on viruses and bacteria. The average bacterium is killed in 10 seconds if it is within 6 inches of the UVC Bulb. For an air purifier this means the bacteria would probably have to go through the filter several times. Some bacteria are collected by the filters and exposed to the UVC light for an extended period of time.
When buying an air purifier, it’s crucial to check certain factors such as its HEPA filtration ratings. To reap the maximum benefits from your air purifier and avoid certain negative effects, consider the following factors:
Different air purifiers are designed to clean the air in rooms of specific sizes. Check the air purifier for its compatible room size. Air purifiers are most effective when they are compatible with your room size. To save on energy bills, buy a model meant to be effective in a slightly bigger room. That way, the air purifier continues to be effective even at a lower setting.
Most air purifiers with HEPA filters produce noise ranging from 35 to 70 decibels. The noise level depends on the operational settings. To avoid sleep disruptions due to noise, opt for air purifiers which are effective even set to a lower noise level.
Look for true HEPA filters, avoiding purifiers with “HEPA like” or “HEPA type” filters. True HEPA filters are the most efficient because they can capture minute pathogens. If you want to avoid odors and gases as well, try air purifiers with HEPA and activated carbon filters.
Asthma and Allergy Friendly Certification
Many household products on the market claim to control allergens, but sometimes these claims are exaggerated. To help consumers make an informed decision, the Asthma and Allergy Foundation of America in association with Allergy Standards Limited (ASL) has created a certification program. Before certifying products, they run the products through many tests to ensure the air purifiers remove most of the harmful particles. Once the home air purifiers clear all the tests covered under the program, they earn the “asthma & allergy friendly” mark. The certification assures you a quality product with superior air filtration abilities, perfect for allergy sufferers as well.
Clean-Air Delivery Rate (CADR)
The air purifier’s CADR specifies its overall cleaning speed for a particular size room. It shows the speed at which the purifier can filter dust, smoke, and pollen particles (three of the most common indoor air pollutants). Smoke particles are the smallest and can range between 0.1 to 0.3 microns. Dust particles vary between 0.5 to 3 microns, while pollen particles are around 5 to 11 microns. High CADR indicates the filters can purify the air quickly. CADR is measured in cubic feet per minute (CFM). For example, an air purifier with 400 CFM will purify the air in a 400 square feet room much faster than an air purifier with 300 CFM. On average, bedrooms are between 250 to 350 square feet in size. Air purifiers with CADR 300 to 400 should be perfect for average-sized rooms.
Air Change Per Hour (ACH) Rating
The ACH rating shows the number of times per hour the entire volume of air in your room gets filtered. A higher ACH rating indicates better efficiency. If you are prone to allergies or asthma, it’s best to opt for purifiers with at least a 4x or 5x ACH rating. That way, you ensure the indoor air is filtered at a faster rate. Frequent filtration reduces the chances of leaving behind pathogens in your indoor environment.
Some air purifiers generate ozone during the filtration process. Ozone gas can be damaging to your respiratory system. Before buying, check if the air purifier emits ozone gas.
When buying an air purifier, you should factor in the maintenance cost as well. The maintenance costs are dependent on how often you have to replace your filter. You should also factor your HEPA filter use in your energy bill. Some air purifiers, such as those with UV lights, include washable filters, but they need more watts to function. This may inflate your electricity bill. UV light air purifiers may not be as effective as HEPA air cleaners because many bacteria are UV-resistant. HEPA air cleaners are energy-efficient, but the filters should be changed once in three months for optimum benefits. Generally, replacing filters cost around $100 per year. If you buy an air purifier with a combination of filters, you may spend more on changing filters. For example, if your air purifier contains HEPA and activated carbon filters, you will have to change both filters every 3 to 4 months, and that may end up costing you more than $100 per year.
To choose the right size air purifier for your needs, consider the square footage of the room you want to purify. If you have allergies or asthma and are looking for an air purifier to help manage your symptoms, you should also consider an air purifier’s air change per hour (ACH) rate. ACH refers to the number of times an air purifier can filter the entire volume of air in the treatment space each hour. Effective air cleaners should have enough capacity to clean a room at least 2 – 4 times each hour. A 20’ by 20’ work or living space can efficiently and effectively be cleaned by a model with a 210–275 cfm rating. A rate of four air changes per hour also that the air purifier thoroughly cleans the air. Below is a rough size guide for air purifiers with an ACH of four:
• Small: These air purifiers are designed for personal space or rooms up to 299 square feet.
• Medium: Find an air purifier for rooms between 300 and 699 square feet.
• Large: Use these air purifiers in rooms between 700 and 1,900 square feet.
There are several things to consider when buying an air purifier to ensure that you get the best performance:
• Where will you use the purifier?
• Do you have specific needs such as removing pet dander or smoking residue?
• Compare the CADR ratings.
• Purchase a device with HEPA filter technology.
• Never buy a purifier with plastic filter housing.
• Get a purifier with the lowest noise rating possible.
• Consider the cost of replacement filters and maintenance.
ACH: Air Change per Hour rate
Air Movement Rate: Air movement rate, measured in cubic feet per minute (cfm).
CADR: Clean Air Delivery Rate
HEPA: High Efficiency Particulate Air [filter]
HEGA: High Efficiency Gas Absorption [filter]
MPPS: Most Penetrating Particle Size.
To improve your indoor air quality, follow some other steps such as regular cleaning, growing indoor plants, and maintaining proper ventilation. The following steps can further improve your indoor air quality:
- Vacuum clean the floor and carpets at least once a week to prevent allergen build-up.
- Grow indoor plants. They act as natural air filters, diluting the carbon dioxide levels in the room.
- Use dehumidifiers to avert mold and mildew growth.
- When the air purifier is not in use, open windows for fresh air. If possible, allow cross-ventilation by opening windows at opposite ends of the room.
- Turn on the exhaust fans in the kitchen to dissipate smoke after cooking. The exhaust fan also dries up ambient air in the bathroom and laundry room, otherwise, humidity can lead to bacteria and allergen growth.