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Choosing a Portable Air Purifier

When your allergies are acting up, one of the best ways to feel better fast is to get away from whatever is causing the reaction.  Sometimes simply opening a window can ventilate a room with clean air and provide relief. Other times, weather makes this option impossible or allergens may also be present in the new air.  In such a case, an air cleaning system may be useful.

Air cleaners remove allergens from indoor air.  They can be installed in the ductwork of a home’s central heating, ventilating, and air-conditioning (HVAC) system to clean the air in the whole house or a portable room system can be used to clean the air in a single room only.   Installing a whole-home system may not be in your current budget, but depending on the type of allergy you are suffering from, a portable system may be sufficient for your needs and your wallet.

Types of Air Cleaners

There are a variety of air pollutants that can cause allergic reactions.    Air pollutants fall into two categories:  particulate matter and gaseous pollutants.  Particulate matter includes dust, smoke, pollen, animal dander, tobacco smoke, dust mite allergen, and mold spores.  Gaseous pollutants include the vapors from gas cooking stoves, vehicle exhaust, paints and pesticides.    Choosing the best air cleaner depends on the type of allergen causing your individual reactions.  Different air cleaners are better at removing particulate matter from the air while others are preferred for removing gaseous pollutants.

For example, if you are particularly sensitive to dust mite allergen, waking up each morning stuffy and sneezing, you should consider a particulate matter air cleaner in your bedroom.  The EPA has divided them into two types: mechanical and electronic.  Mechanical air filters use a fan to pull air through filters where particles become trapped and cannot escape back into the air. High Efficiency Particulate Air (HEPA) filters fall into this category.

Electronic air cleaners use a process called electrostatic attraction to trap particles.  They also use a fan to draw air in, however the air then passes through a section of the machine where the particles are given an electrical charge.  The charged particles are drawn to a series of flat plates called a collector where they accumulate until the filter is replaced or cleaned.    Although the process is similar, air cleaners called ionizers or ion generators do not have a collector.  They simply charge the airborne particles and expel them back into the air where they attach to nearby surfaces, such as walls or furniture, or attach to one another causing them to settle faster until they can be vacuumed or cleaned up.

If paint fumes or other household odors are bothering you, an air cleaner that removes gaseous pollutants is a better choice.  Gaseous air filters remove gases and odors by using a material, such as activated carbon, to absorb the pollutants.  These filters are typically intended to remove one or more gaseous pollutants from the air that passes through them, but may be specific to one or two types of gas.  It is important to choose an air purifier that is designed to remove the specific gas or odor that is affecting you.

In addition to air cleaners that using a filtering process to remove allergens from the air, there are also systems that will actually destroy pollutants.  Some use ultraviolet (UV) light technology.  These cleaners are called ultraviolet germicidal irradiation (UVGI) cleaners and photocatalytic (PCO) cleaners.  UVGI cleaners use radiation from UV lights that may destroy viruses, bacteria, allergens and mold.  Typically such systems are used in conjunction with an air filtration system.  PCO cleaners use a UV lamp along with a substance called a catalyst that reacts with the light.  They are intended to destroy gaseous pollutants by converting them into harmless products, but do not actually remove particulate matter from the air.

One more type of pollutant destruction system is an ozone generator.  It uses a UV light or an electrical discharge to intentionally produce ozone.  However, as you may know, ozone is a lung irritant that can cause adverse health effects.  Ozone also has little effect in removing most indoor air contaminants, thus are not always the safest or most effective choice.

Filtration

(Mechanical or Electronic)

Air filters Particles Ineffective in removing larger particles because most settle from the air quickly and never reach filters.
Gas-phase filters Gases Used much less frequently in homes than particle air filters. The lifetime for removing pollutants may be short.

Other Air Cleaners

UVGI Biologicals Bacterial and mold spores tend to be resistant to UV radiation and require more light or longer time of exposure, or both, to be killed.
PCO Gases Application for homes is limited because currently available catalysts are ineffective in destroying gaseous pollutants from indoor air.
Ozone generators Particles, gases, biologicals Sold as air cleaners, they are not always safe and effective in removing pollutants. By design, they produce ozone, a lung irritant.

 

Measuring the Effectiveness of an Air Cleaner

The effectiveness of a portable air cleaner, regardless of what you are trying to remove from the air, is measured by the clean air delivery rate (CADR).  Developed by the Association of Home Appliance Manufacturers, the CADR is a measure of the cleaning speed.  Since individual filters vary in their ability to remove different particles, three CADR's for a given device are typically measured: smoke, pollen, and dust.  While an individual portable system may not achieve its rated measure under all circumstances, it does allow comparison between different makes and models.  Typically, the higher the CADR, the more effective the air cleaned will be.  When purchasing a system for your personal use, choose one with the highest CADR for your specific allergy. If you are treating a pollen allergy, consider a purifier with a high CADR for pollen, as stated on the label.

When looking at the CADR ratings, you must also take into account the size of the space in which you will be using your air cleaner.  Portable air purifiers are only meant to clean the air in a single room, not your entire house.  Therefore, if you are having problems at night and when you wake up in the morning, you may want to purchase a particulate matter air purifier specifically for your bedroom.  If you are also concerned about odors in the kitchen, you should consider a gas-phase unit for the kitchen area.  Regardless of what type you choose, you must have an accurate measurement of the square footage and in some cases, the cubic footage for that particular room in order to choose a machine that will be effective.

To calculate your room’s approximate square footage, multiply the length of the room in feet by the width of the room in feet.  To calculate the cubic footage, multiply the length of your space by the width of your space and multiply that by the ceiling height.  Most manufacturers list an optimal square foot area of coverage for their air purifiers, so you'll want to choose a model that is rated to cover the size of your room.  You might also consider choosing a model designed for an area larger than yours for better cleaning at a lower, quieter speed.

Another important measure of unit effectiveness is the cubic feet per minute (CFM) rating. This number represents how many cubic feet of air passes through the unit in any given minute. It gives you an idea of how quickly an air purifier will clean the complete volume of air in your room. Typically, the higher an air purifier's CFM rating, the faster the air in the room will be purified. One more measurement is the air changes per hour (ACH). ACH indicates how many times an air purifier filters the entire volume of air in your space per hour. Those who are looking for relief from allergies and asthma should look for an air purifier that can produce at least 3 to 4 air changes per hour.

Noise Levels

Once you have determined what allergens you need to remove from the air and what size system will work best in your room, there are several ways to narrow down your choice of air cleaner based on your personal preferences.  Noise is an important one, especially if the unit will be used in the bedroom.

Because of the fan element, most air purifiers will emit some amount of noise, depending on the purification speed you choose. Some people need complete silence while sleeping while others enjoy “white noise” in the background.  If noise is a concern to you, look for an air purifier with a decibel (dB) rating for each fan speed. You can compare these ratings to the sounds made by other common household items which in turn will give you a better idea of the level of sound an air purifier will make.

0 dB Hearing Threshold
10 dB Breathing
20 dB Falling Leaves
30 dB Whisper
40 dB Raindrops
50 dB Average Home
60 dB Normal Conversation
70 dB Vacuum Cleaner

While a decibel chart can be helpful, remember that other factors, such as where in the room the purifier is placed, the amount of furniture and choice of flooring can also affect the noise level while the unit is in use.   Many units come with multiple fan speeds.  If noise is a particular concern to you, the option of a lower fan speed may be something to consider.

Other special features that may decrease the amount of noise are a programmable timer and a remote control.  A remote control allows you to turn the unit off and on or change fan speeds without having to leave the comfort of your bed or sitting area.  A programmable timer can be used to automatically turn the system on or off at certain times of the day or night to cut down on noise and to save energy.

In addition, manufacturers offer a variety of other special features to consider when buying an air purifier.  Some offer digital controls for setting fan speeds and timers easily and accurately.  If you think you will be moving your unit from room to room, you might want to look for a one with carrying handles or wheels for easy relocation.  Some systems even come with air quality monitors to sense the level of pollution in a room and filter replacement lights to let you know when to change the filter.

As with any purchase, the more features you opt for, the more likely the cost will increase.  So, in deciding which unit is best for you and your budget, don’t forget to think about maintenance costs.  Look at the cost of replacing filters and how often they need to be replaced in order to get an accurate idea of the true cost of an air cleaning system before buying.  Some brands are designed to need new pre-filters every three months and new HEPA filters every year. Others have filter packs that last up to 5 years.  When filters are not replaced regularly some filtration ability is lost and the motor of the unit could be damaged, so it is important to invest in the maintenance of your unit as well as the unit itself.

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