Best Cheap Air Purifiers

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Price Range
Cheapism $35 - $300
Mid-Range $300 - $500
High End $500 and up

Recent updates

Installing an air purifier is just one of many ways to create a healthier home.

See how your air purifier can combat fall allergies.

Our Picks

lg hamilton beach trueair compact air purifier 04386 250
lg whirlpool whispure ap51030k 250
lg holmes hap242 uc 250
lg winix plasmawave 5300 250
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lg airfree onix 3000 250
lg germ guardian ac4020 3 in 1 250

Hamilton Beach TrueAir Compact Air Purifier 04386 Review

From $48 Best

A permanent "HEPA-grade" filter is the main selling point for this small-room (160 square feet) model. Instead of buying replacements, users vacuum the filter for powerful pollen and dust removal.

Although Hamilton Beach air purifiers don't always see reviews as effusive as the praise showered on higher-end brands, customers can generally rely on the home appliance giant for budget products that work and are designed with affordability in mind. The Hamilton Beach TrueAir Compact Air Purifier, model No. 04386 (starting at $48, Amazon), is a good choice for consumers looking for a basic machine that will fulfill its purpose of improving indoor air quality without requiring large outlays upfront or for future maintenance.

The Hamilton Beach TrueAir Compact Air Purifier has a permanent "HEPA-grade" filter and three fan speeds. It's designed to be effective in smaller rooms of up to 160 square feet, where it can be placed either vertically (like a "tower" model) or horizontally. As opposed to models with "true" HEPA filters (which boast a catch rate of 99.7 percent of particulates as small as 0.3 microns), the TrueAir air purifier can only cleanse the air of 99 percent of particulates smaller than 3 microns. Nevertheless, experts say it should certainly do the job on a majority of the culprits generally cited as the most offending indoor pollutants -- think dust, pollen, pet dander, dust mites, and mold spores. Another plus: This air purifier is small enough to be easily portable and stowed in luggage, for consumers looking for a device to use both at home and at the office or while travelling.

At BestBuy.com, customers give this model an average of 4.3 out of 5 stars. This rating is only slightly lower than those of similar air purifiers we researched that use true HEPA filters. One verified purchaser testifies that this small air purifier managed to maintain the freshness of a home that housed four smokers and a slew of animals, including 20 cats and a monkey. While this appears to be an overachievement (even the reviewer felt the need to assure others it wasn't a joke), many customers are satisfied with this air purifier's ability to remove smoke and common allergens.

Many of the customers who gave this Hamilton Beach model low ratings were simply expecting it to perform better, particularly at removing odors -- which, lacking a charcoal pre-filter, this model doesn't really promise to do. A few reviewers claim that the TrueAir air purifier mitigated smells from litter boxes. Among the nearly 3,000 reviews the product has received on Amazon, there are hundreds asserting that it has helped significantly with indoor and seasonal allergies. One reviewer calls it a "lifesaver" in a household where several members of the family, including grandchildren, are allergy sufferers.

The main selling point of the Hamilton Beach TrueAir Compact Air Purifier is that its HEPA-grade filter supposedly needs no replacing -- which could recoup the initial outlay for the cost of the machine in just one year when compared to similar models, such as the Holmes HAP242-UC, which requires estimated yearly filter replacement expenses close to $30. In terms of maintenance, the filter needs only to be vacuumed regularly and the casings wiped down. It should be noted, however, that a couple of consumers report on Amazon that the filter became damaged after frequent vacuuming and did eventually need to be swapped out.

Whirlpool Whispure AP51030K Review

From $279 Best

Covering up to 500 square feet, this inexpensive air purifier with HEPA and carbon filters boasts an impressive pollen CADR of 401 and makes critics' pick lists alongside models costing hundreds more.

The Whispure line of air purifiers from Whirlpool, the brand known for home appliances, continually receives positive reviews from experts and consumers. The devices are especially noted for their durability. While most cheap air purifiers come with three-year warranties at best, Whispure models remain protected for five years.

Offering 500 square feet of coverage, the Whirlpool Whispure AP51030K (starting at $279, Amazon) is the brand's largest air purifier and boasts solid CADR ratings of 315 for smoke, 325 for dust, and 401 for pollen (experts recommend about two-thirds of the coverage area). This air purifier has a three-step filtration system: An internal fan moves air through the pre-filter to capture large particles, the air is deodorized by the carbon filter, and remaining microscopic allergens are captured by a HEPA filter. There are four fan speeds, as opposed to the standard three found on many inexpensive air purifiers, including a turbo setting ideal for launching high-powered attacks on airborne pollutants. A filter change indicator conveniently notifies users in advance to ensure that replacements will be on hand when needed to keep the unit working at optimal efficiency.

When tested by consumer product experts, the Whirlpool Whispure AP51030K has scored very high for its ability to remove smoke, dust, and pollen, even at its lowest speeds. Customer reviews on Amazon, Walmart, and Sylvane.com, a retail site that specializes in air quality products, confirm these findings. Many praise this model for ridding their homes of cigarette fumes or even wildfire smoke. Several were impressed to see the fan visibly removing dust particles and pet hair from the air. Scores of allergy sufferers credit this machine with notable improvements in symptoms of indoor allergies.

For the most part, disappointments focus on the unit's charcoal filter, which some reviewers found less effective at removing unpleasant smells from their homes as they would have liked. Experts say this model is meant to handle only light odors.

The main drawback of this relatively inexpensive machine is that the manufacturer recommends annual replacement of the HEPA filter, which can cost as much as $100, and the carbon filter is to be changed out every three months (we saw packs of four for about $30). These outlays are rather on the high side -- even more so than replacement costs for some more expensive units. But given the comparatively low upfront cost and demonstrated longevity of the machine, the Whirlpool Whispure AP51030K remains an excellent value overall. It's also Energy Star qualified, so it should be slightly easier on your electricity bill.

Holmes HAP242-UC Review

From $36 Good

This low-budget buy for small rooms up to 109 square feet features multiple filter options, including one that catches up to 99.99 percent of particles larger than 0.3 microns, and an optional ionizer.

Cheapism previously listed the Holmes HAP242-UC (starting at $36, Amazon) as one of the best cheap air purifiers, and recent upgrades to the available filter choices make it even more attractive, although the competition this year is stiffer. The Holmes HAP242-UC is designed for spaces up to 109 square feet, making it ideal for an office or small room. It claims a smoke CADR of 70, which is a decent but not great number for its coverage range. The low price includes an optional ionizer, a function that many see as a boon but may be best avoided given the potential health risks of ionization technology (see our buying guide for further details).

The Holmes HAP242-UC now caters to a much wider range of air-cleansing needs with a full line of specialized AER1 filters, which range from a standard HEPA-type model to an "Allergen Performance Plus" version that takes HEPA technology one step further and promises to cleanse indoor air of 99.99 percent of particles as small as 0.3 microns. All the filters are supported by carbon pre-filters to absorb smoke and help neutralize odors caused by pets, cooking, and other sources. The HAP242-UC gets particular credit for its ability to deal with tobacco fumes, with one user saying that it almost miraculously made life with a chain-smoking grandmother bearable for her young daughter.

Even without opting for the more advanced, more expensive filter replacements, the Holmes HAP242-UC seems to handle dirt and allergens in the air fairly well. It was clear that many consumers who reviewed the product on Amazon had no idea that this model can be fitted with a true HEPA filter, and nevertheless there were scores who reported that the air purifier provided relief from stuffy noses, sneezing, and other breathing difficulties caused by pet or seasonal allergies. More than few reviewers noted that this Holmes model picks up huge amounts of dust. The manufacturer recommends replacing the less finely meshed HEPA-type filters every four months.

Given how many reviews comment that the small size of this unit makes it ideal for keeping next to the bed to help ease nighttime congestion, one might assume the Holmes HAP242-UC is a relatively quiet operator. Yet there are many complaints of noise from this model, even on lower settings, and frequent references to the "white noise" created by this machine. Whether you expect to find these sounds soothing or otherwise, know that this model's presence in your home will not be entirely unobtrusive.

Be warned that at least three customers have posted on Amazon that their particular units caught fire or parts of the plastic casing melted. None of these reviewers explained the specific circumstances, however, and there have been no recalls of the product or widespread reports that it poses a fire hazard. Perhaps these were faulty units or poorly maintained. Given that this model collects so much dust, and many users run it 24 hours a day, it's important to keep it clean and follow proper guidelines and suggested timeframes for filter replacement -- even as the ongoing expense adds up. Ironically, it could cost more to go with the "HEPA-type" filters that need to be replaced more frequently than a true HEPA filter with a 12-month usage window.

Winix PlasmaWave 5300 Review

From $168 Good

Made for rooms up to 350 square feet, this Korean-designed model couples a HEPA filter with a carbon pre-filter and advanced technology. It's big on energy efficiency while tackling tiny pollutants.

Although the South Korean brand Winix is a relative newcomer to the U.S. market, its air purifiers have earned high praise from experts and receive very positive reviews. The Winix PlasmaWave 5300 (starting at $168, Amazon) is a top performer -- the brand's best-selling model. This four-speed, Energy Star-certified unit with a true HEPA filter, as well as carbon pre-filter, uses patented PlasmaWave technology to break down air pollutants and odors. The company worked with researchers at Drexel University to develop this cutting-edge cleaning system. Yet despite the high-tech functionality of the Winix PlasmaWave 5300, the manufacturer created this unit with an eye toward keeping the price relatively low. Stripped of a few of the "extras" found in more recent models (most notably, a remote control), this one still delivers powerful performance that at least one tester claims is pretty much comparable to that of its updated, remote control-touting cousin, the Winix PlasmaWave 6300.

At 16.3 inches wide and 21.7 inches high, this relatively large air purifier is designed for big rooms up to 350 square feet. The unit's CADR ratings are in keeping with this coverage area: a solid 235 for smoke, 216 for dust, and 251 for pollen. It also features a sleep mode, an electronic display, and an automatic sensor that can cycle the unit through three stages of cleaning based on changes in room air quality.

Reviews on Amazon, which number nearly 1,000, are very favorable toward this model. Across these reviews, the Winix PlasmaWave 5300 is noted as effective for relieving common allergy symptoms. Countless reviewers write of stuffy noses being cleared, trouble breathing lessened, and allergy symptoms alleviated. The Winix PlasmaWave 5300 has scored points for smoke removal, as well, with several reviews mentioning that it quickly clears out rooms well enough to calm smoke detectors. Several also note that the machine's odor-sensing abilities are extremely sensitive, and it kicks into the most powerful mode the minute it sniffs anything amiss. At the same time, some complain that the noise emitted at high power levels is slightly unpleasant.

It's also worth noting that, although the PlasmaWave technology is not supposed to produce any ozone byproducts, which can be harmful to health, there is still some debate as to whether it's completely ozone-free. While any emissions it may be producing are within government safety limits, and much lower than those released by ionizing air purifiers, consumers may choose not to use the "Wave" function on the machine and simply rely on the HEPA filter to do the trick. (A reviewer explains how to turn off this function without the benefit of a remote control.)

Finally, although consumers save on energy costs with this efficient model, it still requires periodic spending on filter replacements. The Winix PlasmaWave 5300 is equipped with a light to signal it's time for a change. A few users express dissatisfaction with models requiring more frequent filter changes than originally recommended by the manufacturer.

Envion Ionic Pro Turbo Review

From $135 Think Twice

With a large coverage range (500 square feet) and relatively low cost, this unit may seem like a bargain, but for the questionable efficacy and potential health risks of air ionizers.

The Ionic Pro Turbo from Envion (starting at $135, Amazon) is less than half the cost of popular ionic air purifiers such as Sharper Image’s Ionic Comfort Quadra. With its low price and an ideal coverage range for small apartments -- up to 500 square feet -- this is an attractive option for many consumers. A slim, black tower design makes it less obtrusive and more "stylish" than bulkier models that cover a similar size area.

While reviews traditionally mention “white noise” and complain about more intrusive rattling from air purifiers with filters and fans, the technology employed by the Ionic Pro Turbo is completely silent. It relies on ionization to electrify and capture a claimed 99.9 percent of airborne pollutants greater than 1 micron in size. In customer reviews on the Walmart website, the Ionic Pro Turbo garners an average of 4.2 stars out of 5 and is frequently recommended for use in bedrooms and other areas where quiet is desired. Several reviewers express amazement at the amount of gunk the purifier collects on its blades, and many credit the machine with alleviating allergy symptoms and breathing difficulties (one used it while recuperating from lung surgery).

Because it doesn't use filters, the Ionic Pro Turbo doesn’t incur the ongoing maintenance costs associated with regular replacement. Even when holding up this model against similar ionic air purifiers, many reviewers point to the front-loading collection blade, which doesn’t require a lengthy and intricate process to remove accumulated dirt and debris from its blades. The Ionic Pro Turbo also displays an alert and automatically shuts down when it requires deep cleaning.

Attractive, affordable, easy to clean, and easy on the ears -- it sounds almost too good to be true. And, indeed, there may be more than a few catches here. Ionic technology is not without its foibles, as discussed at length in our air purifier buying guide. Although ionic air purifiers adhere to government safety standards, they are known to emit low levels of ozone, a potential health risk. There are also questions about their effectiveness at removing significant amounts of pollutants from the air, as a great deal of the residue not captured by the blades tends to settle on walls and furniture, creating stains. For this model in particular, there are enough reports on Amazon and elsewhere of faulty models that broke down soon after initial use to give us pause. In the final assessment, it seems that consumers get both more and less than they bargained for with the Envion Ionic Pro Turbo.

Buying Guide

According to the EPA, Americans spend 90 percent or more of their time indoors, where the quality of the air is generally far worse than outside. For those who suffer from asthma and allergies, or are plagued by pet and smoke odors, an air purifier can make a dramatic difference in the levels of irritant exposure in homes and offices. The air purifier market is growing, with new brands entering the mix and new technologies emerging at a steady rate. With many high-end brands such as IQAir, Blueair, Austin, and Alen well outside of the price range of the average consumer, we've done the research to round up cheap air purifiers from trusted appliance brands and more affordable specialty companies to help clean up the air without cleaning out your wallet.

Cheap Air Purifier Buying Guide

Medical experts warn that not even the very best air purifier can make any health claims whatsoever, and the EPA bluntly advises that air purifiers be only part of an air treatment plan that includes controlling the source of pollutants and improving ventilation. Still, experts and consumers generally agree that these devices (if they perform well) should improve air quality. In air purifier reviews, many consumers with allergies or trouble breathing say air purifiers offer some relief as they work to rid the air of many of the contaminants, both visible and invisible, that contribute to these problems.

The biggest factor affecting the price of an air purifier is the amount of square footage it's designed to cover. Room air purifiers are designed either for small rooms (less than 200 square feet) or large rooms (200 to 600 square feet or more). An air purifier meant for 150 square feet will always be cheaper than an air purifier meant for 550 square feet, regardless of features or performance. Many rooms straddle the line between small and large, so err on the side of large when considering what size air purifier to buy.

Cheap small-room air cleaners range in price from $35 to $60 while high-end purifiers for small rooms can cost more than $300. Our top picks in the budget range, the Hamilton Beach TrueAir Compact Air Purifier 04386 (starting at $48) and Holmes HAP242-UC (starting at $36), are not only reasonably priced but have stood the test of time, with thousands of reviewers attesting to their performance.

Cheap large-room air purifiers generally start at about $150 and top out at $300. In this segment we chose the Whirlpool Whispure AP51030K (starting at $279), which is designed to cover up to 500 square feet, and the Winix PlasmaWave 5300 (starting at $168), designed for spaces up to 350 square feet. The Envion Ionic Pro Turbo (starting at $135) comes at a price almost unbelievably low for a unit that claims to provide 500 square feet of coverage. But this widely visible brand seems to suffer from generally shoddy workmanship, according to reviews, and the safety and effectiveness of its ionizing technology have been questioned.

Upmarket models start at about $500, while some of their costlier cousins run to $1,000 and beyond. They are more powerful, generally cover larger square footages, and feature technologically advanced filters, along with conveniences such as remote controls and LED displays. Our picks may not have some of the bells and whistles of these high-end machines, but what they do have are the endorsements of both experts and consumers, many of whom would place them side by side with much pricier models.

Shoppers will not spy many of our top picks in the aisles of big-box stores such as Walmart and Target. They are most readily found and generally cheapest online at Amazon. A version of the Hamilton Beach 04386, for example, is primarily sold via Amazon with an "A" at the end of the model number.

Finally, in case there is any question, know that an air purifier, no matter how expensive, will not remove radon or carbon monoxide from the air. These toxins are extremely dangerous and the latter can be lethal. Consumers who suspect they may be at risk for radon gas exposure can buy a testing kit -- if harmful levels are found, call in a pro. A carbon monoxide alarm can detect the otherwise odorless and colorless gas sometimes called the "silent killer."

Features Comparison Buying Guide continues below table

What We Looked For

For consumers just beginning a search for a cheap air purifier, the first step is identifying the air quality issue(s) they want to address. Common irritants include smoke, dust, pet dander, pollen, mold, cooking and perfume odors, and chemicals and gases. After doing your best to control the source of the problem and increase ventilation, determine the size of the space you'd like to address and consider which type of cheap air purifier will complement your overall line of attack. The Environmental Protection Agency dedicates an entire section of its website to the topic of indoor air quality and discusses the performance characteristics of different types of air purifiers. Some cheap air purifiers focus more on particulates than on odors or gases, or vice versa.

HEPA Air Purifiers.

High-efficiency particulate air filters resemble the lint screens used in clothes dryers, except that they are made of small, tightly woven fibers (often glass) as opposed to metal or plastic. HEPA filters, found in the Whirlpool Whispure AP51030K and Winix PlasmaWave 5300 large-room air purifiers, trap 99.97 percent of airborne particles -- think dust, pollen, mold spores, pet dander -- as small as 0.3 microns (1 micron equals 1/25,400 of an inch).

The Hamilton Beach TrueAir 04386 model for small rooms uses a HEPA-grade filter, a step down from a true HEPA filter. These filters can claim to capture only 99 percent of airborne particles -- those at least 3 microns in size. Still, reviewers hold that the Hamilton Beach is an absolutely viable choice for mild or seasonal allergy sufferers. As a buyer's guide on the retail site AchooAllergy.com illustrates, pollen, plant spores, dust mite allergens, mold, and certainly most dog hair and cat dander are large enough that even a pseudo HEPA filter should be able to trap them.

For consumers who insist on a true HEPA purifier for a small room, the Holmes HAP242-UC has recently been outfitted with a new range of filters that let users to decide the level of allergen and odor protection they need, from HEPA-type to an even more advanced HEPA-Plus filter that claims to attack 99.99 percent of the smallest particles. If fighting the spread of viruses is a main concern, the Germ Guardian AC4020 (starting at $55) is not only one of the cheapest and most attractive small room units with a HEPA filter, it also uses ultraviolet germicidal irradiation to destroy bacterial microorganisms.

The Airfree brand offers an alternative approach in the Airfree Onix 3000 (starting at $266). Its Thermodynamic Sterilizing System uses a ceramic core to kill off offending spores, fungus, viruses, and bacteria, at temperatures of 400 degrees Fahrenheit. With no fan and no filters to replace, this model is silent and eco-friendly. The patented technology works slowly, however, claiming to reduce 70 percent to 90 percent of organisms in the air within 10 days.

Keep in mind that airborne particles often settle before being drawn into an air purifier, so even a HEPA filter won't get rid of all airborne pollutants. Before buying an air purifier, note any information on air changes per hour, or the number of times air flows through the filter each hour. The higher the ACH, the more opportunity to catch pollutants. Many experts recommend a minimum of four. The two HEPA air purifiers on our list of top picks, the Whirlpool Whispure AP51030K and Winix PlasmaWave 5300, meet this minimum at 4.8 and 5 pass-throughs an hour, respectively. The specs for the other units we researched don't include this information.

Carbon Pre-Filter.

Many HEPA air purifiers also incorporate a carbon pre-filter that helps absorb odors and trap some larger particles. If smoke and/or odors are the primary problem, a cheap air purifier with a carbon filter (sometimes referred to as a charcoal filter) is a good choice. This type of filter uses activated carbon to absorb the offending fumes but doesn't remove other microbes from the air. That's why a carbon filter is often paired with a HEPA filter. Among the multiple filters available for the Holmes HAP242-UC, the AER1 Odor Eliminator boosts a true HEPA filter with doses of carbon, zeolite, and baking soda for even greater odor absorption.

The carbon filters in most cheap air purifiers are not equipped to remove volatile organic compounds, which are often byproducts of common household cleaning agents, as well as paints, varnishes, waxes, and certain building materials, among other substances. The activated carbon levels in the filters are not high enough to eliminate VOCs. For a serious problem with these gaseous pollutants, look for an air purifier recommended especially for this purpose, and expect to pay more than our $300 limit.

No Ozone Generation.

The most controversial air purifiers intentionally convert air molecules into ozone to tackle odors. The EPA warns that ozone can seriously damage the lungs and, at the very least, exacerbate respiratory problems. Consequently, many experts recommend against ozone-generating air purifiers.

Ionic air purifiers such as the Envion Ionic Pro Turbo (an electrostatic precipitator, to be exact) also produce small amounts of ozone, but supposedly at levels that do not exceed current safety standards (and do nothing to cleanse the air). Instead of using a filter, ionic air purifiers catch contaminants on electrically charged plates/blades or cells. They send out negatively charged ions that attach to airborne particulates, which are then pulled down out of the air and lured back to a positively charged collector plate. Reports dating back to at least 2003 have questioned the efficacy of air ionizers -- most famously the Ionic Breeze, resulting in a lawsuit that forced manufacturer Sharper Image to file for Chapter 11 bankruptcy. And yet, these types of purifiers remain popular with some consumers and are readily available at many retailers.

Perhaps the amount of dust, dirt, and grime visible on the collection blades makes an ionic air purifier appear to be doing its job. But the silent operation that makes these models appealing depends on the absence of a fan, which means the machine catches only the contaminants that happen to drift within close range. So what happens to the rest? Experts note that often the particles on the charged plates also may be recirculated, and some wind up settling on other surfaces.

Given the potential safety risks and many viable alternatives, our inclination is to avoid products such as the Envion Ionic Pro Turbo. The Holmes HAP242-UC is augmented with an optional ionizer, for consumers who really want to give this technology a shot. The Winix PlasmaWave 5300's "corona discharge" process supposedly emits very low levels of quickly dispersing ozone when switched into PlasmaWave mode. Consumers can keep the setting turned off should they decide not to risk exposure to any ozone whatsoever.

High CADR.

An air purifier's clean air delivery rate should correlate with the size of the room(s) where the product will be used. There is a CADR for three types of pollutants -- tobacco smoke, pollen, and dust. Each is determined separately by the Association of Home Appliance Manufacturers, an independent third party, as part of a voluntary program. The numbers are listed on the packaging for participating products, including some but not all of our picks. The maximum CADRs, based on the testing protocols, are 400 for dust and 450 for pollen and smoke. AHAM recommends looking for a CADR for tobacco smoke that's at least two-thirds the square footage of the room where the air purifier will be used. The smoke CADR for the Whirlpool Whispure AP51030K, for example, is 315, making it suitable for larger rooms (about 475 to 500 square feet). An air purifier with a higher CADR relative to the room size will clean the air faster and more often.

Air Purifier Reviews

Determining which model is right for you based on air purifier reviews by users, especially at the lower end of the price spectrum, can be frustrating. As with many consumer products, the first review you read might be glowing and the next one damning: One user deems a particular model a waste of money because it's too noisy or hard to maintain while another says it makes a big difference in the breathability and smell of the air. We also noticed that models meant for large rooms generally garner more favorable comments than small-room air purifiers. Although there aren't many slam-dunks in this category, our picks, large and small, are generally well-received by consumers and experts alike.

Pollutant Removal.

Judging the performance of an air purifier starts with the simple question of whether or not it cleans the air. Among our top picks, the Hamilton Beach TrueAir Compact Air Purifier -- our first choice in the small-room category -- is the only one without a "true" HEPA filter. Despite this, it receives highly positive feedback on Amazon from a majority of reviewers, who number in the thousands. A good portion report noticeable differences in dust levels and say the air purifier mitigates allergy symptoms and reduces pet odors.

The best large-room air purifier on our list, the Whirlpool Whispure AP51030K, handily vanquishes the usual airborne irritants and also seems to have good staying power, with several reviewers reporting no hitches in operation after many years of ownership. Countless reviews on Amazon say it takes care of the smoke and smell from cigarettes or cigars, and several even laud it for clearing the air during wildfires. Any room air purifier does a better job when placed in a spot where the air can freely circulate, with the door and windows closed.

Opinion is sharply divided on the Envion Ionic Pro Turbo. While some reviewers are enamored of it, others express doubts about whether it actually cleans the air, and we saw several references to an "ozone smell" given off by the machine. These are standard criticisms usually associated with air ionizers and could be considered subjective. More worrisome are numerous complaints on Amazon and the Walmart website regarding these units breaking down after only limited usage.

Noise Level.

One important thing to remember about noise is that one person's white noise is another person's distraction. Most air purifiers have three speed settings and those with fans are the noisiest. Users report that the lowest setting is the least intrusive, although this reduces the rate at which air is circulated. The Whirlpool Whispure AP51030K gets several nods of approval from reviewers on Amazon for very quiet operation, even on the turbo setting. Both the Hamilton Beach and Holmes small-room models also win some plaudits for relatively quiet operation, while many find the Germ Guardian AC4020 surprisingly loud.

The Winix PlasmaWave 5300 is equipped with a sleep mode that many reviewers say virtually reduces all noise. Controversial ionic air purifiers and the Airfree Onix 3000, with its specialized heat technology, are made to be totally silent.

Ongoing Expenses and Maintenance.

It would be great if an air purifier could be purchased, plugged in, and left alone. Much to the chagrin of reviewers, HEPA air purifiers demand two ongoing expenses: energy and, more significantly, replacement filters.

To cut the energy cost, which corresponds to the size of the air purifier and the frequency with which it's used, experts recommend using the lowest setting (most come with three -- high, medium, and low) and leaving the machine off when you don't need it. Ionizing room air purifiers such as the Ionic Pro Turbo, as well as units such as the Airfree Onix 3000, consume less energy but are meant to run continuously.

The Hamilton Beach TrueAir Compact Air Purifier has a permanent filter that requires only vacuum cleaning. On the other models, both the primary filter and the carbon pre-filter (if there is one) must be replaced regularly. The HEPA filters on many room air purifiers should be changed at least every 12 to 18 months, although some users report replacing filters as often as every three months. The carbon pre-filter on a cheap air purifier lasts three to six months. Depending on the specific size and model, replacement filters for the models we've covered cost about $30 to $115 dollars a year. The Whirlpool Whispure AP51030K features two indicator lights to remind the user well in advance when the filters need to be changed. The Germ Guardian AC4020 likewise has a replacement timer.

Reviews on Amazon gripe that the Holmes HAP242-UC collects enormous amounts of dust, and Holmes says its less finely meshed AER1 HEPA-type filter should optimally be replaced at least four times a year. Some users get around this expense by removing and cleaning filters, whether by vacuuming, wiping with a damp cloth, or soaking in water. Many carbon filters are also washable, and do-it-yourself types report finding generic charcoal pre-filter material at home improvement stores.

The Airfree Onix 3000 stands out when it comes to maintenance, because there's no filter to clean or replace. All users have to do is dust the outside from time to time. The steel plates (and charging wires) or the collection cell on an ionic air purifier such as the Envion Ionic Pro Turbo must be kept clean to work at maximum efficiency. Dirty plates make popping and crackling noises. These catchments should be wiped down with a damp rag periodically, and some models need this attention as often as every four to five days.

Additional Products We Considered

Airfree Onix 3000 Review

From $266

Filterless and offering an amazing cost-to-coverage ratio, this model uses proprietary technology to destroy microorganisms with ultra-high heat before returning air into rooms up to 650 square feet.

For a fairly low price, the Airfree Onix 3000 (starting at $266, Amazon) boasts coverage for areas up to 650 square feet; ease of use (just plug it in and walk away); low operating costs; and eco-friendly technology for attacking germs, mold, pollen, mildew, and other allergy offenders lurking in the air.

Airfree uses a patented Thermodynamic Sterilizing System said to remove 99.99 percent of microorganisms from the air. Essentially, air is drawn into the unit by convection, then subjected to 400-degree heat, which immediately incinerates any microorganisms present. The cleansed air is cooled and sent back out into the room. The process is pretty safe and simple, but not without its flaws.

An expert review on the retail site Allergy Buyers Club notes one big drawback of the purification process: Because it targets organic pollutants and uses no fan or filters, it doesn't combat chemical pollutants or odors caused by these sorts of substances. Also, there’s no “turbo” switch here. It takes a recommended seven to 10 days of continuous usage, if not a month, to get optimal results out of this air purifier. Good thing it's silent and relatively small, with a pod-like design that helps it blend into the background. A blue “nightlight” on top keeps users from tripping over it in the dark.

Perhaps not surprisingly, given the novelty of Airfree's TSS technology, user reviews for the Airfree Onix 3000 are more than a little mixed. Many negative reviews onAmazon come from buyers who insist they can't even tell if the air purifier is working. And it does seem as if more than a few of the reviewed units were duds. On the other hand, positive user reviews on Amazon are effusive, and the Airfree Onix 3000 has earned an average of 4.6 out 5 stars from nearly 60 Allergy Buyers Club customers. Some reviewers say they’ve seen dramatic improvements in their allergy symptoms and breathing overall.

Germ Guardian AC4020 3-in-1 Review

From $55

This sleek, small-room unit (93 square feet) combines a HEPA and carbon filter in one to reduce replacement costs. The third player in the purification process: a UV sanitizer.

Although there are precious few Germ Guardian AC4020 reviews online, the fact that parent company Guardian Technologies has a difficult time keeping the model in stock suggests sales are high. And there are a lot of reasons to believe this little air purifier would be coveted by consumers.

First, at only a little more than 7 inches high, the AC4020 (starting at $55, Amazon) is an ideal size to be placed on a desk or bedside table. There’s also a lot of potential air-cleansing power packed into this small-room model, which covers areas up to 93 square feet. The AC4020 is armed with a combined HEPA-charcoal filter that attacks odors as well as 99.97 percent of particles larger than 0.3 microns in size. This "3-in-1" model also employs the latest in UV technology to further sanitize the air and kill germs, viruses, and bacteria. Additional features include three fan settings, a filter-change indicator, and an aesthetically pleasing design. Unlike many other air purifiers, the Germ Guardian AC4020 is meant to be proudly displayed, not stashed in a corner.

Of the few reviews on Amazon, those from customers unhappy with their purchases cite the fact that the AC4020 is a lot noisier than they expected given its diminutive size. In an extended 4-star review, however, one buyer insists that the sound issue is pretty much the only thing that can be criticized about this model, which in all other ways is well worth the relatively small amount of money spent. (Use it on the lowest setting to minimize noise.) The design allows users to save on filter replacement costs, as it requires only a single filter (selling for about $15) to be changed at six-month intervals, rather than separate HEPA and charcoal filters. Taking all that into account, this little black box seems like a bargain.