What is Air Purifier?
An air purifier or air cleaner is a device that removes contaminants from the air in a room to improve indoor air quality. These devices are commonly marketed as being beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke.
The commercially graded air purifiers are manufactured as either small stand-alone units or larger units that can be affixed to an air handler unit (AHU) or to an HVAC unit found in the medical, industrial, and commercial industries. Air purifiers may also be used in industry to remove impurities from the air before processing. Pressure swing adsorbers or other adsorption techniques are typically used for this.
The best ways to improve indoor air are to remove the pollutant sources and ventilate with clean outdoor air. Room air purifiers can help when those methods are insufficient or not possible.
Room air purifiers are designed to filter the air in a single room, not the entire house, like a whole house system tied into the home’s heating, ventilating, and air conditioning system. And while they do help to reduce indoor pollution, there are limits to what they can do.
What Air Purifiers Do Well?
The air purifiers that do well in our tests proved in our labs to be good at filtering dust, smoke, and pollen from the air. Multiple studies of room air purifiers show that results in reductions of 50 percent or higher in particulate matter. In one 2018 study of about 130 households, filtration resulted in about 30 percent reduction in coarse particles, like dust.
But how does that affect health? Almost a dozen studies including ones conducted in Vancouver, British Columbia; Taipei, Taiwan; and Massachusetts looked at cardiovascular effects and showed improved cardiovascular health among participants.
The EPA’s review of eight studies focused on allergy and asthma symptoms and showed modest improvements in at least one health area, such as some allergy symptoms (which vary from person to person). And asthmatic participants in a 2018 study by the University of California, Davis (PDF) reported a 20 percent reduction in-clinic visits.
Still, the scientific and medical communities can’t definitively link the use of air purifiers to health benefits because reported health benefits are inconsistent among participants and there have been very few long-term studies.
Plus, some studies had other variables at play, such as the regular use of a vacuum cleaner (CR can help you choose one of those, too), pillow covers, and the removal of pets from the bedroom, all of which can affect results.
As for the coronavirus, air purifiers are capable of capturing the droplets that the coronavirus travels in (when people cough, talk or breathe). But you’ll need one that consistently draws in enough air to reduce virus particles.
What Air Purifiers Don’t Do?
An air purifier can remove allergens only while they’re floating in the air. Larger, heavier allergens, such as mites, mold, and pollen, settle to the ground so quickly that the air purifier can’t capture them in time.
What We Don’t Yet Know?
Radon is another blind spot for air purifiers and other air cleaners, according to the EPA; studies are inconclusive on-air purifiers’ ability to tackle this dangerous gas. And in fact, there is insufficient research on air purifiers that address gaseous pollutants as a group, so it’s unclear how effective air purifiers are.
There is also limited data on the effect of ionizer air purifiers on health. That brings us to another important consideration: the various kinds of air purifier technology available.
How do air purifiers work?
Air purifiers usually consist of a filter, or multiple filters, and a fan that sucks in and circulates air. As air moves through the filter, pollutants and particles are captured and the clean air is pushed back out into the living space. Typically, filters are made of paper, fiber (often fiberglass), or mesh, and require regular replacement to maintain efficiency.
That means, in addition to the purchase price of an air purifier, you should also factor in operating costs and filter replacement costs. Operational costs can easily amount to $50 annually since you should be running air purifiers near constantly to garner the benefits. Filter replacements can run upwards of $100 a year all told.
Types of Air Purifiers
There are several technologies air purifiers employ for tackling indoor pollution. Some work better than others. Some can actually be bad for your health.
1. Mechanical filters
This is the type we test. Air purifiers with pleated filters use fans to force air through a dense web of fine fibers that trap particles. Filters with very fine mesh are filters certified to collect 99.97 percent of particles of a certain size.
As for limitations, mechanical filters don’t help with gases or odors. And they can be expensive to maintain. Mechanical filters need replacing every six to 12 months; they can cost up to $200 per filter but typically max out at $80.
2. Activated carbon filters
Rather than catch particles like mechanical filters, sorbent filters use activated carbon that can adsorb some odor-causing molecules from the air. They may also tackle some gases, but they’re not particularly effective against formaldehyde, ammonia, or nitrogen oxide.
Because they don’t combat particles, many air purifiers will have both an activated carbon filter and a pleated filter for catching particles.
Activated carbon gets saturated faster than a pleated filter, though, and requires replacement more frequently every three months, as opposed to every six to 12 months for pleated filters. And be prepared: Activated carbon filters cost up to $50 each.
CR does not currently test for odor removal, but we did conduct a one-off test in 2008 with five air purifiers that came with odor-removing claims. For this test, we assessed how well these machines removed cooking odors. The results: Only two devices were able to do so because they used very large and thick carbon filters.
3. Ozone generators
These machines produce ozone, a molecule that can react with certain pollutants to alter their chemical composition. This can result in dangerous indoor air quality, and CR does not recommend these types of air purifiers.
Makers of ozone generators often claim that the devices emit safe levels of ozone, but in the past, our tests found that even at low settings, some ozone generators quickly exceeded the Food and Drug Administration’s limit of 0.05 parts per million for medical devices.
Plus, studies reviewed by the EPA have shown that low levels of ozone the chief ingredient of smog don’t effectively destroy indoor pollutants. Studies also show that ozone has been linked to decreases in lung function and increased risks of throat irritation, coughing, chest pain, and lung tissue inflammation. Ozone might also worsen asthma, emphysema, and bronchitis, according to the EPA.
4. Electronic air purifiers
Electrostatic precipitators and ionizers charge particles in the air, so they stick to plates on the machine or to nearby surfaces by a magnetic-like attraction. CR doesn’t typically test them or recommend them because they can produce ozone.
5. Ultraviolet germicidal irradiation (UVGI)
Some manufacturers claim their air purifiers kill airborne viruses, bacteria, and fungal spores with UV lamps. But some bacteria and mold spores are resistant to UV radiation.
To work, the UV light must be powerful enough and the exposure must last long enough—minutes to hours rather than the few seconds typical of most UVGI air purifiers—to be effective. CR does not test UVGI technology, though some mechanical air purifiers we test may have the function.
6. Photocatalytic oxidation
PCO uses ultraviolet radiation and a photocatalyst, such as titanium dioxide, to produce hydroxyl radicals that oxidize gaseous pollutants. Depending on the pollutant, this reaction can sometimes generate harmful byproducts, such as ozone, formaldehyde, nitrogen dioxide, and carbon monoxide.
CR does not currently test PCO technology. There have been few field investigations done on the effectiveness of PCO air purifiers, but one laboratory study conducted by researchers at Syracuse University in New York reported that the devices did not effectively remove any of the volatile organic compounds (VOCs) typically found in indoor air.
A variant of PCO known as PECO emerged more recently from the manufacturer Molekule. We tested the air purifier, and it did not fare well in our tests for dust, smoke, and pollen removal.
What to Consider While Shopping for an Air Purifier
1. Cost of replacement filters
As a general rule, you should replace filters (or clean those that can be cleaned) every six to 12 months for pleated filters and every three months for activated carbon filters. Most of the units we tested have an indicator that lets you know when to change (or clean) the filter.
The costs of filters vary widely, but in our tests of large air purifiers, they range from $20 to more than $200 a pop. Filters with odor-removing carbon can cost as much as $50.
There are a couple of labels you may want to look for on the packaging. The first one is the Energy Star logo. Air purifiers must run around the clock to be effective, and you should factor in the energy cost when you shop. Energy Star certified purifiers are 40 percent more energy-efficient than standard models.
You may also see an AHAM Verified seal, which means that the Association of Home Appliance Manufacturers has tested the model. Many air purifiers have undergone AHAM’s voluntary certification program, which provides clean air delivery rates (CADRs) and room size guidelines on the seal.
CADR reflects, in cubic feet per minute, the volume of clean air that an air purifier produces on its highest speed setting. For example, a purifier with a CADR of 250 for dust particles reduces particle levels of dust to the same concentration that would be achieved by adding 250 cubic feet of clean air each minute.
The higher the CADR, the faster and more efficient the air purifier is. Room air purifiers often achieve the highest CADR. In our tests, a CADR above 240 gets an Excellent rating; 240 to 180, Very Good; 179 to 120, Good; 119 to 60, Fair; and anything under 60 earns a rating of Poor.
There are different CADR ratings for removing tobacco smoke, dust, and pollen. Focus on the CADR for your main pollutant of concern. For instance, if you live with a smoker or use the fireplace regularly, choose an air purifier that has a high CADR for tobacco smoke.
3. Room size
If an air purifier has an AHAM Verified seal, you can trust that the unit can handle the suggested room size listed on the seal. Be wary about manufacturers’ claims, though. We have tested many air purifiers that are not suitable for their claimed room sizes.
You can check our ratings to see what room size range we suggest for each model based on its test results. Also, consider sizing up. Most of the models that are suitable for large rooms (350 square feet and up) still work well at lower (quieter) speeds, which is nice for when you’re watching TV or sleeping.
Judge an air purifier not just by how well it performs but also by how well you’ll be able to live with it. These machines should always be running, so ideally, they should also be quiet. (For reference, a noise rating around 50 decibels is roughly equal to that of a refrigerator.)
You may be able to find how many decibels a model operates on its packaging or website listing before you buy. Or check our air purifier ratings; we rate models on noise levels at high-speed and lower-speed settings.
Other tips for minimizing noise from an air purifier: Run the unit on the high setting when you’re not in the room and turn it down to low when you’re nearby. Or buy an air purifier certified for a larger area so that even at a low speed, it filters more air.
How to Get the Most Out of Your Air Purifier
Clean or replace filters regularly. As a general rule, you should replace them (or clean those that can be vacuumed) every six to 12 months for pleated filters and every three months for carbon filters.
Place it wisely. If you have just one unit, place it in the room where you spend the most time. For most people, that’s the bedroom. These machines can be heavy and clunky to move around, so if you want an air purifier in multiple rooms, you may want to buy a unit for each room.
Make sure to place the air purifier in a spot where nothing can obstruct airflow—away from curtains, for instance. For more, read our article on the best and worst air purifiers of 2021.
Keep your purifier running 24/7. And keep doors and windows closed while it’s in use. We suggest running the unit on the high setting when you’re not in the room and turning it down to low when you’re nearby. Or buy an air purifier certified for a larger area so that you can run it on a low speed and still have it work effectively.
Can air purifiers filter the outdoor air that enters your home?
Sometimes, non-organic air pollutants like the VOCs we mentioned previously can originate from outside your home. “There are all sorts of scenarios in structure fires where large doses of smoke inhalation may lead to cyanide toxicity.
But that would largely need to be someone who was standing directly in or near the fire: Those people are brought to emergency rooms immediately,” Dr. Roten explains. “Generally, outside pollution or smoke or temporary bad air isn’t a constant concern for bystanders.”
But the right kind of purifier can address any environmental air qualities in your locale. Using nearby wildfires as an example,
So… should I buy an air purifier?
Before you do, know that air purifiers are not a cure-all. There is very little medical evidence to support that air purifiers directly help improve your health or alleviate allergies and respiratory symptoms.
That’s due in part to the fact that it is very difficult to separate the effects of known air-quality pollutants in your home from other environmental and genetic factors. But if you are an allergy or asthma sufferer, an air purifier may be helpful for you as it will be good at removing fine airborne particles.