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IQ Air Purifier

How Do Air Purifiers Work? CADR Explained

Running an air purifier is really an excellent way to improve indoor air quality.

These devices utilize internal fans to suck air and send it through a set of filters, which collect an assortment of pollutants before circulating the air back into your living area.

In theory, the air-filtering procedure in the best air purifiers eliminates particles you do not wish to breathe, leaving you with a better, cleaner atmosphere. But how can these devices work -- and what they do?

Fans pull air in

Air purifiers include fans that pull in air and then push it back out in the surroundings. In between, the air passes through filters (generally at least two) that capture pollutant scraps such as dust, pollen, and pet dander.

Air purifiers for pets allow you to pick different fan speeds, which can change how quickly your machine works and how much sound it makes.

You can get noise-level ranges (in decibels) for different fan settings mentioned in your machine's specs. Some air purifiers are much louder than others, but most of the reviewed devices cause minimal disruption, particularly at lower speeds.

Filters take particles out

Most air purifiers utilize mechanical air filters, which trap particles in the filter's material as the fan draws air. The air purifiers we recommend have two kinds of filters: a HEPA filter and a prefilter.


Prefilters grab human hair, fur, and large particles before making it into the most main filter of the purifier.

Most are prefilters disposable, although some are washable. Keep your eye on your prefilter, clean it, or alter it out on the manufacturer's recommended timeline.

True HEPA filter

Coway AP 1512HH

The stuff that makes it beyond a prefilter then moves through the primary filter. HEPA filter is the golden standard for air purifiers.

True HEPA filters eliminate 99.97% of scraps that are 0.3 microns in size or larger.

HEPA filters are made from layers of fiberglass threads. When an air purifier's fan pulls air through the filter, the bigger particles crash into the fibers. The medium-size particles stick to the fibers. The tiniest particles zigzag along the fibers until they get captured.

Yet, "true HEPA" or individual " HEPA" filters are not certified or tested, and if the housing encompassing the filter is not airtight, particles can move through without getting trapped.

Several devices utilize "HEPA-type" filters, which might not perform, in addition to true HEPA. Your best deal is to go for a well-made device that states it uses "true HEPA" or HEPA (i.e., not just"HEPA-type") filters.

Our top selection for air purifiers, the Coway AP-1512HH Mighty, incorporates a HEPA filter with a washable prefilter. It has also got an optional ionizing function that provides particles an electrostatic charge so that they cling to the filter. However, you can turn off if you're concerned about creating ozone, which can be a health issue.

Most of the other models we recommend use HEPA filters.

The exceptions would be the Blueair Blue Pure 211+ and the Blueair Blue Pure 411, which utilizes proprietary HEPASilent filters, and the IQAir HealthPro Plus, which utilizes an exclusive HyperHEPA filter. Both kinds of filters cost up to $200 to replace, more than most conventional HEPA filters.

The HEPASilent filters include loose filters with an ionizer that makes up the difference to catch smaller particles. Since the looser filter allows air to pass through more quickly than a tighter HEPA filter, Blueair's air purifiers have great CADR ratings.

Laboratory evaluations have found that the Blue Pure 211+ is very powerful at cleaning the air.

IQAir claims that its HyperHEPA filters may extract particles as small as 0.003 microns, dangerously little particles, "once inhaled, move straight through the lung tissue and directly into the blood... even the brain!

Scary situations aside, a HyperHEPA filter is not always better than a true HEPA filter in grabbing particles much smaller than 0.3 microns. 

Due to the numerous mechanisms they use to trap particles, HEPA filters would be most efficient at filtering particles smaller than 0.1 microns and larger than 0.4 microns. 

The 0.3-micron size is where they're weakest, and which generates the most variation in efficacy among filters, which explains why the HEPA standard is calibrated to that dimension.

Carbon filter

PureZone true HEPA

Many air purifiers have an extra filter to remove odors and gases. These are made of activated carbon, which may absorb pollutants that pass through it.

However, these filters usually work for only a limited number of gases, so you can't depend on them to remove any odor and gaseous pollutants in your home.

Among the air purifiers we support, several unite carbon filters using their HEPA filters: the Austin Air HealthMate HM400, Pure Enrichment PureZone 3-in-1 True HEPA Air Purifier, Blueair Blue Pure 211+, Blueair Blue Pure 411, and Coway Airmega 400, Levoit LV-H132.


A few air purifiers use electrostatic attraction rather than automatic filtering. When air passes through those devices, particles are charged and drawn to a collection surface or other ions with the opposite charge, with the ion pairs then descending on the floor, wall, or furniture.

As per the Environmental Protection Agency (EPA), there's absolutely no standard for electronic air cleaners. Also, these devices may generate ozone, which is a lung irritant.

The EPA does not suggest air purifiers that produce ozone. For ozone to even succeed in removing indoor air pollutants, it's to exceed levels that are safe for public health.

As mentioned above, the Coway AP-1512HH mighty comes with an ionizer function that switches off. By comparison, ionizing is vital to the purpose of the HEPASilent filters used by Blue Pure 411 and the Blueair Blue Pure 211 +, which means you may not need to turn it off. Blueair says its blockers create very little ozone.

UV light

Some air purifiers have ultraviolet lamps that the producers say destroy dust-mite allergens, germs such as mold and bacteria, and gas pollutants as they pass through the system.

While this seems like a valuable feature, these particles have to be subjected to higher UV light levels for longer than in a typical purifier for the radiation to have any meaningful effect.

The EPA cautions against depending on UV light without also using a HEPA filter, as dead or deactivated particles can still be bothersome. Additionally, air purifiers that rely on ionizing functions, those that use UV lamps can create ozone.

The bottom Line: Air purifiers that attempt to sell you on UV irradiation seemingly aren't the best you can purchase. We suggest the PureZone 3-in-1 True HEPA Air Purifier utilizes a UV light, but it also receives great reviews from users for its design, small size, and low noise.

CADR ratings

When choosing an air purifier, you will want to look at the clean air delivery rate (CADR) of the device, which tells you how successful it is at filtering a particular room size. The Association of Home Appliance Manufacturers assigns the CADR ratings. They usually contain three numbers: one for smoke (the tiniest particle), one for dust, and one for pollen (the biggest particle).

A higher CADR number implies the purifier can filter out more contaminants and clean larger rooms.

By way of instance, a purifier with a CADR of 161, like the Blueair Blue Pure 411, will be sufficient for a small bedroom with low ceilings, but you'd want something like the Coway AirMega 400 with its CADR of 350 to deal with the air in a large living room with high ceilings.

What Air Purifiers Do Not Do

best air purifier for weed smoke

Air purifiers capture just airborne particles, meaning that the devices can't filter the dust, pollen, and dander, which collects on countertops or corners. Purifiers are not an option for deep cleaning your house.

Most air purifiers can't effectively filter out volatile organic compounds (VOCs), either. These are the gases found in dyes, paints, detergents, and other household products; they also create the "new car smell." One air purifier we suggest, the Austin Air Healthmate HM-400, does filter out VOCs.

Odor removal also varies by device. Air purifiers, as an instance, without an activated-carbon filter, might be able to clean physical smoke particles but not the odor and gas from, for example, tobacco smoke. But the majority of the purifiers we advocate do have carbon filters.

Finally, no matter which kinds of filters your air purifier uses, it is essential to replace them regularly. Most filters provide advised replacement timelines depending on how frequently you run your device. If your filter is full of dirt or has reached its capacity, your purifier won't perform well.

About the Author Tom Hanson

I’ve worked as an HVAC tech in Phoenix, AZ for the past 10 years. I created to help home owners select the right portable air conditioner, cooler or air purifier for their needs & budget in just a few minutes.

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