Air Purifiers Buyer’s Guide
A bedroom’s air quality is important for getting a good night’s sleep. Many people rely on air purifiers to rid their sleeping quarters of dust mites, microbes and other airborne particles, as well as bacteria, viruses, volatile organic compounds (VOCs), and unpleasant odors. Air purifiers are particularly beneficial to people with allergies and/or asthma. Air purifiers sold today fall into four general categories based on the type of filtration used: HEPA, activated carbon, ionizer, and ozone; some purifier models utilize more than one of these systems, as well as UV technology. Although high-end air purifiers can cost hundreds of dollars, shoppers can usually find models for $100 or less.
This guide will explore the purpose and functionality of air purifiers, some benefits and disadvantages of using one, tips for first-time buyers, and our picks for the top-rated air purifiers according to actual owners.
How Do Air Purifiers Work?
Air purifiers remove contaminants and irritants from indoor air using one of two general techniques:
- Active purification, which uses a process known as ionization to remove contaminants by either completely destroying them or by collecting them on a plate. This makes it somewhat inefficient compared to passive purification.
- Passive purification, which removes pollutants from the air using a filtration system. This is considered the more efficient system since contaminants are removed from the air, rather than converted.
Most air purifiers sold today utilize one (or more) of the following four technologies:
HEPA: An acronym for High Efficiency Particulate Air, HEPA is a filtration system that must (according to industry standards) trap at least 99.7% of particles larger than 0.3 microns, which include chemicals, spores, and other particles that cannot be seen with the human eye.
HEPA filters are accordion-shaped and made of ultrafine fibers. They use four processes to trap particles of different sizes:
- The first process is sieving. As large particles are carried by the airstream, they become trapped in between the filter fibers because they are too large to pass through.
- The second process is interception. Large particles are trapped immediately, and smaller particles that come within a certain distance of a filter fiber will be sucked in and held in place like an adhesive due to chemical or electrostatic attraction.
- The third process is impaction, during which friction causes smaller particles to attach themselves either to the filter fibers or to larger particles that are already stuck to the filter.
- The fourth process is diffusion, which essentially slows down smaller particles, buffeting them with gas particles and increasing the chances of impaction or interception.
Particles accumulate on the filter whenever air passes through, resulting in cleaner air each time. Larger particles are immediately trapped, while smaller ones are trapped later in the process. HEPA filters generally need to be replaced every two to four years; replacement filters are widely available.
HEPA filters are considered the most effective air purifiers for removing particles, as well as the most common and, in most cases, the cheapest. However, they do not remove odors or volatile organic compounds (VOCs), which are emitted from paint, adhesives, and other gas pollutants. One important note: some purifiers advertise as using ‘HEPA-like technology’ or use similar verbiage, but this usually means the filters do not meet official HEPA standards.
Activated carbon: ‘Activated carbon’ (also known as activated charcoal) refers to a form of carbon that has been modified with small, porous openings that expand its surface area. Active carbon technology employs filters that feature low-volume pores that are extremely absorbent and react chemically with some pollutants, sticking to them firmly.
As a result, activated carbon purifiers trap odors, VOCs, and other emissions that cannot be trapped by HEPA filters. However, they are less efficient when it comes to trapping dust mites, microbes, and other pollutants. For this reason, some purifiers feature HEPA and activated carbon filters.
Ionizer: Also known as negative ion purifiers, ionizers rely on active purification (unlike HEPA and activated carbon purifiers that use the passive method). Ionizers essentially zap particles with a chemical charge and collect them using one of two methods:
- The particles are drawn to the purifier, where they can be wiped off.
- The particles collide with other particles, which causes them to stick to the other particles and eventually become unable to float; they may then be swept up or vacuumed.
This method, while scientifically advanced, is somewhat inefficient because it transfers particles to other areas of the room, rather than absorbing them or trapping them in a filter. This poses the risk of the particles breaking free and reentering the air.
Ozone: Ozone purifiers clean the air using ozone gas. This technology is controversial because ozone, when produced at high levels, can be toxic to humans. Long-term exposure to smaller amounts can also lead to health problems. As a result, ozone purifiers have not received official approval from any federal safety oversight agency.
The upside to ozone purifiers is that they are effective at removing odors and some gases — but not dust or other particles. They can also be used to sterilize bacteria and molds — but only in well-ventilated environments. As a result, ozone purifiers often feature ionizers as well.
UV technology: UV technology uses active purification to sterilize mold, bacteria, and viruses, which prevents them from being able to reproduce. However, this technology is not particularly effective at targeting allergens.
The table below summarizes the key differences between HEPA, active carbon, ionizer, ozone, and UV purification technology:
Regardless of the technology used, air purifiers commonly feature the following components:
- A timer that can be programmed for certain intervals.
- Adjustable speeds, which include lower settings for quieter purification and higher settings for more effective purification.
- Manual or remote controls. Most purifiers sold today feature the former.
The following components are associated with certain purification technologies:
- HEPA and activated carbon purifiers feature a filter, which may need to be changed every six months to two years, depending on the model; some models feature washable filters, but these are considered less effective. These purifiers also have an indicator light that lets owners know when the filter needs to be replaced.
- HEPA and activated carbon purifiers use a fan to draw in particles, bacteria, and other contaminants, where they become stuck to the filter.
- More advanced HEPA and activated carbon purifiers are equipped with contaminant sensors that automatically adjust the settings based on how dirty or clean the room is.
- Active purifiers feature an ionizer (see above), which hits contaminants with a chemical charge and either removes (but does not eliminate) them from the air or converts them into harmless molecules.
Purifiers are considered a sleep aid because airborne contaminants can cause health problems like congestion, headaches, stuffy noses, sneezing, and shortness of breath — all of which are proven to negatively affect sleep quality. This is especially true with people who have allergies, as well as those with asthma.
Additionally, most purifiers produce a subtle whirring sound that similar to the output of white noise machines, which are also used as sleep aids. White noise and other noise colors (such as pink) drown outside noise and allow people to fall asleep more easily. Some air purifiers come with a specialized ‘sleep’ setting, which is usually the lowest and quietest, and thus the most conducive to sleep.