An air filter is a sieve that catches airborne particles, human and pet hair, volatile chemicals, and odors, removing them from the air. But many filterless air purifiers filter less! A central vacuum cleaner system just blows the dirt outside, but air purifiers without filters must do something with the impurities removed from the air.

The air purification market is filled with shameless hucksters pushing "free" goods or using arcane terminology to obscure the dangers or costs of their products. It's well known that one major air cleaner marketing scam is selling the filtered air purifier cheap as a loss leader for high priced replacement filters. But just as frequent is the "costless" siren song about never having to buy replacement filters.

The notion of an effortless air purifier sure appeals to me. That's why I like automatic operation and air filter replacement intervals up to 5 years. While that is close to the lowest possible user exertion, and is very low maintenance, it is not filterless.

Electrostatic

The majority of air cleaners sold as not requiring replacement air filter media are electronic: electrostatic precipitators. This includes market leaders Ionic Breeze, Oreck, and Friedrich C90, as well as a host of filterless air purifier wannabees. These air cleaners electrically charge airborne impurities and then gather them on an oppositely charged collectors or grids. Where does the accumulated mess go? Inside the air purifier! Most of it builds up on the metal collection plates or grids.

These collectors must be cleaned very frequently, or they begin to let dirty air slip past. As time passes, especially where there is cigarette smoking or grease frying, the collector plates build up an oxidized film layer.

This film layer can be very difficult to remove. When this insulation builds up, electrostatic forces of attraction diminish, leading to bypassing, sparking, and lowered capture rates. Particles may also stick to the inner parts and surfaces of the machine, pouring out when it is turned on. So many so-called filterless air purifiers end up being the filter.

Once the colector plate is oxidized, wires and connectors damaged, or surfaces poorly mated causing arching and ozone, you get to buy a new collector plate. These are costly.

So the electrostatic models are not really filterless. Electrostatic "filterless" air cleaning devices may actually have filters, or have problems, costs, and limitations not mentioned in advertising.

Ionizers

While many filtered air purifiers are marketed as "ionic", true ionizers simply emit ions into the air. These cause airborne particles to clump together, growing until they become heavy enough to fall to the floor or stick to walls, draperies, and furniture.

While simple ionizer air purifiers are filterless, the dirt is not gone. It will become airborne again when weather changes or drafts stir. Ionizers gather only particles, so unless they have high ozone emissions there is no chemical/odor removal.

Ionizers using both polarities, positive and negative, to charge airborne impurities, can create an oxidation environment which surrounds water molecules in the air, destroying particles and inactivating microorganisms. Called "plasmaclusters", this is typically incorporated as an add on to HEPA filtered machines.

Photocatalytic Oxidation: "PCO"

The air purifying technology which has the best chance of producing a truely filterless air purifier is photocatalytic oxidation (PCO).

No filters are required for PCO systems, which may be as simple as a single painted florescent light bulb. Ultraviolet rays excite metal semiconductors, which produce oxidants capable of destroying smaller particulates, chemicals, and odors.

Since the tiniest particles are the deadliest and most difficult to filter conventionally, PCO is a technological breakthrough.

Pollutants, both chemicals and particles, are not captured, they are vaporized, gone, changed into carbon dioxide and water. While PCO can actually be filterless, filters are usually used to capture larger particles, to big to burn up.

Photocat systems still require annual replacement of the ultraviolet lamp, so are not zero maintenance.

A couple examples of PCO purifiers are the Nanobreeze and Pionair

HEPA filtered air purifier technology is the standard by which emerging filterless air purifier concepts are evaluated. No perfect filter free air cleaner has been developed, most have risks or defects. I encourage everyone to try the PCO and Plasmacluster technologies, and not to be fooled by pie in the sky marketing.