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Air Purifier Filter Replacement Guide

Air Purifier Replacement Guide


An air purifier eliminates much of the annoying stuff that floats about where you live or work. You may be wondering how it disposes of the waste and how that affects the unit.

Well, all that is trapped in the media of various filters, by stages. As these fill up, they eventually lose much of their cleaning capacity.

Cleaning or replacing the filters can be critical, because once the air coursing through cannot find open passages, the purifier ceases to operate effectively.

Various kinds of replaceable media are used, including HEPA main media and carbon-based pre-filters. These work together to attract and catch particles such as dust, molds, pollens, and microorganism while neutralizing polluting smells and gases in many cases.

Types of Purifiers

The majority of purifiers do not remove every virus or gaseous particle such as radon. Even models with actual HEPA stages are only at their most efficient when filtering 0.3-micron particles, including dust, pollens, molds, dander, and cigarette fumes.

Furnace Filters. One pricey alternative to purifying single rooms is a filter for the furnace. These are not dedicated air cleaners as they just replace the whole-house filter. Nearly all such models are good at eliminating fume and dust particles as well as pollens.

Whole-house filtering media are not the most efficient in general and normally have to be changed at 3 month intervals, since airflow may become restricted otherwise.

Then again, they do not rely on separate power supplies and are less costly to operate than most room models.

Portable Purifiers. A room model can offer a measure of relief from allergies and asthma. If you have pets or smoke, you will need these to remove smells as much as any dander and fumes.
A variety of portable models rely on mechanical filtering media, while others utilize electronics. These designs are the focus of this air purifier filter replacement guide.

Air Purifiers Help You Breathe Easier

Air purifiers employ a range of methods to handle airborne pollution. HEPA designs work by mechanically filtering airborne particles.

As their fans cram in air through sealed housings, these particles are dispersed through filtering media. This technology generally offers the highest cleaning efficiency and does not generate any ozone, unlike rival electronic designs.

The fans can be noisy, although some users prefer the white noise they produce. Not all models that depend on mechanical filtering incorporate actual HEPA media, so you must check for the presence of these in models that you are considering.

A number rely on electronics rather than or along with mechanical filters. An electronic ionizer collects and reverses the charges of aerial particles, which are released right after. These are attracted to the floor, walls, furniture, clothes, effectively displaced from the room air then deposited elsewhere.

In practice, you may still have to use wipes and vacuums to displace many allergens from your surroundings, to make sure these do not return to your rooms.

Certain models use electrostatic precipitators that conveniently collect the charged particles with an electrically polarized metal plate.

Want to know why?

BlueAir Best Air Purifier Replacement Guide

Electronics are efficient at collecting particulates as tiny as 0.1 microns in size. But, these can also generate minute amounts of lung-irritating ozone, although at levels generally below that determined to be safe by UL and the government.

Those designs that induce a minute charge on mechanical sieves for more efficient collection have electrical potentials that are too low for generating appreciable levels of ozone. Most ionizing and electrostatic designs will still generate tiny volumes as byproducts.

That said, dedicated generators are used as industrial air purifying units in hotels and other hospitality venues. These standalone units release large volumes in rooms undergoing maintenance, thus neutralizing irritating chemicals and smells. Although this works in an industrial setting, the method can be risky and is best avoided at home.

Other than industrial ozone-generating units, other electronic or mechanical methods are not that useful against gaseous chemicals or sharp smells. Certain models do perform extra filtering against chemicals, with many typically relying on activated carbons to trap many pollutants. The best have several such filters in place and will cost more in comparison to most consumer models.

Filter And Pre-Filter Types

Many designs depend on HEPA media to trap the smallest pollutants. Each type offers specific advantages over differing operating lifetimes. Filter replacements are normally done in 3-6 month intervals in accordance with usage and version.

HEPA. HEPA denotes High Efficiency Particulate Arrestance. These designs are capable of filtering common pollutants such as dusts, pollens, molds, and other allergens.

HEPA units are certified to eliminate no less than 99.97% of all particles of 0.3-micron diameter and bigger. This is a critical size that is known to have the greatest likelihood of penetration through most filtering media. As these are the hardest to catch and displace, their removal is the basis on which HEPA-based filtering is standardized.

Unclean air is normally drawn in through vents, where visibly bigger flecks are trapped in the kinds of washable pre-filters that are used in most HEPA models. The flow then continues through the main element, which is comprised of millions of slender fiberglass strands that altogether form a structure similar to that of minutely folded paper.

In manufacture, HEPA filtering media is continuously spun then pleated while still warm, preventing cracks and tears from appearing. Air that is circulated throughout these minute fibers will progressively deposit allergens of various diameters on them, including dusts, pollens, dander, and spores.

A number of HEPA units include additional carbon pre-filters for capturing chemicals, gas, and other odorous particles. Once past every filtration step, the purified air is dispersed into the surroundings.

HEGA. HEGA denotes High Efficiency Gas Absorption fibres, a high-performance carbon fabric with military applications that are typically found in Austin Air’s range of air purifiers. These can filter out most pollutants such as dust, smoke, pollens, molds, smog, and odorous gas particles. It is not as long-lasting as conventional activated-carbon filters, though.

Hyper-HEPA. These incorporate advanced HEPA elements with greater capacities and longer life spans than that of regular filters, these are typically used in IQAir’s products. The advanced medium widens the lower filtering range to 0.003 microns, a hundredfold efficiency over that of standard HEPA media.

Activated carbon. This media is based on varieties of oxygen-enriched compounds, such as bituminous and anthracite coals, coconut husks, bamboo, rayon fibers, and even sawgrasses. Adsorption processes work when materials are chemically attracted and bound to the filtering surfaces.

Carbonized material enriched with oxygen exposes millions of interior pores. So numerous are these minute pores, that an entire surface exposed by a single pound can reach around 60-150 acres in total area. The large extent is effective for adsorbing polluting gas and neutralizing airborne chemicals and smoke odors.

Chemical and other gas particles are usually too tiny to be caught by HEPA filtration, but almost all bond promptly to these large carbonized surfaces. The larger these filters, the greater the volume of chemical-laced air that they can treat and for longer periods of time.

Activated-carbon media is capable of adsorbing some 50 to 65% in mass of gaseous and other chemical fumes. At capacity, it will not adsorb further and will need to be changed once full.

Impregnated carbon. This type of filter contains an extra ‘chemisorbing’ compound that removes certain volatile organic compounds (VOC), which are mostly oxidizing agents such as potassium-based permanganates, iodides, and hydroxides.

This addition widens the filtering range, eliminating a range of chemical vapors and other polluting substances. The compound catches and/or oxidizes such particles for decomposition into tinier and more inert components, including water vapor.

How HEPA Works

HEPA filtering is basically simple and inexpensive to implement, making it an affordable option for nearly all homeowners.

As a physical method, it depends on momentum and friction to arrest the miniscule specks. These flow at high speeds across dense mats of netted fibers, between openings of varying width.

The netting is not fine enough to filter everything passing through, but is densely packed to the point of impeding everything but air and industrial gases from passing through.

Dense sheets of tiny fiberglass strands are smoothly pleated then mounted in airtight plastic or metal housings with edges that are thoroughly sealed.

When turned on, fans quickly push air through the filtering surfaces to their opposite sides. The seamless construction ensures that the flows cannot leak elsewhere and bypass the filtration process.

The fiber in a HEPA media acts to filter particulate flows using a trio of methods. These rely on the relatively large variances in diameters between different particulates.

Some of these airborne clouds of particles will feature miniscule dispersed solids, such as smoky fumes, whereas others are composed more of far tinier gas molecules and atoms. These are small enough to course mostly unimpeded past any filtering media.

Coarser particulates may have content that is still too minute to be discernable to human senses. Then again, these contain compound structures that are much bigger in scale than the molecules and atoms of gases, by a factor of hundreds and even thousands.

Such particulate solids may have so much momenta that their contents do not readily flow with the passage of air. Larger flecks are more or less certain to crash or slide among the strands in accordance with their microscopic sizes. Gas is thus drawn quickly through the media with hardly any resistance, even as nearly all non-gaseous particles are trapped.

The biggest particles will have diameters wider than or nearly matching that of the filter’s strands, which are normally around 0.5 microns in size or larger.

These are readily caught via impaction, since they cannot alter their individual courses from sheer momentum and will just bump into strands and eventually stop somewhere.

Particles that are narrower than the average width of the strands but which are otherwise not much smaller are caught via interception.

As these flow around fiber strands, most will eventually pass near enough to slide along their structures, eventually getting caught in time.

The smallest polluting particles are of 0.1-micron size, smaller in diameter than most strands. These are bounced about in the turbulence and further slowed in encounters with atmospheric particles. They drift and eventually rebound into the surrounding fibers, at which point they are eventually caught up.

HEPA Standards

The diffusing process thus progressively captures nearly every particle passing through. However, the 0.3-micron-sized particles that move around at the media’s lower intercept limits while surpassing its diffusion properties are of a size to get through unimpeded.

By specifying denser mediums at the limit of 0.3 microns, a designer can ensure that there will be enough HEPA capacity to catch the majority or some 99.97% of all particles of that size or so, based on US standards.

The EU on the other hand rates HEPA effectiveness along a sliding scale. The lowest E10 rating certifies machines that can trap no less than 85% of all 0.3-micron particles. The best European H13 designs are rated to eliminate 99.95%, which are the ones worth getting.

Usage And Replacement

Owners who accept and understand the operational constraints of consumer purifiers will know better about what to expect. Portable models are normally capable of eliminating airborne allergens.

These devices are not so useful against larger and heavier pollutants, such as dust mite droppings that fly about on occasion and irritate a lot of people.

Costs Of Using Air Purifiers

When tallying up long-run maintenance expenses, the replacement of filter elements must be done according to schedule in order to ensure effective operation.

A number of designs do not need many filter changes if at all. Some feature multiple pre-filters such as carbon and others in addition to the main HEPA cartridge, most of which will have to be changed at varying intervals. Dissimilar models may require different replacement schedules, with expenses varying among types.

With typical HEPA consumer models as examples, filters can cost some 70-200 USD and will need changing every three or five years.

Pre-filters may cost some 20-30 USD and should be changed after at least three months to a year. Activated-carbon elements can cost something like 15-150 USD and will need changing after six months to around a year or two.

Frequency Of Filter Replacements



With most HEPA units, do remember to estimate the cost of periodic replacements. If the model incorporates both carbon pre-filters and HEPA filters or other packaged mixes, the various media will have differing life spans and may have to be swapped independently.

HEPA media can perform well in regular settings for half a year to perhaps five or so. Estimates can vary based on manufacturing quality, the gross area of all the surfaces, and operating conditions.

Less expensive models generally involve annual filter replacements, while premium brands tend to recommend 3-to-5 year replacement schedules for their air purifiers.

When To Replace Filters

Some designs incorporate timers that signal for replacements in fixed intervals, which correspond to recommended schedules. Some offer more exact estimates by factoring in operating time in total as well as average fan speeds.

HEPA Filter Details

Experienced makers will seal in as well as gasket filtering media against flow bypass, for prolonged high-efficiency operation. As 90% of all particles that get trapped are of 0.3-micron size in numbers and not mass, it is vital for HEPA units to meet the minimum criteria.

Real HEPA filter elements come identified as ‘True’ or ‘Medical-grade’ HEPA. Many buyers are confused by similar-sounding terms like ‘HEPA-type’, so do not get taken in by the marketing hype too easily.

We suggest that you stick with air purifiers that feature heavily sealed models enclosing fully-certified HEPA media. Such units are rated in terms of square feet of unfolded surface area.

Manufacturing design and build as much as shipping and handling can affect quality. Each delicate fold should be perfectly pleated, with no sharp edges where cracks can eventually form.

Larger room units can contain up to 80 square feet of media, good ones will provide at least 50 or so. A number of HEPA models feature smaller filtering surfaces, these will need more frequent replacement.

Chemical vapors, gas, finer fumes, and smells, as well as viruses and certain bacteria, may pass straight through even HEPA filters. The best designs tend to include an extra filtering stage in the form of pricey carbon canisters that can handle these VOCs.

Outgassing can arise in the glues and silicone gasket parts used to affix filter media to unit housings. Be aware that sealed units with sufficient ventilation for airflow tend to become noisier at the highest speeds, with some reaching sound levels of as high as 70dB.

Pre-Filter Details

Pre-filters are designed to trap bigger specks such as pollen and hairs prior to HEPA filtration. There are many benefits to using multiple filtering steps, as less efficient elements can be arranged to work in sequence with finer-particle media.

One key benefit of using pre-filters is that these extend the lifespan of pricier HEPA media and VOC cartridges, by stopping them from being clogged and coated with dust. HEPA filtration is best at trapping sub-micron structures and is not too good at catching coarser particles.

Pre-filtration incurs more maintenance though. Elements have to be cleaned and/or replaced at intervals and pre-filter replacement costs can be high for certain models.

Inexpensive polyester-mesh carbon pre-filters can require changing in 2-to-3 month intervals in order to retain their anti-odor properties. With dust and smoke particles or pet dander, these types will require more regular maintenance, perhaps as often as every month.

Premium models typically feature longer-lasting pre-filters. IQAir’s designs feature some of the more advanced pre-filtration stages. Their pre-filters by themselves will trap 0.3 micron-sized particles at 55% efficiency, surpassing that of most consumer purifiers.

The outside surfaces of Austin Air’s pre-filters can be vacuumed with no disassembly, which is a nice convenience. These packages can last many years with constant maintenance.

Pre-Filtration Efficiency

Not many pre-filters can arrest sub-micron particles, although RabbitAir’s Electrostatic versions can trap particles down to 1.0 microns.

Less advanced air purifiers rely on polyester-mesh layers or else polyurethane foams. Many have coatings of activated-carbon charcoals that can catch 15-micron particles and larger.

The carbonized material provides a remedy for the odors in the short run, although it prevents the foam pre-filters form being washed.

A pre-filter that only needs cleaning is preferable to one that requires periodic changing. Brands such as Sharp and RabbitAir employ lint screens that are easily washed, although these are mainly good for trapping 20-micron and coarser particles. Silver nano-coatings are sometimes applied to harden interior surfaces against microbial growths.

Universal pre-filters are simple bands of material that can be trimmed to match the original part. These have become widely available, so it is easier to experiment with mixing and matching various pre-filter materials on a budget.


As air quality brands evolve into a fragmented and reduced market, many models have been dropped and planned product obsolescence has become the rule. The majority of retailers do not stock specialized pre-filters for many models being sold at big-box stores.

Suppliers have started offering generic pre-filter packages while presenting misleading claims at times.

Packaging might indicate a direct replacement for a certain brand’s HEPA filters, even though the item inside the box is actually a carbon-less generic filter.

As a practical example, loads of generic copies of Honeywell’s bestselling 38002 pre-filters can be found online and in stores.

These are usually packed in clear wrapping, whereas genuine parts are shipped in red/white packaging and feature precise templates that will match most housings, a detail which numerous generic brands skip.

Although generic pre-filters can be of good quality, buyers have encountered issues with many of these knock-off items, such as slight chemical or decaying smells.

Carbonized granules that drop off and clog the main filter’s openings, as well as thin and inconsistent media, can also cause problems, so it pays off to use original replacement parts whenever possible.