HEPA Air Purifier Buying Guide
This guide explains HEPA filters, what to look for in a good HEPA air purifier and how to choose one to fit your needs.
A HEPA filter is a High Efficiency Particle Air (HEPA) filter. The “A” is also defined as “absorbing” and “arrestance.” Regardless, it means the filter is really good at removing particles from the air. The filters are composed of a rigid frame and a pleated media constructed from glass fibers (fiberglass) to create a dense, tight mesh.
HEPA Standards: To be certified HEPA, a filter must remove 99.97% of particles from the air that are .3 microns or larger.
A single micron is 39 millionths of an inch, so .3 microns is 118 millionths of an inch.
Those numbers are impressive, but only makes sense in comparison to particle size. Here are some comparisons:
A human hair and pet fur can range from 60 to 80 microns.
- Bacteria are .2 to 3 microns or larger.
- Dust ranges from .5 to 10 microns or larger.
- Pet dander (which is the same substance as most, but not all, dust) is .5 to 10 microns.
- Mold spores are 10 to 30 microns.
- Pollen ranges from 15 to 200 microns.
- Dust mites – 100+ microns
- Smoke – .01 to .2 microns
A HEPA filter is your best defense against most solid particles, but some gases can get through them.
That is why smoke and its odors from cigarettes, cigars, wood fires, forest fires and wildfires is notoriously difficult to fully get rid of.
True HEPA vs HEPA and HEPA-type
The term True HEPA is more than a marketing term.
It is a technical term meaning the filter has indeed met the 99.97% filtration requirement. You can only be sure you’re getting this level of filtering if the unit is a true HEPA air purifier.
HEPA: This term is used by some manufacturers to refer to a “HEPA-type” filter. This means that it is similar to a true HEPA.
But you can also be sure that it does not do as good a job removing small particles. If it did, the company would have it certified and label their appliance as a true HEPA air purifier.
Some so-called air purifiers with the HEPA label instead of true HEPA might better be called a true heap.
HEPA-Type: Holmes, Alen and Febreze are the best-known air purifier brands that use HEPA-type filters. Holmes makes True HEPA models too. The others, at this time, don’t.
These filters don’t have any certification. Most claim to remove 98% to 99% of particles, but they fall short of 99.97% of particles down to .3 microns.
A quick search on Amazon shows that HEPA/HEPA-type air purifiers are almost always lower-rated than those with certified HEPA filters.
If you have allergies to dust, pollen, pets or mold, then using a true HEPA is highly recommended.
What About HEPA H13?
HEPA H13 is a true HEPA filter that is also tested to remove 99.95% of particles larger than .1 micron. They remove more viruses, bacteria and VOC/chemical vapors than standard True HEPA.
The Medify Air ‘Wildfire CA Edition’ MA-112 Medical Grade True HEPA H13 Air Purifier in the Top HEPA Air Purifiers list above is an H13 filter, as the name indicates. If you don’t need a unit that large (rated for 2,500 square feet), the Medify MA-40 is also a True HEPA H13 air purifier, and it is rated for 800 square feet.
Can I wash a HEPA filter?
You shouldn’t. Washing might damage it, and the filter would be too hard to dry. You’d likely end up with a moldy filter that did more harm than good.
Can I vacuum a HEPA filter?
Some can be vacuumed. The RabbitAir BioGS 2.0 Ultra Quiet HEPA Air Purifier (SPA-625A) filters can be vacuumed. The air purifier is in the list above. See the Review for a link to a video about vacuuming the True HEPA filter.
Check with the manufacturer (website, owner’s manual) to see if your brand can be vacuumed to prolong its useful life.
What to Look For in an Air Purifier with True HEPA
Some things are essential. Others are optional, but nice to have. Let’s start with the essentials.
The Value of a Pre-Filter
Most air purifiers have a pre-filter. Most of the time, it is a permanent, washable filter. The advantage is that, while washing is a hassle, it cuts down on cost. You’ll spend more on filters over the life of the air purifier than you will on the unit, if it lasts as long as it should.
The value of a pre-filter is that it catches all those “big” pollutants and debris. Hair, pet fur, clumps of dust and many other household nuisances are much larger than a micron. Think about how quickly they would clog the main filter if they weren’t caught in the pre-filter.
Clean the pre-filter after a week or two when you first turn on the air purifier.
Check it every week or two after than until you get a clear idea of how often it needs to be cleaned.
The Value of Activated Carbon Filters
Gas and chemical vapors contain molecules too small to be trapped by a HEPA filter.
That’s why an activated carbon (aka charcoal) filter or filters are useful.
1. The carbon or charcoal in a pre-filter is extremely porous. In fact, 1 pound of activated carbon has a surface area of about an acre – 43,560 square feet.
2. All those pores trap gas and chemical molecules.
3. The carbon/charcoal is extremely hard, so those molecules cannot penetrate or get through and back into the air you breathe.
4. The air that reaches the carbon filter has been filtered by the HEPA filter in most models. This prevents the carbon pores from being plugged with particles.
Can you wash a carbon filter? Vacuum it?
We don’t recommend washing a carbon filter. But you can try vacuuming it.
Sometimes the carbon filter doubles as the pre-filter or is placed before the True HEPA filter. This isn’t the best design. When this happens, check the filter often, and if dust, pet fur and other large debris has built up on it, vacuum it gently.
Other Common Filter Types
Here’s a brief overview of other methods of removing pollutants from the air. They can enhance a True HEPA filter, but can’t replace it.
Ionization: These units emit negatively charged ions, sometimes called anions, that bond with pollutants in the air. The newly formed particles are heavier, so easier to trap.
Ionizers are of two types – those that create ozone and those that don’t. Ozone irritates breathing passages in high amounts. If you have asthma, stay away from ozone. The appliance you’re reviewing should state if it emits ozone and how much.
Germicidal UV light: Ultraviolet light kills bacteria, viruses and mold spores. These lights are typically housed in the center of the appliance, sometimes inside a round HEPA filter, so you shouldn’t see the light produced.
Other Features to Consider
While not essential, these features can make a True HEPA air purifier more effective and using it more convenient.
Air Quality Sensors: A sensor detects the level of pollutants in the air and adjusts fan speed to meet the air cleaning need. The more pollution, the higher the fan speed.
Auto mode: Sensors almost always work hand-in-hand with Auto (or Automatic) Mode. To have the fan speed automatically adjust to air quality, Auto Mode has to be turned on.
Turbo Mode: Some air purifiers have turbo mode. It’s the highest speed of the fan, but to be “turbo,” it should run much faster than the next highest level. Turbo quickly cleans the air. It is used most often when there is an influx of pollutants, such as pollen coming in through open windows on a spring day or cooking odors.
Turbo Mode is usually quite loud, so you won’t want to be near the unit while it is on. We recommend being in another room or leaving the house for an hour or two while it runs.
Timer: A timer allows you to run the unit while you’re away or asleep and have it turn off. It’s an energy saver.
Sizing your HEPA Air Purifier
The product page or box of the air purifier you’re considering should give the square footage rating.
If you have severe allergies and/or pets, we recommend using an air purifier rated for a larger space than you need.
For example, lets say you’re shopping for an air purifier for a 200 square foot bedroom.
- No allergies and no pets: Buy a unit rated for 200 square feet.
- Allergies such as dust, pollen or mold, but no pets: Buy a unit rated for 300-350 square feet.
- You have a furry pet or two, but no allergies: Ditto. A unit rated for 300-350 square feet will serve the purpose.
- You have allergies and pets: Buy a unit rated for 400+ square feet.
The larger the unit, the more times it will clean the air in a room each hour.
A unit rated for 400 square feet will:
- Clean 400 square feet 1X per hour
- Clean 200 square feet 2Xs per hour
- Clean 100 square feet 4X per hour
If you have allergies and/or pets, it makes sense to clean the air more often for more thorough purification.
Similar adjustments should be made if the air in your home is more polluted than normal or if smoke is an issue.
Getting the Most from a HEPA Air Purifier
These tips are taken from our Air Purifier for Dust Buying Guide
- Choose hard flooring, since carpet harbors dust that is stirred up when walked on or vacuumed with a non-HEPA vac.
- Dust from the top down, and then vacuum or damp-mop the flooring.
- Unclutter your home, since clutter gives dust so many places to settle.
- Vacuum with a machine with a True HEPA filter.
- Use a vacuum with bags rather than a bagless model.
- If you use a bagless vacuum, always empty the bin outside.
- Keep dogs bathed and groomed, (and choose a short-hair breed).
- Use air conditioning rather than fans, since fans will pull dust into your home.
- Have a no-shoes policy in the house.
- Use a high-MERV filter in your furnace. MERV is “minimum efficiency reporting value” is a measure of the filter’s effectiveness in trapping particles. The higher the MERV, the better. But be sure your furnace can take a high-MERV filter. Check with your HVAC technician.
What are the Best HEPA Air Purifiers?
- Pure Enrichment PureZone 3-in-1 True HEPA Air Purifier
- Renpho Air Purifier for Home Large Room with True HEPA Filter
- RabbitAir BioGS 2.0 Ultra Quiet True HEPA Air Purifier (SPA-625A)
- Inofia Air Purifier with True HEPA Air Filter
- Elechomes Air Purifiers for Home with True HEPA Filter
- Medify Air ‘Wildfire CA Edition’ MA-112 Medical Grade True HEPA H13 Air Purifier
Each of these models is reviewed above with links to more information and current price with the option to purchase the unit.