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Portable Air Cleaner (HEPA filter) buying guide

Choose only air cleaners that have mechanical filtration ( particulate filter media) with MERV 13 or higher or HEPA designation. Watch out for ionizers that can produce hazardous ozone. How to choose? There is help!


1) Air Quality Expert (ASHRAE Epidemic Task Force) Marwa Zaatari and

2)Environmental engineering professor, Dr Shelly Miller offers a report and air cleaner selection guide

3) has an excellent air filter recommendation tool

4) California Air Resources Board

5) Association of Home Appliance Manufacturers

6) ASHRAE: The American Society of Heating, Refrigerating and Air-Conditioning Engineers

7) DIY box fan filters (Corsi-Rosenthal boxes)

We know that air filters work to remove airborne virus particles.

Choose only air cleaners that have mechanical filtration ( particulate filter media) with MERV 13 or higher or HEPA designation.

Be aware of false marketing:

99% HEPA
HEPA Ultra
Ionic HEPA
HEPA Efficiency
HEPA Functions
HEPA Action
Plasma HEPA
Super HEPA

are ALL subpar versions of what constitutes a HEPA air filter.

Stay away of fancy technology marketing:

Plasma wave
Fragrance Sponge
UV Light Sanitizer Eliminates
NCCO technology
Active oxygen generator
ionic purifier + composite catalyst
cold catalyst layer
negative ion generator
Cold Plasma
Hydroxyl Generators

note: Ionization produces ozone, which is hazardous to health

Open Letter to address the use of Electronic Air Cleaning Equipment in Buildings

by Dr. Marwa Zaatari, Dr. Marcel Harmon
Reviewed and supported by: Dr. Linsey Marr, Dr. Jose Luis Jimenez, Dr. William Bahnfleth, Dr. Shelly Miller, Dr. Jeff Siegel, Mr. Hoy Bohanon, Dr. Elliott Gall, Dr. Kim Prather, Dr. Delphine Farmer, Dr. Brent Stephens, Dr. Richard Corsi, Dr. Wayne Thomann.

Unintended Consequences of Air Cleaning Chemistry
Douglas B. Collins and Delphine K. Farmer

Graph of Air cleaners

  • Start by the area of the room to be cleaned (y axis)
  • Consider cost (x axis)
  • and noise (look at color of the dot; <55 db at highest setting is probably a good level) colors = noise level expressed in db (decibel)
Portable Air Cleaners comparison graph, HEPA, MERV13, CADR, cost, db decibels noise
Marwa Zaatari’s graph comparing Portable Air Cleaners based on CADR, cost, and noise level decibels

*note: CADR stands for Clean Air Delivery Rate

January 18, 2021 original post / thread
April 3, 2021 update
June 1, 2021 update
Aug 22, 2021 update with Corsi-Rosenthal box fan filter

Latest Update

Latest graph and much more here!

Sept 18, 2021 update

Dr Shelly Miller – Report and Calculator

Environmental engineering professor, Dr Shelly Miller, offers a report here on air cleaners.

This spreadsheet is the Harvard-CU Boulder Portable Air Cleaner Calculator for Schools – it can help you determine what air cleaner to use based on the size of the room etc.

And this is a 5 minute video about how to use the Air Cleaner Tool

California Air Resources Board

Also, the California Air Resources Board has a big list of devices that they have certified.

Since 2010, all portable indoor air cleaning devices sold to people or businesses in California are required to be certified by CARB. As of October 2020, electronic in-duct air cleaning devices are also subject to the regulation. To be certified, all air cleaners must be tested for electrical safety. Electronic air cleaners must also be tested for ozone emissions and meet an ozone emission concentration limit of 0.050 parts per million (50 ppb). 

Association of Home Appliance Manufacturers

The Association of Home Appliance Manufacturers certifies air cleaners, so the AHAM Verifide seal is a good place to start. More resources here:

ASHRAE guidance

ASHRAE PDF: In room air cleaner guidance for reducing covid-19 in air in your space or room.
When to use an in-room (separate from HVAC) air cleaner, and how to choose the right one.

DIY box fan filters

Also known as a Corsi/Rosenthal box, this DIY method of building your own air filter with MERV13 furnace filters and a box fan are a cost-effective way to help clear indoor air from airborne virus particles!