1. Simple mechanical air cleaning (using physical filtration without ionizers, UV light, etc.), ideally because the unit has no potentially-harmful electronic cleaning features and not simply because those can be disabled
  2. Maximize Clean Air Delivery Rate (CADR) at ≤45 dBA sound pressure (noise level @ ~1 meter) so as to avoid provoking the filter getting turned off
  3. “Schedulable” and/or compatible with a plug-based timer or motion sensor to maximize filter life and minimize power usage and burden on people (ideally, it resumes its previous settings after power loss)
  4. Clean air discharging “upwards” to breathing height rather than side discharge (per Harvard Healthy Buildings study and ASHRAE 241), especially if a “45-degree” angle from vertical is used to promote better room mixing
  5. Suitability for a 900 sq ft (8500 cu ft) classroom, such as size, sturdiness, filter guards, fan blade finger protection, stability (against tipping over), and ability to impede turning down the fan speed
  6. A vacuumable or washable pre-filter can extend the life of the HEPA or high-MERV filter and is therefore a positive, especially if it can be accessed easily and quickly; activated carbon filters help with odors and VOCs (at the expense of CADR), but as they do not remove particulate matter or viruses, they are considered optional
  7. Confidence in the manufacturer, biasing toward those most likely to continue producing replacement filters (or for which reputable HVAC-standard or third-party options are available), and those offering longer and more comprehensive warranties that aren’t invalidated by classroom use

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Back to the Safe Indoor Air Resources homepage at safeindoorair.org.

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