Evidence · airborne illness

Are CR boxes effective against COVID?

CR boxes rose to fame as a pandemic tool. What does the evidence actually support in 2025?

Our recommendation
CleanAirKits Luggable XL Ultra (7-Fan)

681 m³/h CADR, MERV-13, under 35 dB — powerful whole-home clean air — no proprietary lock-in, ships from the UK.

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What they do

Airborne respiratory particles travel on aerosols in the size range MERV-13 captures. Running a box raises a room's filtered air-change rate, lowering the concentration of those particles — which reduces exposure.

What they don't do

They don't eliminate close-range transmission, and they don't replace ventilation, vaccination or staying home when ill. Filtration is one effective layer.

Bottom line

A well-built, well-sized box meaningfully reduces airborne particle concentration in a shared room — a cheap, sensible layer, especially in classrooms. Fuller evidence: research & efficacy.

Related guides

guide
Research & efficacy

The deeper look.

guide
Research overview

Evidence base.

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Schools

Shared-space clean air.

Frequently asked questions

Do Corsi-Rosenthal boxes help against COVID?

They lower the concentration of airborne respiratory particles by raising a room's filtered air-change rate, reducing exposure — one effective layer, not a complete solution.

Do they replace masks or ventilation?

No — they reduce airborne particle concentration but don't eliminate close-range transmission or replace ventilation, vaccination or isolation when ill.

Where are they most useful?

In shared indoor spaces like classrooms and offices, where raising the filtered air-change rate cuts airborne particle build-up cheaply.