The rapid spread of the Omicron variant of COVID-19 has prompted Allison Bailes of Energy Vanguard to revisit the box fan air cleaner that he built (and wrote about) back in 2020. Assembled from four or five MERV-13 air filters taped together and mounted to a standard 20-inch household box fan, the so-called Comparetto cube provides whole-room air cleaning performance comparable to commercial HEPA air cleaners for minimal cost. In this update, Bailes describes how a simple shroud mounted to the box fan improves its performance.

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