Danny, interesting thought. My first thought was that the filter fibers become electrostatically charged from the air flow. Any thoughts or references to read on how much adding the negative ions adds over the expected charge of the fibers from the airflow?

You’d have to explain why too big of a fan would be ineffective. I’ve built dozens of systems for filtering smell. The more times your air turns over the faster it clears the air. Though I will admit getting it all on the first pass isn’t a significant issue in this case since the rooms air will be filtered a dozen times an hour in some cases.

In this application, you certainly aren’t sucking droplets of spit through the filter and with a appropriate filter even bacteria and germs will not go through the filter. The size of the holes in the filter material don’t change just because you run the air faster through it. If a mask stops the virus in any meaningful way, this will do the same.

One final thing, these fans are not great. You can buy an inline duct fan for $20-60 on amazon that are much stronger and quiter. I am personally building one using 4 20×30 filters and a $100 carbon filter/duct fan combo. These are made to run 24/7 long term. The carbon filter, when inside the ac filters should last for years since the air will already be clean when it hits it.

1. I was wondering about the question Jim Baerg posed about the efficacy of the fan in a horizontal position. Thoughts?

2. Intrigued by your recommendation about Paul Bronks’ Twitter posts (@SlenderSherbet), I checked out his page and found, alas, that his account had been cancelled. Nuts.

Kathleen, yes, this DIY portable air cleaner is great for smoke and many people are using them for that, too. High-MERV filters remove lots of particulates from the air. It doesn’t matter whether they’re virus-carrying aerosols or tiny bits of ash from fires.

Jim, you can’t simply put an Alnor flow hood on the fan to measure its air flow rate. As with the Heisenberg Principle for subatomic particles, the measurement interferes with what you’re trying to measure. You need a different setup. See this Twitter thread from John Semmelhack to find out what they did. With no filters, they measured 1,025 cfm on low speed with a Lasko fan. They 575 cfm on low speed for the Comparetto Cube.