Frequently Asked Questions

It is a suitable replacement for portable HEPA filters?

As long a good seal can be made between the filter and the fan, the filters achieve their manufacturers’ specified performance, so a MERV13 filter used in a box fan filter can achieve MERV13 performance.  While HEPA filters have higher particle filtration efficiency, box fan filters achieve a higher air flow that more than compensates for the lower filtration efficiency (clean air delivery rate = flow x filtration efficiency).

Is there more science I can read?

The strongest motivation for adding air purifiers to indoor spaces comes from the scientific literature demonstrating the airborne transmission route for COVID, which is summarized on this CDC page and this very recent review article.

Here’s one very recent study (not yet peer-reviewed) that showed adding air filtration to a classroom with masked students can reduce the concentration of viral particles in the room by 30x–compared with 8x for masks alone–relative to a room with no mitigation strategies.

Isn’t this just blowing COVID particles on everybody?

For the smaller airborne particles that will enter these filters, they already have the ability to travel around the room and build up in concentration if not removed or diluted with fresh air.  Because these filters collect 65-90% of the particles that enter them, depending on the size, the air coming out of these filters is the cleanest in the room.

Where should I put it?

The best place to put it is typically as close to the center of the room as is practical, and approximately at head height.  But putting it anywhere will help, just try to avoid placing it right against a wall, or near an open window, which is already providing fresh air.

Is this a replacement for masks?

No, room air filtration is one of many layers of protection–including masks, distance, improved ventilation with outside air, and vaccination–that should all be used simultaneously to minimize risk.

How loud is it?

We measured 52 dBa on medium speed with a Lasko fan.  It’s basically as loud as the fan by itself, but a little quieter because the filter reduces the air flow through the fan, which reduces noise, just as turning the fan speed down would. We have kits deployed in classrooms and the teachers say there is no disturbance at medium setting. Many teachers turn it up to high between classes or while out of the room.

What else can I do?

Adding air filtration is just one way to mitigate airborne transmission of COVID.  We hope that schools are already opening windows and doors when possible and upgrading central HVAC to provide more air flow and better filtration. But when open windows aren’t an option or building-wide upgrades would take too long to meet the current urgent need, portable air purifiers can help right away.