Thread by @DavidElfstrom

#corsirosenthalbox flow tests for Lasko 3733 and 3M Filtrete 1900 20x20x1 filters.
Shroud optimization: 20 cm radius (15.75" diameter) /1

Effect of shroud size on outlet flow. Having a shroud is important, but don't stress over it. Without it, air flows backwards at the corners instead of through the filters. /2

The supply voltage makes a difference! Fan speed changes linearly with voltage. Here's the flow range for the accepted 110-125V variation of the nominal 120 V North American distribution supply: /3

Like with flow, the variation in voltage supply directly affects the fan power consumption in watts. /4

But here's what we really want to know: How can we compare a homemade air cleaner made with quality furnace filters to a commercial HEPA air cleaner? Here's the estimated comparable ratings for this Lasko 3733 with 3M Filtrete 1900:
252 CADR, room size 390 square feet. /5

With these estimations in mind, variations of these air cleaners can be tested for performance in accordance with AHAM AC-1-2020 standard. NOTE that in more recent versions it specifies tests at 115 V. Earlier versions specified 120 V. /6

So if we were to do an independent comparison today, we would be testing at 115 V even though supply voltage to homes is 120 V or higher in practice. Here's the estimations at 115 V: /7

Smoke CADR is intended for removing cigarette smoke. What about for viruses? Can we use a larger target particle size? Thread asking for discussion: /8

Back to the shroud, I tested it without one at all, and the flow is lower than if there's the optimal size shroud running on speed 2 instead of speed 3. So adding a shroud is like getting an extra speed setting! /9

This is a 23% improvement over no shroud. When I did it before, I got 36% improvement. Why? The greater the resistance on the inlet, the more likely air will be drawn in at the front near the tips. Earlier test was done with only one filter.