@Want to upgrade my old 4-filter CR box to a simpler 1-filter design, but I no longer have the cardboard box that the fan came in to cut into a plenum. Can anyone share a CR box design that doesn’t require the fan’s box? Please and thank you!! #CRbox
Cam@johncormier You can simply strap or (more ideally) tape the filter to the fan. I believe the plenum improves performance, but I’m not sure by how much. Or build a plenum out of suitably sized cardboard/foam board/plywood etc? @DavidElfstrom may have more suggestions
@thoughtsofawho @DavidElfstrom In the end, that’s exactly what I did. Had forgotten how sturdy the o.g. CR box design was. Anyway, it was quite easy to just tape the filter to the fan, absent the plenum. It’s not pretty, but it has a much smaller footprint than the CR box it replaces. And, of course, if it works that’s what counts! (Not to mention the fact that I only have to buy one expensive filter instead of 4!)
David Elfstrom@johncormier @thoughtsofawho Adding a small plenum made from the box the fan came in helps and makes filter changes easier but it's not essential. Making a shroud on the outlet is the most important performance improvement that is even more important for a 1-filter design than for the 4+ filter design.
@johncormier @thoughtsofawho For the Lasko Air Flex (box fan with filter holder) the CADR would increase substantially with a shroud. I brought this to their attention but they did nothing about it.
@DavidElfstrom @thoughtsofawho awesome, great to read your take! Just to be clear, by shroud I assume you mean the masking that we do (e.g. with tape) to modify the output grille so that it approximates the area swept by the oscillating fan blades?
@johncormier @thoughtsofawho Yes, you can either cut a cardboard one or cover up the face with tape. With a 1-filter design it will be narrower than the swept fan tip diameter. To find it, see where tissue is sucked on to the face. That is what needs blocking with tape.