I built my shop in 2012 and have been continuing to refine it since. Because of my location I built the shop to be extraordinarily well insulated and air tight. The upside is it costs me virtually nothing to heat in a cold climate and is comfortable year round. The downside of being so air tight is that there is very little air exchange so any dust I generate stays in the shop (at least for 8-9 months per year).

My power tools are not terribly sophisticated and I don’t have good dust collection. The result of a very tight shop and crappy power tools and lousy dust collection is that in the last three winters I’ve suffered from persistent bronchitis - a condition I’ve never experienced before. So, in addition to going on a quest for better dust collection at the tools I embarked on a quest to increase the efficiency of ambient air filtration.

I’ve had a couple of Jet ambient air filters (AFS 400 and AFS 1000) for quite awhile and they’ve been helpful. But, obviously I needed to do something more to reduce the persistence of fine dust in the shop air.

I looked everywhere for sub-micron filters that could replace the finer secondary filters in both my Jet ambient air filters. I could find nothing that would do much better than the 1 micron Jet replacement filters. Given my struggles with bronchitis I concluded that I needed much finer filtration than that. I stumbled across a video by Stumpy Nubs in which he replaced his Jet AFS 1000 secondary filter with a sub-micron Wynn Environmental filter designed for a cyclone dust collector. Stumpy’s version was clever and located the filter well below the AFS 1000 connected by a flexible duct.

I don’t have the floor space to allow remotely locating the filter like Stumpy and I didn’t want to have to run any ducting because I felt it would reduce the efficiency of the systems. In looking for dust collectors I noticed the Oneida systems that transitioned from a rectangular plenum exiting their dust collectors to a cylindrical HEPA filter. So, I decided I could build a plenum that would make a short transition from my Jet AFS filtration equipment to very fine filters intended for cyclone dust collectors.

I ordered a couple of filters - one from Oneida intended for the Mini-Gorilla cyclone system that provided 40 sq feet of HEPA filtration and another from Wynn Environmental that provided 230 sq ft of (the 13”x34.5” MERV 15 nanofilter). I built a plenum to attach the Oneida filter to my Jet AFS 400 and one to attach the Wynn filter to my AFS 1000. The Oneida filter has a fixture at the bottom allowing for attachment of a standard 2.5” shop vac hose to help in cleaning the filter when it needs it. That seemed like a good idea so I built a bottom for the Wynn filter that allows for attachment of a shop vac hose that is covered with removable Lexan so I can monitor when the filter might benefit from cleaning. This lets me use compressed air to blow dust free from the inside of the filters while vacuuming from the bottom it to increase cleaning efficiency.

I hung both filters facing each other high on opposite walls of the shop with the idea that doing so would be beneficial to air flow. This has proven of no consequence since air flow from the filters is diffused in a large cylindrical pattern and does not create the kind of directional flow that resulted from the original AFS filters. In doing so I considered the advice that mounting the filters high would just pull fine dust up past my face and create problems. But, in my shop there was just really no other place to put them. Also I had previously bought a Powermatic PM 1250 air filter and mounted it inches off the floor under a table on casters that I can position near my work to pull dust I generate from hand tools at the bench, sanding, etc.

The result will, I think, be much cleaner air. The combined Jet AFS 400 and 1000 can filter the air in my small shop up to 25 times per hour to about MERV 15-16. The Powermatic increases that filtering capacity by about 25-30% but does not filter the very fine dust as well. The photos show some the plenums under construction and the plenums and filters mounted as well as a shot of the bottom of the Wynn filter with removable Lexan piece allowing monitoring of the condition of the filter and, when removed, vacuuming of the filter during cleaning.
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