re: Shop Air Filter

With 90+ temperatures, you may want the fan blowing outwards, though since it is collecting warmer air near the ceiling, maybe not.   In the winter having it blow outwards definitely makes it a little chilly out there. 

4" filters will help reduced the airflow drop off.  That helped a lot with mine.  I recommend getting a cheap anemometer to check the air flow and whether it is sucking air in from the front and reducing the amount of air going through the filter.  You can also use it to check whether the flow has dropped enough with dust accumulation that it is time to swap out the filters. 

I have a couple of air quality meters that I use to monitor how well my filter is clearing the particulates from the air.  I actually bought 2 units to give me a sense of whether they are providing accurate results.  Both give similar results.   This unit from Temtop is the one that I leave running full time in the shop.  The M10i model logs history over the web that you can look at through their app.  I recently knocked the M10i on the floor and broke it and I bought the M10+ model but unfortunately, it does not seem to have the logging feature.    The other one is from EG.  I mostly use to it to spot check.  It also shows PM 1.0 and PM 10 levels on top of PM2.5.  Both also measure VOC and formaldehyde levels.  Those levels tend to spike when I use finishes in the shop and is a queue to open my garage door.   You may find other units on Amazon, some which may also have data logging capabilities.