You know I was thinking about your heater idea and it came to me, why not make it a heater & air purifier! On the intake add a activated carbon pads(they look like green scrub pads but black and usually bigger) and maybe even a paper filter, one for a lawnmower should do not hepa grade but will get the small stuff.

This idea may require some custom fabrication to hold the filters.

Not sure how the fans would handle it. But its an idea. Thought I throw it out there. I ran across this post and now have a one board going myself Hopefully soon get solar implemented once I have all the pieces.