Old habits are hard to break. :-)
With the preponderance of virus and allergen species (and Carbon Monoxide) etc.,
out to do us in, I think using a counterflow air-to-air heat exchanger to raise the air temperature
to 750 degrees F in a chamber either electrically or hydrogen combustion heated would do in
any virus or allergen etc., that can get through a HEPA filter.
For instance inlet air at 300 CFM 14.7 PSIA 65 F raised to 750 F without counterflow
would require 0.25*21.43*685 = 3,670 BTU per minute or 64.5 Kilowatts.
OTOH, counterflow heat exchange with a 20 degree F exit temperature:
0.25*21.43*20 = 107 BTU per minute or 1.88 Kilowatts.
The exhaust of a vacuum cleaner would be a good place to start.
Fred
