This week we fired up the “OMG the kids have COVID” air treatment system from April: MERV 13 furnace filters strapped to fans. They were quite dark after a few days. The air indoors was noticeably better.
I note that MERV 13 is not HEPA, but is rated for some types of smoke.
So this adds up 
, but I found a source for low-cost filters in the Greater Toronto 
area: FurnaceFiltersGTA.ca in Brampton near Dixie and Steeles. They sell MERV 13’s that they manufacture themselves. In boxes of 12, if you pick them up, they are about 1/3 the cost of a 3M Filtrete at Home Depot. The filters seem well enough constructed, filter material on mesh, pleated; not quite as robust as the 3M filters, the word “adequate” comes to mind. If that means being able to keep 3 filters running in the house instead of 1, that’s a plus in my books.
(FTR I have no commercial relationship with the above company other than as a satisfied customer.)
(Edit: and they are around the corner from the Lindt distribution outlet store on Kennedy in Mississauga 
.)
