Box fan filters are great. The fans aren't really designed to operate with much load, so I had issues with the motors burning up eventually (3-12mo) when trying

Box fan filters are great. The fans aren't really designed to operate with much load, so I had issues with the motors burning up eventually (3-12mo) when trying to force air through too fine of a filter (somewhere around merv 15 iirc, taped at the edges to prevent air from going around). In college I had a _really_ cheap flat, and all my neighbors were chain smokers. I didn't realize quite how bad it was in my apartment (large gaps under the door, etc) till a classmate pulled me aside and asked how long I'd been smoking -- apparently the residue on my clothes was easy for anyone with a functioning nose to recognize when I walked nearby. Long story short, box fan filters completely fixed that problem, and as an added benefit you could set one up next to any cooking disasters and watch the smoke get pulled from the air.