Three filtration approaches dominate indoor PM control. They solve different versions of the same problem and the right choice depends less on absolute capture efficiency than on what you can deploy where.
HEPA purifiers deliver the highest per-pass filtration (99.97% at 0.3 µm) in a self-contained portable unit. Strengths: best clean-air delivery per dollar in a single room; works in any building; portable. Weaknesses: only filters air in the room it sits in; CADR varies wildly by unit and operating mode; quiet modes are usually too low CADR to matter. Best for: bedrooms, home offices, any room with a sensitive occupant.
MERV-rated HVAC filters filter the air that passes through your central HVAC system, distributing filtration across every conditioned room. Strengths: passive (no separate fan), building-wide coverage, integrates with existing infrastructure. Weaknesses: requires a central HVAC system; higher MERV ratings (13+) can stress older blowers; only filters when the system is actually moving air. Best for: whole-home coverage in homes with adequate HVAC. See MERV ratings.
Corsi-Rosenthal box-fan filters are DIY units using four MERV-13 furnace filters and a 20-inch box fan. Strengths: very high CADR per dollar (often beats commercial units 3x by airflow), serviceable, room-scoped. Weaknesses: visible, louder than commercial units at same CADR, requires assembly. Best for: classrooms, multi-room households on a budget, wildfire-smoke season. Build details. For most households the practical answer is a combination: a HEPA purifier in the bedroom, a MERV-13 in the HVAC, a Corsi-Rosenthal in the family room.
References
- AHAM - CADR program for room air cleaners aham.org
- EPA - Guide to air cleaners in the home www.epa.gov
- ASHRAE 52.2 - Test method for HVAC filter performance www.ashrae.org
- Srebric et al. - DIY box-fan filter performance doi.org
