Corsi-Rosenthal Box (DIY) Review
by DIY
~$90 for build materials
Estimated Annual Filter Cost: ~$40-$80/year
Summary
A properly built DIY Corsi-Rosenthal Box offers the best clean-air bang for the buck: ~274 CFM (Cubic Feet per Minute) (or higher with deeper filters) for about $90 in parts and no ozone risk. It’s a stellar smoke-season or classroom stopgap for spaces up to ~450 ft². Expect box-fan noise and a big footprint, but if you’re handy with duct tape you’ll match—or even beat—mid-priced HEPA (High Efficiency Particulate Air) towers at a fraction of the cost.
Here's what this purifier does best
- Ultra-low cost per CFM (Cubic Feet per Minute): ~$0.22 per CFM makes commercial units look pricey
- Proven virus capture: EPA tests found 99% removal of airborne virus in 60 min.
- Easy-to-source filters: Any 20″ MERV-13 HVAC panel works—no proprietary cartridges.
- Huge airflow on high: DIYers have measured 600+ CFM with shrouds and deep filters.
- Zero ozone, no gadgets: Pure mechanical filtration—safe for sensitive lungs and simple to repair.
Consider these trade-offs
- Noticeable fan noise: 49–61 dB even on low—light sleepers may object.
- Bulky “duct-tape cube” look: Not décor-friendly; takes ~4 sq ft of floor space.
- Performance varies: Air-tight taping, shroud, and filter depth all affect CADR (Clean Air Delivery Rate).
- Manual operation only: No auto mode, AQI (Air Quality Index) read-out, or timer.
- Rebuild to change filters: Swapping panels means cutting tape and reassembling the box.