The Corsi-Rosenthal box is a DIY air purifier invented in 2020: four or five furnace filters taped into a cube with a box fan on top. It moves a huge volume of air through cheap MERV-13 media, and independent testing repeatedly shows it rivalling purifiers costing many times more. For a London home fighting traffic PM2.5, it's the best value in clean air — full stop.
You can build one yourself, or buy the same physics pre-engineered, balanced and quieter as a Luggables kit.
Ready to clean up your London air?
Luggable MERV-13 kits deliver up to 681 m³/h CADR — built on the Corsi-Rosenthal principle, from £229. Ships from Oxford in 2–3 days.
Shop the UK store → See all kitsWhat you need to build one
- 4–5 × MERV-13 furnace filters (a taller five-filter cube moves more air)
- 1 × 20-inch box fan (or a PC-fan array for lower noise)
- Cardboard base + a cardboard "shroud" to reduce dead space over the fan
- Foil tape
Total DIY cost is roughly £60–£120 depending on filters. It takes about 20 minutes.
CADR and cost, compared
| DIY CR box | Luggables kit | £500 sealed unit | |
|---|---|---|---|
| CADR | ~350–600 m³/h | 369–681 m³/h | ~200–400 m³/h |
| Noise | Box-fan hum | Under 40 dB | Low |
| Filter type | Standard MERV-13 | Standard MERV-13 | Often proprietary |
| Upfront | £60–£120 | £229–£279 | £400–£700 |
Frequently asked questions
Is a Corsi-Rosenthal box as good as a real air purifier?
On clean-air delivery it often outperforms purifiers costing far more, because it moves so much air. The trade-offs are size, box-fan noise and looks — which pre-built kits solve.
What MERV rating should the filters be?
MERV-13. It captures fine PM2.5 while keeping airflow high. Lower MERV lets particles through; true HEPA chokes the airflow of a box fan.