20x20 Air Filter
Most common size for Corsi-Rosenthal boxes and fan attachments.
- Perfect fan fit
- Easy to find
- Affordable pricing
- Multiple MERV ratings
- Quick replacement
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CR Box UK: Build in 30 mins for under £199 (VAT included). Free UK shipping (2-3 days). True H13 HEPA 2.4x more efficient than Dyson MERV filters. Energy Star 2025 certified. Trusted by NHS, schools & offices.