1.4 Corsi-Rosenthal Build Demonstration

Building an effective air cleaner doesn’t have to be expensive. In this lesson, you’ll learn how to build two proven DIY air filtration systems using readily available materials: a simple single-filter Corsi-Rosenthal unit for smaller rooms and a four-filter Corsi-Rosenthal box for larger living spaces. We’ll cover the recommended materials, walk through each build step, and explain a few design features that can improve performance.

Lesson at a Glance

Commercial HEPA air purifiers can be highly effective, but equipping an entire home with multiple units can become expensive—especially when replacement filters are needed. The Corsi-Rosenthal design provides a proven, low-cost alternative that can deliver excellent air filtration using common box fans and high-quality HVAC filters.

In this lesson, you’ll learn which filters and fans are recommended, compare budget-friendly alternatives, and follow step-by-step demonstrations for building both a single-filter air cleaner and a four-filter Corsi-Rosenthal box. 

Effective air filtration doesn’t have to be expensive. A well-built Corsi-Rosenthal filter can dramatically improve indoor air quality using affordable, readily available materials.

Key Takeaways

  • DIY filtration can provide excellent performance at a fraction of the cost of multiple commercial air purifiers. 
  • Two designs are demonstrated:
    • A single-filter Corsi-Rosenthal unit for bedrooms, home offices, and other smaller occupied spaces.
    • A four-filter Corsi-Rosenthal box for larger living areas requiring greater airflow. 
  • Filter selection matters.
    • Single-filter build: Filtrete 1900 (20×20×4, MERV 13 equivalent)
    • Four-filter build: Filtrete 2500 (20×20×1, MERV 14 equivalent)
    • Nordic Pure filters provide a solid lower-cost alternative. 
  • Fan selection can simplify construction. A fan with a built-in shroud, such as the Vornado recommended in the lesson, eliminates one construction step and improves efficiency. Standard 20-inch box fans can also be used successfully. 
  • Always verify airflow direction before assembling the filter to ensure air flows through the filter before entering the fan. 
  • Seal all joints carefully. Air should pass through the filters—not around them—to maximize filtration performance.

Next Steps

  • Filtration benefits nearly every situation. Unlike isolation and separation, filtration helps reduce airborne particles throughout the home regardless of where contamination may be located.
  • Prioritize occupied spaces. Start with bedrooms and the rooms where people spend the most time, then expand filtration to common living areas.
  • Place filtration strategically. Whenever possible, position filtration between the contamination source and occupied spaces, while avoiding airflow that could disturb contaminated materials.
  • Distribute filtration throughout the home. Multiple units in different rooms are generally more effective than concentrating all filtration in a single location because air continually mixes between spaces.
  • Run filtration continuously. Air cleaners work best when operated continuously, and in general, more filtration provides greater reduction of airborne particles.
  • Choose the filtration level that fits your needs.
    • Bronze: Corsi-Rosenthal Fan Filter (single filter)
    • Silver: Corsi-Rosenthal Box Filter (multiple filters)
    • Gold: Commercial HEPA air purifier
  • Temporary solutions are often sufficient. Because emergency triage is typically short-term, many homeowners choose lower-cost filtration options while they continue investigating the source of contamination.

Build Your Corsi-Rosenthal Box

Gold Standard Build

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Budget Build

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