Building a Mini Filter
Students will be able to:
- Build a simple DIY air filter using a box fan and furnace filter
- Explain how the fan and filter work together
- Follow step-by-step engineering instructions
- Test the effectiveness of their air filter
"Can we build our own air cleaner?"
During the COVID-19 pandemic, scientists Dr. Richard Corsi and Jim Rosenthal invented a simple, cheap air cleaner that anyone can build. It uses a box fan and furnace filters - that's it! These "CR Boxes" are now used in schools, offices, and homes around the world!
For a Simple Single-Filter Version:
- 1 box fan (20" x 20" works best)
- 1 furnace filter (20" x 20" x 1" or 2", MERV 13 recommended)
- Duct tape or bungee cords
- Cardboard to seal gaps (optional)
For a Full CR Box (4 filters):
- 1 box fan (20" x 20")
- 4 furnace filters (20" x 20" x 2", MERV 13)
- Duct tape
- Cardboard for the bottom
Step 1: Find the Arrow
Look at the edge of the filter - there's an arrow showing airflow direction. The arrow should point TOWARD the fan (air goes through filter THEN through fan).
Step 2: Position the Filter
Place the filter against the BACK of the fan (the side that sucks in air, not the side that blows out).
Step 3: Attach the Filter
Use duct tape or bungee cords to secure the filter to the fan. Make sure there are no gaps where air can sneak around the filter!
Step 4: Seal Gaps
Use tape or cardboard to cover any gaps between the filter and fan. All air should go THROUGH the filter!
Step 5: Test It!
Turn on the fan. Put your hand behind the filter - can you feel it pulling air through? If yes, it's working!
1. Fan Pulls Air
The box fan creates suction that pulls room air toward it
2. Filter Catches Particles
Air passes through the filter, leaving particles trapped behind
3. Clean Air Exits
Cleaned air blows out the front of the fan into the room
Does It Really Work?
If you have a PM sensor or CO2 sensor, you can test your air cleaner!
- Before: Record the PM2.5 or particle level in the room
- Turn on: Run your DIY air cleaner for 15-20 minutes
- After: Record the PM2.5 or particle level again
- Compare: Did the particle level go down?
What Should Happen
If your air cleaner is working well, PM2.5 levels should drop! A good CR box can clean the air in a classroom-sized room in about 10-15 minutes.
Important!
- Always have an adult help with building
- Never block the fan blades
- Keep the fan away from water
- Don't run the fan unattended for long periods
- Replace the filter when it gets dirty (check monthly!)
- Keep cords away from walking areas
| Air Cleaner | Cost | Notes |
|---|---|---|
| Commercial HEPA air purifier | $150-500 | Quieter, looks nicer |
| DIY CR Box (4 filters) | $50-80 | Same cleaning power! |
| Simple fan + filter | $30-50 | Good starter option |
Amazing fact: The DIY version often cleans MORE air per dollar than expensive store-bought purifiers!
Document your build:
- Draw a diagram of your air cleaner showing how air flows through it
- Label: fan, filter, direction of airflow, where particles get trapped
- If you tested it: record your before and after measurements
- What would you do differently next time?
- Where would be a good place to use this air cleaner?
Key Takeaways
- You can build an effective air cleaner with just a fan and filter!
- The fan pulls air through the filter, trapping particles
- MERV 13 filters catch most PM2.5 particles
- DIY air cleaners can be just as effective as expensive store-bought ones
- Anyone can help clean the air - you don't need to be an expert!
Corsi-Rosenthal Box
A DIY air cleaner made from a box fan and furnace filters, invented during COVID-19.
DIY
"Do It Yourself" - making something on your own instead of buying it.
Airflow Direction
The way air moves through a filter or system, shown by arrows on filters.
Seal
To close gaps so air doesn't leak around the filter.