Corsi–Rosenthal XXL (24 V Blower Edition)
A high-flow, high-static-pressure MERV-13 cube with a quiet 24 V centrifugal blower, 12/24 V DC input (buck/boost), and a CO₂ meter pocket to track ventilation. Built for wildfire smoke and dusty urban air.
What this is
- Four to six MERV-13 pleated filters form a low-resistance intake cube.
- A 24 V DC centrifugal blower pulls air through the cube (better static pressure than an axial fan for loaded filters).
- A wide-input DC buck/boost regulates 24 V from 12–30 V sources (power station, vehicle, solar-battery).
- A side CO₂ meter pocket holds a portable meter to check room ventilation (CO₂ ≠ smoke; it’s a ventilation proxy).
Science notes: MERV-13 is recommended for smoke & fine aerosols; CR-boxes are validated in lab/field studies; CO₂ helps judge fresh-air rates, not filter performance.
Target performance
| Flow (clean filters) | ~450–800+ m³/h (260–470+ CFM) depending on filter area & blower |
|---|---|
| Noise | Low-mid hum; centrifugal = better tone than box fans |
| Power | 60–180 W typical @ 24 V |
| Use cases | Wildfire smoke, urban PM2.5, pollen/dust, classroom/garage studios |
Bill of Materials
Core filtration & frame
| MERV-13 filters | 4–6× 20″×20″×4″ pleated (4″ lowers pressure drop). Arrow points inward. |
|---|---|
| Base/top | Double-wall cardboard (or ¼″ plywood/HDPE) for floor & top plenum. |
| Seal | Foil HVAC tape + painter’s tape; optional weatherstrip foam for edges. |
| Spine | Aluminum angle or 2020 extrusion for stiff corners (optional but nice). |
Blower + power
| 24 V centrifugal blower | Back-curved, ≥250–400 CFM @ ≥0.3–0.6 in H₂O static; 24 V, ≤10 A. |
|---|---|
| DC-DC buck/boost | Wide input (9–36 V) → regulated 24 V, ≥10 A continuous, efficiency ≥90%. |
| Inline fuse | MIDI/ANL or blade fuse at source (1.25× blower max current). |
| Connector | Anderson SB50 or XT60 panel jack; 16–12 AWG DC wire; ferrules & heat-shrink. |
| Switch | DC rated rocker (≥30 VDC, ≥15–20 A) or plug-unplug via SB50. |
Controls & pocket
| Speed control | PWM motor controller for 24 V blowers (≥15 kHz preferred) or simple 2-speed selector (voltage steps). |
|---|---|
| CO₂ meter pocket | Clear pouch (Velcro) sized for portable meter; slit for sensor vents. |
| Feet & handles | Rubber feet (vibe control), strap handles or side cut-outs. |
| Fasteners | Self-tapping screws for blower flange, corner brackets for rigidity. |
| Safety | Mesh guard over blower intake; “Airflow” arrow labels; no ionizers/ozone. |
CO₂ meter is for ventilation insight; it does not measure smoke. Filters reduce PM; CO₂ tells you how much fresh outside air is mixing in.
Tools
Utility knife, straightedge, square, duct/foil tape, screwdriver/drill, step bit (for panel jack), crimper, multimeter, optional hot-glue for tacking corners.
Wiring (DC)
DC SOURCE (+) → FUSE (near source) → SB50/XT60 panel → DC-DC buck/boost (24 V out) → Switch → Blower (+)
DC SOURCE (−) → SB50/XT60 (−) → Buck/boost (−) → Blower (−)
Speed control:
• Preferred: 24 V PWM motor controller (≥15 kHz) between switch and blower (+/−).
• Simple: Two-position switch selecting 18 V (low) / 24 V (high) via buck presets.
Wire: 16 AWG up to ~8 A, 14–12 AWG for higher draws or longer runs. Strain-relief every panel pass-through.
Assembly — Step by Step
- Dry-fit the cube. Stand 4–6 filters upright in a ring (arrows pointing inward). Square the corners.
- Tape the seams. Foil/HVAC tape outside seams top→bottom. Add interior painter’s tape tabs to hold shape (optional).
- Add the floor. Trace cube onto cardboard/ply base; cut; tape tightly so air only enters through filters.
- Top plenum & blower cutout. Cut a top panel that covers the cube. Mark a circle/rectangle for the blower outlet. Cut opening; pre-drill blower flange holes.
- Mount the blower. Screw the blower to the top plenum. Add weatherstrip foam between flange and panel for a seal. Fit a mesh guard over the blower intake.
- Stiffen (optional but recommended). Screw short aluminum angles inside two corners; add a cross-strap under the base as a handle.
- Panel jack & switch. Drill for SB50/XT60 and rocker switch. Label 24 V IN and ON/OFF. Mount buck/boost inside a protected corner with airflow clearance.
- Wire it. Source → fuse → panel jack → buck/boost (24 V) → switch → blower. Keep polarities straight; crimp, no tinned leads. Zip-tie harnesses.
- CO₂ pocket. Tape/Velcro a clear pouch on the outside near the outlet (not blocking it). Meter vents exposed; cable slot if rechargeable.
- Seal check. Run a bead of tape on every seam (inside corners too). Any leak = lost CADR. Shroud gaps if you see recirculation around the outlet.
- Smoke test. Power up outdoors; incense on intake side, watch for strong draw & no bypass. Indoors, place a PM2.5 meter up/downstream to verify drop.
Use & Tuning
- Run on high for first 15–30 min to purge, then set to comfort/noise level.
- For wildfire days, close doors/windows; replace filters sooner (visual loading = swap).
- CO₂ guide: sustained readings >800 ppm suggest more fresh air is needed (openable window, higher HVAC outdoor air) — filtration won’t lower CO₂.
Tip: Two smaller units in corners often beat one big unit for uniform room mixing.
Runtime & Current (quick calc)
| Example | 24 V blower @ 120 W → current ≈ 5 A |
|---|---|
| Battery 24 V 20 Ah (≈480 Wh) | ~3.6 h @ 120 W (assume 90% eff.) |
| Battery 24 V 50 Ah (≈1200 Wh) | ~9 h @ 120 W (90% eff.) |
Fuse ≈ 1.25× max current (e.g., 10 A max → 12–15 A fuse). Check wire drop for long leads.
Hazards & Safety
- Ozone/ionizers: Do not add ozone or ionizer modules. They can emit lung irritants and are not needed for particulate removal.
- Electrical: Fuse at the source; use DC-rated switch; insulate all connections; add strain relief at panel jacks.
- Fire: Keep intake/exhaust clear; never cover outlet; don’t run unattended on unstable surfaces.
- Filters: MERV-13 captures fine PM, but they load up faster in smoke—inspect weekly during events.
- CO₂ meter: It tracks ventilation (exhaled air), not smoke concentration. Use a PM2.5 meter to track smoke removal.
Why a 24 V Blower?
Centrifugal (back-curved) blowers sustain airflow against the higher resistance of a multi-filter cube and loaded media, where axial/box fans fall off. That static-pressure advantage keeps your CADR steadier as filters clog. Choose a blower with a published fan curve and aim for ≥0.3–0.6 in H₂O capability at your target flow.
Pre-Flight Checklist (Print)
Mechanical
- All seams sealed (inside & out)
- Blower screws tight; mesh guard on
- Feet stable; handles secure
Electrical
- Polarity correct; fuse at source
- 24 V present under load
- Speed control set; no hot wires
Function
- Strong intake on every face
- No bypass leaks at corners
- PM2.5 drops after 5–10 min
Maintenance
- Vacuum pre-dust off the upstream side; replace when visibly loaded or flow/noise shifts.
- Wipe blower blades seasonally; check for wobble or debris.
- Re-tape seams after filter changes; label change dates.
Sources (overview)
- EPA & CDC: MERV-13 for smoke; ventilation & CO₂ monitor guidance; ozone warnings.
- UC Davis & Clean Air Crew: CR-box build methodology & sealing tips.
- Peer-reviewed studies: DIY air cleaner CADR & smoke reduction performance.
- Fan engineering notes: centrifugal vs axial static-pressure behavior.
Full linked citations provided with the article post.