Measuring Recirculation With a Smoke Pencil

Recirculation — exhaust air folding back into intake — is the silent hashboard killer in small Korean garages. Pool uptime looks fine while junction temps creep over weeks.

Tools

• Battery smoke pencil or small fog machine rated for HVAC use
• Manometer or smartphone pitot app calibrated against our reference tube
• Camera for video the client can show installers

Procedure

1. Seal incidental leaks — Close doors you intend closed during operation. Note window grilles you cannot seal; they become intake lanes in the sketch.
2. Run miners at production fan profile — Not firmware test mode; real pool connection, typical clock.
3. Release tracer at exhaust outlet — Watch whether stream bends toward intake within two seconds. Any bend exceeding 30° toward intake flags a recirculation lane.
4. Walk the aisle — Tracer at hashboard height, mid-aisle. Stagnant pockets show where no rack should sit.
5. Mark zones — Green intake lane, red exhaust lane, yellow transition. Yellow is where baffles or duct extensions earn their cost.

Limits

Smoke pencils lie in very humid summer weeks — water vapor can mimic recirculation. We repeat tests morning and afternoon on humid days.

When to hire vs DIY

Operators with a single unit and one intake grille can learn this method. Farms above three units in tight rooms benefit from a third observer and our annotated photos for permit discussions.