Airflow Mapping for Dry Rooms: A Simple SOP to Kill Hot Spots

Goal: even, gentle airflow through the room so every hanger or rack dries at the same rate—no crispy outsides, no wet cores, no mold pockets.

Tools you’ll need

• Smoke pencil or incense sticks

• 1–2 lightweight tape flags or tissue strips per rack/hanger

• Handheld anemometer (reads ft/min or m/s)

• Hygrometer/thermo (data-logging preferred) at door, center, far corner, and return

• Blue painter’s tape + marker (to label zones)

• Floor plan printout (or tape a rough map to the wall)

Targets to aim for

• Air speed at canopy: ~ 20–60 ft/min (0.1–0.3 m/s) measured between hanging rows

• Air changes per hour (ACH): 6–12 (gentle turnover, not wind tunnel)

• No direct blast on flower. Flags should flutter, not flap

• Room delta: temp and RH spread ≤ 2°F and ≤ 3% RH across all sensors

• Path: air should move from clean intake → across canopy → to return without short-circuiting

If any value is out of range, adjust and re-check before loading a harvest.

10-minute pre-flight check (do this every morning during dry)

1. Open the log sheet; write date/time, batch IDs in room.

2. Verify setpoints on HVAC/dehu: temp 60–68°F, RH 55–60% (or your house spec).

3. Check dehu drain and filters; empty/purge if needed.

4. Walk the room: doors closed, lights low, fans on.

5. Confirm flags/tissue are still taped and visible in each aisle.

6. Read and record door/center/far-corner/return temp & RH.

7. If delta > 2°F/3% RH, move to “Tune & Fix” section below.

8. Make one pass with smoke pencil down each aisle—note dead spots or eddies.

9. Record any smell of stagnant air or cool damp “pockets.”

10. Sign off; note any changes you made.

First-time airflow mapping (new room or after equipment changes)

A. Mark the room

• Tape a quick map to the wall.

• Label INT (intake), RET (return), D1/D2 (doors), aisles A–D, and racks 1–10.

• Number each hanger bay (e.g., A-3, B-7) so notes are consistent.

B. Flag the canopy

• Tape a small tissue strip at chest height on every other rack end.

• Ideal motion = steady, light ripple; no whipping.

C. Measure baseline

• In the center of each aisle, hold the anemometer at canopy height; record ft/min.

• Take temp/RH at the four sensor stations and note deltas.

D. Smoke test

• With doors closed, trace a straight line from intake to return down each aisle.

• Watch smoke at tees and intersections—mark any spot where smoke stalls, spins, or jumps directly into the return.

Tune & fix (fastest changes first)

1) Fan aiming & speeds

• Aim circulation fans parallel to aisles, not at buds.

• Drop speed one step if flags flap; raise one step if flags hang still.

• Add small “booster” fans only in dead aisles; set to the lowest speed.

2) Balance the push–pull

• If the return is sucking air straight from the intake, redirect with a short baffle or turn the nearest fan away from the return.

• If the far corner is stale, reduce CFM near the return before adding new CFM (prevents short-circuiting).

3) Create a gentle loop

• Think HAF (horizontal airflow) like greenhouses: a slow, continuous loop.

• Point end-aisle fans so air turns the corner and keeps moving.

4) Even the load

• If one wall dries faster, that wall has more air speed. Redistribute hangers or slide racks to open narrow choke points.

5) Dehu & HVAC placement

• Don’t blow conditioned air directly on flower.

• If a supply registers too strong, deflect with a simple clip-on diffuser or louver adjustment.

Acceptance criteria (sign off before loading a big harvest)

• All aisle readings 20–60 ft/min; no reading = 0 ft/min dead zone.

• Tissue flags ripple lightly—none pinned straight out.

• Temp spread ≤ 2°F; RH spread ≤ 3% across the room.

• Smoke shows a clean path from intake → through canopy → to return.

• Notes logged; map updated with final fan aims and speeds.

Daily drying SOP (copy/paste)

• AM check (10 min): record four RH/Temp points; scan flags; quick smoke pass.

• If RH delta > 3%:

  • Reduce fan near return one notch; re-check.

  • Add a low-speed booster only in the slow corner; re-check.

• If flags flap anywhere: drop that fan’s speed or re-aim parallel.

• If tissue hangs limp: increase nearby fan one notch or open a choke point.

• End of day: log notes, photograph flag motion in worst aisle for history.

Common problems & quick cures

• Crispy outsides, damp cores → Air too fast across surface. Lower fan speed one step; raise room RH 2–3% for 12–24h, then resume.

• Slow, uneven dry near the door → Door leakage/short-circuit. Weather-strip or add a sweep; keep doors closed.

• Mildew smell in one corner → Dead zone. Add a low-speed booster and turn adjacent fan away from return.

• Big RH swings → Equipment oversizing or too much CFM. Lower circulation speed, let HVAC do the drying, not box fans.

Verification before cure & storage

• Randomly probe several stems—all bend then gently snap.

• Room sensors show stable RH with doors closed for 30–60 min.

• (Optional) If you use water-activity testing, spot-check representative bins before sealing for storage.

Record-keeping (what to log every run)

• Batch IDs, load date/time, hang density (lbs per rack), fan settings, setpoints.

• Four-point Temp/RH daily, plus any anemometer spot checks.

• Any changes (fan aim/speed, added boosters, baffles).

• Problem notes + fix + outcome.

• Final QC (snap test, any lab checks).

Setup cheat sheet (post this on the door)

• Fans parallel to aisles, low speed, no direct blast on buds.

• Flags every other rack; anemometer check once per aisle.

• Intake to return path clear—no pallets or carts blocking corners.

• Doors closed during dry; open only for quick work.

• Target canopy speed: 20–60 ft/min. Delta limits: ≤2°F / ≤3% RH.