TL;DR
Uneven drying is usually caused by poor airflow through the stack. Verify fan direction, sticker alignment, and venting schedule against the lumber species schedule.
What you might see
- high moisture variation between boards in same charge
- wet pockets in center of stacks
- ovendry samples showing wide MC spread
- surface checking on boards that dried faster
Likely causes
Uneven airflow through the stack from misaligned stickers or bulging lumber
Fan running in the wrong direction for the current drying phase
Incorrect vent schedule for the species and starting moisture content
Sample board placement not representative of the stack wet zones
Required tools
- Pin or pinless moisture meter
- Nyle L200 kiln schedule for species
- Tape measure for sticker alignment check
Safety first
- Do not enter the kiln while fans are running or while heat is active. Kiln interiors reach temperatures above 70 deg C.
- Wood dust accumulation inside kilns is a fire hazard. Remove debris before starting a new charge.
Procedure
- 1
Pull the moisture content readings from all sample boards and map them by stack position to identify which zones are drying slowly.[1]
- 2
Verify the fan rotation direction matches the schedule for the current drying phase. Consult the Nyle L200 kiln schedule for the species being dried.
- 3
Open the kiln after the charge cools and inspect sticker alignment. Stickers should be vertically aligned across all layers. Offset stickers block airflow channels.
Warning: Do not enter the kiln while fans are running or while steam or heat is active. Kiln interiors are hot and fans create hazardous air movement. - 4
Check for boards that have bowed or cupped and are blocking the airflow channels. Restack if needed before returning the charge.[1]
- 5
Review the vent schedule. For high-MC green lumber, insufficient venting in the early phase slows drying of the interior.
- 6
Add sample boards to the wet zones identified in step 1 and re-run the charge or extend the drying time.
- 7
Log the charge parameters and final MC spread for future schedule refinement.
Sources
Nyle Systems Nyle L200 Lumber Drying Kiln general technical documentation, Nyle Systems
Lumber kiln drying schedules and airflow management, general wood drying practice (general)
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