Oak kiln charge: what fits, and how far it moves
Charge volume for a stack of 32 mm oak, the moisture content it settles at in a workshop, and how much a 200 mm board shrinks getting there.
The job
A small hardwood kiln has a usable stack envelope of 6.0 × 1.8 × 2.4 m. Before loading, the operator needs three numbers: how much oak actually goes in, what moisture content the boards will settle at in the customer's workshop, and how far a wide flat-sawn board will move on the way there.
Inputs
| Item | Value |
|---|---|
| Stack envelope (L × W × H) | 6.0 × 1.8 × 2.4 m |
| Board thickness | 32 mm |
| Sticker thickness | 25 mm |
| Stack fill factor | 0.90 |
| Storage climate | 20 °C / 65% RH |
How it was calculated
Charge capacity uses the stack geometry from the Dry Kiln Operator's Manual (USDA AH-188): wood volume = stack volume × t / (t + s) × fill factor, with t the board thickness and s the sticker thickness. Equilibrium moisture content uses the Hailwood–Horrobin sorption equation in the Simpson form printed in the Wood Handbook 2021. Shrinkage uses the published tangential coefficient for white oak between fibre saturation and the target moisture content.
What the calculators return
| Item | Value |
|---|---|
| Wood per charge | 13.10 m³ |
| Board feet per charge | 5,550 |
| Wood fraction of the stack | 56.1% |
| Equilibrium moisture content in store | 12.0% |
| 200 mm tangential board at target MC | 184.6 mm (−7.7%) |
Compared with the usual approach
| Item | 25 mm stickers | 19 mm stickers |
|---|---|---|
| Wood per charge | 13.10 m³ | 14.64 m³ |
| Wood fraction of the stack | 56.1% | 62.7% |
| Difference per charge | — | +1.54 m³ (+11.8%) |
Every number on this page is recomputed at build time by the calculators themselves — nothing is typed in by hand.
Takeaway
Sticker thickness is not a detail. Going from 25 mm to 19 mm stickers puts over one and a half extra cubic metres of oak in the same chamber — about 12% more per charge, every charge, for the price of a different batch of stickers. The trade-off is real though: thinner stickers slow air movement and raise the risk of uneven drying, so weigh capacity against degrade rather than treating the bigger number as free. And a 200 mm flat-sawn oak board that measures right off the kiln will be several millimetres narrower once it reaches workshop equilibrium — size the joint for the settled dimension, not the wet one.