How To Dry Lumber

Three steps to successful lumber drying.

Nova Dry Kiln provides an official drying manual and technical support for every kiln sold. The simple-to-use procedures are formulated to achieve the best economic results and yet provide the flexibility most kiln operators require for their unique drying demands. To achieve these results, we have defined certain steps that insure our customers of consistently meeting and exceeding high standards in dried lumber.

1. Preconditioning

This optional initial step is used primarily for well air-dried stock or mixtures of green and dry lumber. Preconditioning helps to decrease the moisture difference that can occur in different locations throughout the lumber stack. Our remedy is to load the chamber, then heat it to 110°F for a predetermined time at a low exhaust setting. This allows the transfer of moisture from high-concentration locations to low-concentration locations within each packet of lumber.

2. Drying

The primary processing variables of concern during the drying process are dry bulb temperature and wet bulb depression. Wet bulb depression correlates to the amount of moisture in the air, which in turn correlates to the equilibrium moisture content of the lumber. This parameter tells us something about how quickly the lumber is giving off moisture. By controlling these two process variables in a very precise manner, we can use a pre-selected schedule to achieve the desired end results. The kiln operator adjusts the dry bulb temperature setting and the rate at which moist air is exhausted from the chamber. The steps are executed sequentially.

3. Conditioning

Nova Dry Kiln’s approach to conditioning does not involve the reintroduction of moisture to the chamber. Instead, we trap the moisture that resides in the core of the wood and provide enough time for the lumber moisture gradient to equilibrate. Adding water in the form of steam has traditionally been done to reverse or lessen the effects of lumber case hardening. Since our drying method only slightly case hardens lumber, additional moisture is not needed. The core moisture stress relieves the surface of the wood during conditioning. The lumber equilibrates from the core out in this stage.

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