Updated: Oct 22
It is a very common ordeal to confuse heat treated lumber with kiln dried lumber. Both terms are often used synonymously, but why? Is there an actual difference?
To answer these questions we first must know the purposes for each.
So why heat treat lumber?
Simply put, lumber is heat treated to kill pests living inside of the lumber. These pests need to be eradicated to keep them from finding a new home after the lumber has been transported from one country to another. Invasive pests residing in the U.S. such as the Emerald Ash Borer and the Asian Longhorned Beetle are prime examples of how invasive pests have hitched a ride on a lumber caravan.
What is the purpose of kiln drying lumber?
The purpose of kiln drying is to reduce the inner moisture content of freshly cut green lumber. Freshly cut green timbers can harbor up to 50% moisture content. An example of why moisture content within wood can be crucial would be home construction. Homes are built with kiln dried lumber to prevent shrinking, warping, checking, cracking, mold, etc. Without depleting lumber of its moisture, the lumber itself is subject to the gradual changes overtime that come with air drying.
How is wood heat treated and how is it kiln dried?
The process of heat treating takes place within a heat treating chamber. These chambers typically can hold about a semi truck load’s worth of lumber. Lumber as well as wooden pallets will stay in the chamber for an extended amount of time, which can depend on variables such as the thickness of the components, the amount of board feet in the chamber, and how the pallets or lumber is stacked.With the chamber in cycle, the internal temperature of the thickest component in a pallet must reach 140 degrees fahrenheit for 30 consecutive minutes. Once achieved, the pallets are ready for export. Measuring the temperature of the inside of the pallets wooden components is done by using electronic thermometers that are placed in pencil like holes that have been drilled into the wooden components.
Why are heat treating and kiln drying so often confused?
Most pallet users often confuse having a heat treated pallet with having a kiln dried pallet. Though heat treating a pallet that was built with green wet lumber can help to speed up the drying process, the pallet itself still harbors more moisture than a pallet built with kiln dried lumber. The fact that both heat treated lumber and kiln dried lumber are put into heated “chambers” is usually the reason for confusion. Heat treating is to kill bugs, kiln drying is to take away moisture.
Why does it matter to pallet buyers?
Just because a pallet is heat treated, it does not mean that there are low levels of moisture within the wood, and just because a pallet is built with kiln dried material does not mean that it automatically qualifies for export without proper stamping identification. Pallets built with kiln dried material that also need to be ISPM15 qualified still need to have heat treat stamps
added to the finished product.
Something else to keep in mind is that oftentimes softwood pallet lumber that is kiln dried is more expensive than green hardwood pallet lumber. Many factors can affect which lumber market is more costly at any given point in time. For different industries such as those with food grade facilities, pallet requirements demand pallets to be dry with no mold. For them, kiln dried lumber is the way to go. For other manufacturers or industries that store their product and pallets outside, having dry pallets or clean pallets may be an unnecessary cost.