How long to Heat treat?

Detailed answer:

As mentioned above this is a rather difficult question to answer without specific information about the pallet. Even then we have a hard time estimating the actual heat treatment time. Below we have listed the factors that has an influence on the treatment time and the theory behind this.

Major factors that determine the treatment time:

Initial starting temperature
This is obvious, but lets examine it a little. We will take water as a standard for this example.
It takes one BTU to heat one pound of water one degree
The same is true for pallets as well not taking the energy waste into account. If it takes 2 million BTU's (586kw) to raise the temperature from 85F to 135F in a load of pallets, it will take 4 million BTU's (1172kw) to raise the temperature from 35F to 135F. Why? The temperature differential from 135 to 85 is 50 degrees and the temperature differential from 135 to 35 is 100 degrees; twice as much difference means twice as much energy is needed.

Thickness of the largest piece of wood in the pallet.
This is obvious as well and based on our experience it seems like the length of the heat treatment time will increase propotionately with the thickness of the wood. You can compensate some by increasing the chamber temperature. A pallet with thicker wood (such as a block pallet) will not necessarily need more energy. Therefore, it will allow the heating system to achieve a higher chamber temperature faster, since the pallet consumes less energy per hour.

Size of the heat source.
The heat source is a little like a bottle neck, either it provides enough heat and the process is not slowed or it is not able to provide sufficient heat. However, in the very beginning of the process the size of the heat source is directly related to the speed with which the pallets are heated. The thinner the largest wood piece is on your pallets the more the latter statement is true.

Adequate air flow.
The air in the kiln acts as the heat transfer agent between the heating source and the pallets. As the air becomes more humid it is able to carry more energy to the pallets per cubic foot/meter of air. This is one of the reasons it is desireable to have a very well sealed chamber (the other is to achieve a high humidity to avoid drying defects). Adequate air flow means not too little and not too much. Too much air flow may actually dry the pallet during the initial heat up period when the air has not become saturated with moisture. As part of the air flow equation one should also consider the lenght of air travel from entering the pallets to existing. Naturally the pallets on the existing side will recieve less heat and reach the required treatment temperature last. Reversing the fans may help reduce this problem. It is our experience that 40-50 feet is maximum when using reversing fans.