3. Determine Drying Temperatures Home Kiln theory Basic theory Kiln schedules based on drying gradient

Developing drying programs/schedules is a continuing process of trying to perfect the drying quality and the efficiency of the kilns. On some occasions the same specie will require a little different drying schedule if it comes from a different region. One example is the difference between oak grown in warmer climates and oak grown in colder climates.

Finding the right temperature schedule.

In most cases finding the correct temperature for drying is a choice between:

Lower temperature/Higher RH%:	Slower drying Less degrade Better color in some species.
Higher temperature/Lower RH%:	Faster drying A little more degrade Little darker color in some species.
It should be noted:	In some species it is desirable to reach a high temperature at the end of the drying cycle to kill insects, set (crystalize) the resin; or in oily specie, to even out the color a little. On a few species it may improve the quality to operate at a higher temperature for a short period of time to kill any stain or mold in the lumber. This is often used on Yellow Poplar in North America. The same practice is used on Beech in Europe; normally in a steam chamber.

As a general rule the following temperature for most hardwood species can be used:

Over 25%MC (predrying phase):

Slow and careful drying for best color

25 C or 80 F

Medium and normal drying

28 C or 85 F

Faster drying (not color sensitive species)

35 C or 95 F

Slow and careful drying for best color

45-50 C or
115-125 F

Medium and normal drying

50-65 C or
125-150 F

Faster drying (not color sensitive species)

65-80 C or
150-175 F

On several species, especially tropical woods, the temperature schedules are higher than our normal drying pattern. In this case we suggest you study existing publications and use the temperature and RH% settings.

Caution:

Older drying programs/schedules normally use higher temperatures and lower relative humidity due to insufficient air flow and venting in older kilns.
YOU SHOULD ALWAYS REDUCE THE TEMPERATURE SOME AND RAISE THE RH% FROM THE OLDER DRYING PROGRAM/SCHEDULE FOR SAFETY.
Later you can increase the drying pressure if it seems to be drying slower than the recommended safe rate.

3. Determine Drying Temperatures Home Kiln theory Basic theory Kiln schedules based on drying gradient

Finding the right temperature schedule.

As a general rule the following temperature for most hardwood species can be used:

Upcoming events