3. Determine Drying Temperatures

Kiln theory and knowledge

How does a standard kiln w...
Kiln drying related public...
Kiln Drying Associations
Understanding the Extended...
Why dry lumber?
Drying defect and causes
Steaming lumber.
Direct gas heating for kilns.
Power venting.
Moveable between-deck.

All subjects

Shop online easy

3. Determine Drying Temperatures

Developing a drying schedule based on a 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.

We hope this information meets with your expectation and approval. We always welcome your opinions and suggestions. Feel free to email us anytime.

Reinventing ourselves and our kiln designs

Serving you, your company and the industry better by reinventing ourselves. Find out about our new kiln designs and why you should buy from us. Sign up for a newsletter or request additional information about our latest innovations.

On-line store

Kiln controllers, fans, sensors, vents, heat systems and more