Forest Products Notes on...

Timber Kiln Drying Equipment

The commonest type of timber drying kilns are “heat and vent” type “compartment kilns” which dry timber in batches:

Heat and Vent timber kilns

These can be categorised by the location of the fans used to circulate the air. Thus there are:

Overhead Fan type timber kilns:-

Longitudinal shaft type (below): utilising a number of fans on a longitudinal, driven shaft.

Diagrams showing operation of longitudinal (above) and cross shaft design kilns

Cross shaft type (above):- this type is the most popular in UK. One or more fans is used to circulate the air through the stickered stack of timber.

A 3m3 capacity overhead cross-shaft fan type kiln. The air entry/ exhaust ducts are just visible in the back wall of the kiln, on either side of the air circulation fan.

Side Fan type: these are also popular:-

Construction of Timber Drying Kilns

Originally, compartment kilns were built of brick (cavity-wall), but these suffered from mortar degradation due to the acids released from the wood. Nowadays, they are usually constructed from double skinned sheet aluminium or steel, well insulated with glass wool. From a point of view of energy conservation it is imperative that there are good seals around the doors. The fans can be external or internal.

Kilns should always be run full to reduce air "short-circuiting” and not passing through the stack of timber.

The NEXT PAGE of these notes is our most popular page, as it compares air seasoning of timber with kiln drying of timber and in particular the Advantages and Disadvantages of Air Seasoning of Timber compared to Kiln Drying...

Diagrams showing operation of longitudinal and cross shaft design kilns.

A 3m3 capacity overhead cross-shaft fan type timber kiln.

Drying timber showing fan at side of timber stack.

Image of Advantages and Disadvantages of Air Seasoning of Timber compared to Kiln Drying Page

To learn more about the theory underpinning kiln drying of timber (temperature, relative humidity and airflow see the PREVIOUS PAGE: Kiln Drying of Timber

Reasons to Dry Timber: An Introduction to Timber Drying Timber Drying - Fundamentals Concepts and Definitions Factors controlling the Drying of Wood The Structures of Softwoods and Hardwoods and their effect on Wood Drying An Introduction to the Air Seasoning of Timber Layout of a Timber Drying Yard Design of Stacks in the Timber Drying Yard Kiln Drying of Timber Types of Kiln Drying Equipment Benefits of Kiln Dried Timber production compared to Air Seasoning Timber Using a Dehumidifier to Dry Wood High Temperature Timber Drying Solar Kilns for Drying Timber Drying Defects in Sawn Timber Case Hardening of Timber Avoiding Case Hardening by Monitoring the Drying of Timber. Also Collapse & Staining of Timber