Equipment for Kiln Drying Timber

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

"Heat and Vent" type Kilns used to Dry Timber

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

Overhead Fan type kilns

Longitudinal and cross-shaft types

These ulilise a number of fans on a longitudinal driven shaft (below, top) or on one or more shafts running across the kiln (below, lower):-

Image showing air flow in longitudinal and cross shaft timber drying kilns — *Diagrams showing operation of longitudinal (top) and cross-shaft design kilns*

The cross-shaft type is the most popular used in the UK. One or more fans is used to circulate the air through the stickered stack of timber.

Photo showing a small compartment timber drying kiln. Cross shaft type. — *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 Kilns used to Dry Timber

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” when air fails to pass through the stack of timber.

Next Page: The Advantages and Disadvantages of Kiln Drying Timber compared to Air Seasoning Timber.