United States

Department of

Agriculture

Forest Service

Southern 

Research Station

General Technical 

Report SRSÐ 134

DESIGN AND OPERATION OF A 

SOLAR-HEATED DRY KILN FOR 

TROPICAL LATITUDES

Brian Bond, Omar Espinoza, and Philip Araman
January 2011 

Southern Research Station 

200 W.T. Weaver Blvd. 

Asheville, NC 28804

Authors:

Brian Bond, Associate Professor and Extension Specialist, Omar 

Espinoza, Postdoctoral Associate, Virginia Polytechnic Institute and 

State University, Department of Wood Science and Forest Products, 

Blacksburg, VA 24060; and Philip Araman, Wood Scientist and 

Research Team Leader, U.S. Department of Agriculture, Forest Service, 

Southern Research Station, Blacksburg, VA 24060.

Product Disclaimer

The use of trade or firm names in this publication is for reader information and does not imply 

endorsement by the U.S. Department of Agriculture of any product or service.
Design and Operation of a Solar-Heated 

Dry Kiln for Tropical Latitudes

Brian Bond, Omar Espinoza, and Philip Araman

Abstract

Lumber is usually dried to a specific moisture content prior to further 

manufacturing or use. While lumber can be air-dried, the ambient humidity 

in most localities prevents the lumber from reaching the moisture content 

necessary for dimensional stability and use, especially for interior use. 

Solar kilns are an inexpensive alternative to conventional steam-heated 

kilns, especially for small operations and communities. Solar-heated kilns 

have great potential in developing countries, especially in remote locations 

with little access to conventional energy sources. This publication describes 

the construction and operation of a solar kiln for lumber drying in tropical 

latitudes.

Keywords: Kiln drying, low-cost lumber drying, lumber drying, solarheated lumber drying, tropical hardwoods, tropical wood drying.

INTRODUCTION

Lumber is usually dried to a specific moisture content (MC) 

prior to further manufacturing or use because wood changes 

its dimensions with changes in MC. The amount of water 

in wood is usually expressed as moisture content and can 

be directly measured or calculated. The MC of wood is 

defined as the ratio of the weight of water in wood to the 

dry weight of the wood material.1 While lumber can be airdried, the ambient humidity in most localities prevents the 

lumber from reaching the MC necessary for the dimensional 

stability, especially for interior use. Furthermore, wood is 

prone to biological deterioration at higher moisture contents. 

Solar kilns are an inexpensive alternative to conventional 

steam-heated kilns, especially for small operations, like 

wood crafts makers. Solar-heated kilns have great potential 

in developing countries, especially in remote locations with 

little access to conventional energy sources. This publication 

describes the construction and operation of a solar kiln for 

lumber drying in tropical latitudes. 

OVERVIEW OF SOLAR KILN DESIGN 

The solar kiln described in this publication was designed, 

constructed, and tested at Virginia Polytechnic Institute and 

State University (Virginia Tech) in Blacksburg, VA. This 

design is based on 25 years of research and development 

on solar drying of lumber in the United States and foreign 

countries. Previous versions of this kiln were designed to 

1

 According to the equation: MC = [(Weight of water in wood) / (Weight of 

oven-dried wood)] x 100 percent.

Design and Operation of a Solar-Heated 

Dry Kiln for Tropical Latitudes

Brian Bond, Omar Espinoza, and Philip Araman

hold up to 2,000 board feet (4.7 m3) of lumber.2 The version 

described here can hold between 500 and 800 board feet 

(1.2 to 1.9 m3) of lumber and allows drying in conditions 

common in tropical countries. The pictures shown here 

were taken during the construction of the kiln at Virginia 

Tech, and depict some differences in design from the 

drawings (see appendix A), most importantly: (1) the roof 

angle shown in the pictures is 45 degrees, appropriate for 

Virginia’s latitudes, while that of the roof shown in the 

drawings is 17 degrees; (2) doors are located in the wall 

opposing the equator in the kiln built at Virginia Tech, while 

the drawings show doors on the equator-facing wall (north 

face in southern latitudes). 

While there are several different types of solar kilns for 

drying lumber, the kiln described here was designed with 

two major objectives: (1) inexpensive construction, and (2) 

simple operation. Drying lumber can be a complex process 

of attempting to accelerate drying while maintaining the 

quality of the lumber, and therefore, the process often 

requires extensive knowledge and experience. The kiln 

design explained here has the advantage of requiring 

no extensive knowledge, experience, or control in its 

construction and operation. The size of the collector keeps 

the kiln from overheating, thus minimizing checks and 

splits. The kiln is simple to construct and utilizes a passive 

solar collector, four insulated walls, and an insulated floor. 

The roof is made of clear, greenhouse-rated, corrugated 

polycarbonate. 

SOLAR KILN DESIGN FUNDAMENTALS

The solar kiln can hold up to 800 board feet (1.9 m3) of 

1-inch (25.4 mm)-thick lumber per load, and can dry a 

charge in approximately 1 month of moderately sunny 

weather. The kiln is heated when solar energy enters the 

clear glazing and is absorbed by the black-painted interior 

surfaces. The solar energy heats the air in the collector 

space and is circulated through the lumber by fans. As the 

heated air circulates, it absorbs moisture from the surface of 

the lumber. The evaporated moisture increases the relative 

humidity of the air, and when the humidity in the chamber 

becomes too high, it can be vented from the chamber 

through the vents in the rear of the kiln. These vents also 

allow for fresh, dry air to enter the kiln.

2

 One board foot is a volume unit for lumber, equivalent to a piece of 

wood with dimensions 12 x 12 x 1 inch. A cubic meter of lumber contains 

approximately 424 board feet. To calculate the total number of board feet 

in a board, use the following equation: Board feet of lumber (BF) = length 

(feet) x width (inches) x thickness (inches) / 12.
Roof Design

The kiln design is similar to a solar greenhouse. A passive 

solar collector provides the kiln’s drying heat, which is 

generated from the sunlight that passes through the glazed 

roof and strikes a solar collector inside the kiln. Many 

factors affect how much heat can be obtained from the 

sunlight. One is the slope of the roof, which in this design 

is 17 degrees to the north, measured from the horizontal, 

assuming a location in the southern hemisphere. The 

optimum roof angle is dependent on the kiln location and is 

optimally equal to the latitude. One difficulty in choosing 

the optimal roof angle is that the optimal angle for solar 

collection changes with the season because the angle of 

the sun with respect to the horizontal changes. If you are 

planning on operating the kiln during the winter months, 

you can improve your collector’s performance by increasing 

the roof angle another 10 degrees. Very importantly, all 

references to the roof angle and walls orientation in this 

publication assume a location in the southern latitudes; if the 

kiln is located north of the equator, this should be considered 

in making the necessary changes (e.g., roof would face the 

south). Table 1 lists the latitudes of some cities in South 

America.

The type of transparent roofing material, or glazing, can also 

affect the amount of heat energy collected from the sun. The 

glazing must transmit sunlight through to the solar collector 

and not reflect it. It must also have some protection from 

degradation by the sun’s ultraviolet rays. Many different 

glazing materials are possible, including glass, polymer 

plastic films, and fiberglass panels (see the References 

section for information on the different types of glazing). 

The kiln built at Virginia Tech uses a greenhouse-rated 

corrugated polycarbonate. For winter operation or in cooler 

climates, it is best to use two layers of clear glazing; these 

layers are separated by 1.75 inch (90 mm) rafters to help 

insulate the solar collection area (fig. 1). The roof is framed 

with widely spaced rafters that must accommodate the width 

of the covering material and any anticipated snow loads. 

The most critical design feature of this solar kiln is that there 

is 1 square foot of collector for each 10 board feet of 1-inchthick lumber in the dryer (or 4 m2

 for each m3 of lumber). 

This ratio provides an appropriate amount of heat for oak 

(Quercus sp.) 1-inch (25.4 mm) thick, but may provide too 

much heat for oak 2 inches (50.8 mm) thick or thicker; and 

too little for pine or other fast-drying woods. Oak is one of 

the more difficult drying woods because if it is dried too 

rapidly, it will crack and check, and if dried too slowly, the 

sapwood may stain and discolor. In general, thicker lumber 

should be dried more slowly than thinner lumber. As an 

example, 2-inch (50.8 mm)-thick lumber that is 2 inches 

(50.8 mm) thick will take approximately 2 1⁄2 times longer 

to dry than lumber of the same species that is 1 inch (25.4 

mm) thick. The collector area can be increased to provide 

more heat for easier drying woods than oak by extending the 

roof and/or reducing the height of the north wall, or simply 

loading less material in the kiln. These changes increase the 

collector area-to-board foot ratio. An easy way to provide 

less heat is to reduce the collector area simply by covering 

part of the roof with plywood or other opaque material.

Basic Box Design

The kiln can be built with concrete blocks, brick and mortar, 

or other materials. The kiln described here is constructed 

using standard framing techniques (fig. 2). The first step 

is to construct the floor with 2- by 7-inch (40 by 170 mm) 

joists. The lumber used for the floor should be preservative 

treated to prevent rot because it will be close to, or in 

contact with, the ground. Next, install insulation material 

between the framing members (table 2). Cover the top of 

the fiberglass insulation with a sheet of 0.6 Mil plastic to 

prevent condensation from entering the insulation material. 

Finish the floor by placing exterior grade 3/8-inch (9.5mm) 

plywood across the joists. Next, construct the walls of the 

kiln using 2- by 4-inch (40 by 90 mm) studs, insulation 

material, and exterior grade 3/8-inch (9.5 mm) plywood on 

both the interior and exterior of the frame. The plywood 

inside the kiln is painted with two coats of black rubberbased concrete sealer, which when dry, acts as a vapor 

barrier and black solar collector. Another option would be to 

paint two coats of aluminum paint for vapor barrier and then 

a third coat of black paint to absorb the solar energy. Some 

examples of sealers are shown in figure 3.

Table 1Ñ Latitudes of some South American 

cities

City Ð country Latitude

Santa Cruz Ð Bolivia 17d 46m S

Lima Ð Peru 12d 0m S

Bogota Ð Colombia 4d 32m N

Quito Ð Ecuador 2d 10m S

Figure 1—Painted interior, showing layer of glazing.

2
The exterior of the kiln is painted with an exterior-grade 

paint to prevent weathering. Be careful not to use a vapor 

barrier like aluminum paint on the exterior, since any 

moisture that might migrate into the walls will not be able to 

escape to the outside.

The current design has large doors at the front of the 

structure for loading, unloading, and monitoring kiln 

samples. The example kiln at Virginia Tech has these 

access doors at the rear of the kiln, as shown in figure 4. 

Two access doors at each end (east and west walls) can be 

installed to permit the periodic examination of the lumber 

and measurement of moisture content. Another possible 

modification is a roof hinged to the south wall and the north 

wall hinged to the floor (again assuming a kiln built for 

the southern latitudes). This permits the roof to be raised 

and north wall lowered to facilitate loading and unloading. 

Regardless of the design, vents should be added to the south 

wall. The vents can be as simple as framed openings with a 

small piece of plywood to cover the vent when not needed, 

or you can purchase a commercial vent similar to those used 

for basement and crawlspace ventilation. 

The three fans used in this design are inexpensive, threespeed window fans with plastic blades (fig. 5). The fans 

are fastened to the roof framing about 20 inches (0.50 m) 

in front of the south wall with a plywood shroud or baffle 

around them extending downward 36 inches (0.90 m) below 

the roof and running the full length of the dryer in order to 

force the air through the lumber pile (fig. 6). Whenever the 

kiln is left empty, be careful that you do not leave the doors 

completely closed because the temperature of an empty kiln 

can exceed 200  ̊F (90  ̊C), which can damage the plastic fan 

blades.

OPERATION OF A SOLAR DRYER

Preparing the Lumber

Green lumber should be end coated with a rubber based 

basement sealer or other commercial end coating product 

immediately after sawing to prevent large losses from end 

Figure 2—Interior framing.

Table 2—Thermal resistance of some construction and

insulation materials 

Materials Thickness RSIa

 value

inches – mm m2 x C°/W 

Glass fiber 1 - 25 0.55 

Expanded poliestirene 1 – 25 0.65 

Wood shavings 1 – 25 0.42 

Air space 1 – 25 0.18 

Pine wood 1.75 – 90 0.78 

Concreteb 4 - 100 0.13 

Concrete block 4 – 100 0.12 

12 – 300 0.22 

Common brick 4 – 100 0.07 

a RSI = Resistance to heat flow. The value of RSI increases 

proportionally with the material thickness.

b

 Density = 110 lb./ft3 (1,760 kg/m3

).

Figure 3—Coatings that can be used to seal the inside walls of the kiln 

and to coat the ends of sample boards. From left to right: aluminum roof 

coating, a commercial kiln coating, and rubberized roofing sealer.

Figure 4—A solar kiln in the United States with rear doors. The drawings 

at the end of this publication depict a design that incorporates the doors at 

the front end of the kiln.

3
checks and splits. End coating is ineffective when applied 

after the lumber has begun to dry. Lumber should then be 

stacked in the kiln with a 12-inch (0.30 m) clearance on 

either side of the stack (between the north and south walls 

and the stack) to permit adequate air circulation, and in wellconstructed layers, separated by stickers or spacers running 

perpendicular to the lumber’s length (fig. 6). Lumber in each 

layer must be uniform in thickness. If the sawn lumber is 

variable in thickness, one or both faces of the boards should 

be planed before drying to obtain a uniform thickness and 

reduce warping during drying. Green lumber should be 

stacked with stickers quickly after sawing or it may begin to 

stain, particularly in the warmer months.

Stickers used between each layer of wood are typically 

of 0.75 to 1 inch (19 to 25 mm) in thickness and 1 to 1.25 

inches (25 to 32 mm) in width; and the length should 

be equal or slightly longer than the pile’s width. It is 

important that stickers are uniform in thickness and kept 

dry. Stickers are placed perpendicular to the boards’ length, 

every 12 to 18 inches (0.30 to 0.46 m) along the lumber’s 

length, using narrower spacing for warp-prone species. The 

stickers should be placed directly above the stickers in the 

lower layers, in straight columns. If the lumber is of varying 

lengths, shorter boards are staggered by alternating them 

from one end to the other of the pile with the longest pieces 

always on the outside edges. The ends of every board should 

be supported with a sticker. The stickers hold the lumber 

flat, preventing warp, while allowing air to circulate through 

the pile and dry the lumber.

While the lumber is being stacked or prior to loading the kiln 

with pre-stacked lumber, several sample boards must be cut 

(see the section on Procedures for Cutting and Using Sample 

Boards). Periodically checking these samples will allow you 

to determine the moisture content of the lumber in the kiln and 

identify possible drying defects. After the lumber is stacked in 

the kiln, lay a final layer of stickers down and then a blackpainted sheet of plywood to act as a cover and collector.

Monitoring the Process

Monitoring the MC during the drying process is important 

to avoid drying too rapidly, resulting in quality loss, and to 

know when the load has reached the desired MC. Sample 

boards are used to measure the MC each day and determine 

the daily rate of moisture loss. This loss should be compared 

with the safe drying rate for that species. If the drying rate 

is too fast, then it may be necessary to block off part of the 

collector, or else turn the fans off and open the vents during 

the hottest part of the day.

While the solar kiln described in this publication is designed 

to dry red oak without checking, you still want to monitor 

the drying process. Monitoring the moisture loss and quality 

of the wood during the drying process will help you to 

maximize the efficiency of the solar kiln. Lumber should 

be dried to the maximum safe drying rate. The safe drying 

rate refers to the moisture loss in one day, not the average 

loss over several days. Because the safe drying rate for most 

tropical species are not known, moisture losses and drying 

quality should be monitored daily and the process adjusted 

as necessary. Table 3 lists the safe drying rate for common 

North American hardwoods. Softwoods are typically able to 

dry at a much faster rate and moisture content losses above 

10 percent per day are quite common.

When lumber has its highest MC (green lumber), it is most 

important to adhere to the safe drying rate. It is during the 

first one-third moisture content loss that most checking and 

splitting occurs. Once the lumber dries below 22 percent 

MC, the risk of creating new cracks and splits is low. The 

final MC should be as close as possible to the prevailing 

equilibrium moisture content (EMC) of the service 

conditions. This will limit the amount of dimensional 

changes that would occur when the wood is processed and 

Figure 5—Front view of kiln showing fan placement.

Box Fan

Airflow

Baffle

Solar

Collector

Lumber

Figure 6—Diagram of solar kiln showing fans, baffle, solar collector, and 

spacing between lumber and walls.

4
in service. As an example, table 4 lists the average outdoors 

EMC values for three locations in Bolivia.

If lumber is drying too rapidly, there are several ways to 

reduce the drying rate. The best method is to cover up part 

of the collector. Shutting the fans off will also reduce the 

drying rate but may result in temperatures high enough to 

melt the plastic fan blades.

It is impractical to weigh every board in the dryer to 

measure the moisture loss rate, and electric meters are 

not accurate above 30 percent MC. Use the sample board 

method to determine the MC of lumber in the kiln. This 

method uses short, carefully chosen sample boards sawn 

from larger pieces of lumber, and these sample boards are 

weighed periodically and estimated moisture contents are 

calculated. Since the wettest or slowest drying lumber in the 

kiln has the highest risk of splitting and cracking, the sample 

boards should represent this kind of lumber. Typically, 

samples should be cut from the most recently cut wood, the 

widest and thickest boards, lumber with the most heartwood, 

and boards that are quarter sawn.

The temperature inside the kiln will increase during the day 

until it peaks at mid afternoon and then cools at night. At 

night, as the air in the kiln cools, the relative humidity will 

increase significantly. The increase in humidity at night is 

beneficial in reducing or relieving the drying stresses that 

developed during the day. Fans should be turned off at night 

to allow the lumber to relieve stress.

There are two simple controls that can make operating 

your solar kiln easier. A simple timer can control the fan 

operation. The timer can be set to come on at mid morning 

as the temperature in the kiln increases and to shut the fans 

off in the evening as the temperatures cool. A humidistat can 

be used to override the timer for the fans. The humidistat 

is used to keep the fans off during days when it is raining, 

causing high humidity, which is detrimental to the drying 

process.

Modifying the Design to Control Operation

As mentioned in the Roof Design section, the angle of the 

roof with the horizontal should be equal to the latitude of the 

location where the kiln is going to operate; thus, the most 

important adaptation is to give the roof the proper angle by 

lowering and/or raising the walls of the kiln. The collector 

area-to-lumber footage ratio should be maintained to 

approximately 1 square foot of collector for every 10 board 

feet of lumber.

One potential modification recommended for tropical 

countries is to make a clear north wall. This is not 

incorporated in the design presented here because there is a 

significant tradeoff between the area of the collector and the 

area of insulated, solid walls. The larger the collector size, 

the more solar energy is collected, however, the greater the 

heat loss in colder weather. In the present design, to make 

this change it is also necessary to move the doors to the wall 

facing south.

If you want to make your solar kiln entirely powered by 

solar energy, there are several options available. The two 

most common are to: (1) use a photovoltaic solar collector 

and a current converter to run the alternating currentpowered fans on solar energy, or (2) use a photovoltaic solar 

collector and use direct current-powered fans. However, 

both options will significantly increase the cost of building 

a solar kiln. At the time of construction of the current kiln, 

powering the three fans with solar energy increased the 

construction costs by 50 to 70 percent. For more information 

on solar powering of fans, see appendix B.

Table 3—Safe drying rates of some North American hardwoods 

Maximum rate of MC loss per day 

Species Density 

1-inch 

(25.4mm)- thick 

lumber 

2-inch 

(50.8mm)- thick 

lumber 

g/cm3 – lb/ft3 ------------ percent ------------ 

Cherry 0.53 - 33.1 5.8 2.3 

Beech 0.68 - 42.4 4.5 1.8 

Red oak upland 0.62 - 38.7 3.0 1.5 

Yellow-poplar 0.46 - 28.7 13.8 5.5 

MC = Moisture content.

Table 4—Average equilibrium moisture 

content (EMC) values in three Bolivian cities 

City EMCa

percent 

Cochabamba 9.7 

La Paz 9.3 

Santa Cruz 12.6 

a Calculated using historic temperature and relative 

humidity data from the Bolivian weather service.

5
PROCEDURES FOR CUTTING 

AND USING SAMPLE BOARDS

1. Select a few boards from the pack of lumber that 

represent the slowest drying material. Theses boards 

would be the widest and thickest and would have 

the highest MC. They also would contain the most 

heartwood or would be quarter-sawn.

2. Cut a 24- to 30-inch (0.60 to 0.76 m) sample that is free of 

knots and at least 12 inches (0.30 m) from the end of the 

board. Then cut two 1-inch (25 mm) moisture sections from 

the sample board’s ends, as shown in figure 7. Make sure to 

number the two moisture sections and the sample board.

3. Immediately weigh the 1-inch (25 mm) sections within an 

accuracy of 1 g and record the weight. Measure weight 

rapidly after cutting because it is important that the sections 

do not lose moisture. Do not end-coat these sections.

4. Place the 1-inch (25 mm) sections in an oven at 215.6 oF

(102 oC) and dry them for 24 hours. Reweigh them to 

obtain the oven dry weight.

5. Using equation 1, calculate the MC of each section and 

average the MC of the two sections to obtain the initial 

MC of the sample board.

MC(%)= -1 X 100% Weight of wet section

Weight of oven dried section [1]

6. End-coat the sample board with a rubber-based sealing 

compound or two coats of aluminum paint (fig. 8). Then 

weigh the sample board and record weight on sample (within 

5 g accuracy). This is the weight of the wet sample board.

7. Using equation 2, estimate the oven-dry weight of the 

sample board using the average MC calculated in step 5 

and the weight of the wet sample from step 6. Record this 

so it can be used for future moisture content calculations.

[2] Estimated oven

dry weight (g)

Weight of wet sample board

100+MC% =

8. Place the sample board in the lumber stack in a location 

where it will dry at the same rate as the rest of the 

lumber in the dryer (fig. 9).

9. To determine the MC at any time, reweigh the sample 

board and calculate MC using equation 3. Figure 10 

shows an example of how MC can be recorded.

Current MC(%)= -1 X 100% Current weight of sample board

Estimated oven dry weight [3]

10. Stop the drying process when the current MC (percent) 

equals your target MC.

Figure 9—Pack of lumber with sample boards.

Figure 8—Sample boards with different end coatings.

End of

Lumber

over 1’ 2’6

1” 1”

Figure 7—Dimensions and picture of sample board for controlling the 

drying process.

6
ACKNOWLEDGMENTS

Special thanks to those who assisted with the design and 

construction of the solar kiln: Rick Caudill, Kenny Albert, 

and Fred Albert. Some information for this publication was 

adapted from: Wengert, E.M. Solar Heated Lumber Dryer 

for the Small Business. MT # 20 Utilization and Marketing. 

Virginia Polytechnic Institute and State University, Virginia 

Cooperative Extension Service. Blacksburg, VA. April, 1980.

REFERENCES

Glazing Materials

Different types of greenhouse coverings. www.igcusa.com/TECHNICAL/

Coverings.html. [Date accessed: April 30, 2010].

Giacomelli, G.A. Greenhouse glazings: WhatÕ s new under the sun, under the 

glazing, and at the plant canopy. In: Southeastern United States Greenhouse 

Vegetable Growers Conference and Trade Show Proceedings. 

Lumber Drying

These publications can be downloaded from www.fpl.fs.fed.us:

Simpson, W.T., ed. 1991. Dry Kiln OperatorÕ s Manual. United States 

Department of Agriculture Forest Service. Forest Products Laboratory. 

Agric. Handb. 188. Madison, WI: U.S. Department of Agriculture Forest 

Service, Forest Products Laboratory. 274 p.

Denig, J.; Wengert, E.M.; Simpson, W.T. 2000. Drying hardwood lumber. 

Gen. Tech. Rep. FPL-GTR-118. Madison, WI: United States Department of 

Agriculture Forest Service. Forest Products Laboratory. 138 p. 

Forest Products Laboratory. Air drying of lumber. Gen. Tech. Rep. FPLGTR-117. Madison, WI: United States Department of Agriculture Forest 

Service. Forest Products Laboratory. 62 p.

Figure 10—Sample of recordkeeping sheet for sample board data.

Wet weight (g) OD weight (g) 1 2 3 4 .....

Weight

MC

Weight

MC

Weight

MC

Sample boards

Day

2

n

Sample number Moisture sections

1

Green weight 

(g)

Estimated OD 

weight (g)

7
APPENDIx A

Design drawings for the solar kiln 

8
Appendix A (Continued)

9
Appendix A (Continued)

10
Appendix A (Continued)

11
Appendix A (Continued)

12
Appendix A (Continued)

13
APPENDIx B

Solar Powered Fans

Creative Energy Technologies Inc

2872 State Rte 10

Summit, NY 12175

Green Home: Environmental Store

850 24th Ave.

San Francisco, CA 94121

Fax: 415-752-6389

14
Bond, Brian; Espinoza, Omar; Araman, Philip. 2011. Design and operation of a solarheated dry kiln for tropical latitudes. Gen. Tech. Rep. SRS-134. Asheville, NC: U.S. 

Department of Agriculture, Forest Service, Southern Research Station, 14 p.

Lumber is usually dried to a specific moisture content prior to further manufacturing or 

use. While lumber can be air-dried, the ambient humidity in most localities prevents the 

lumber from reaching the moisture content necessary for dimensional stability and use, 

especially for interior use. Solar kilns are an inexpensive alternative to conventional 

steam-heated kilns, especially for small operations, and communities. Solar-heated kilns 

have great potential in developing countries, especially in remote locations with little 

access to conventional energy sources. This publication describes the construction and 

operation of a solar kiln for lumber drying in tropical latitudes.

Keywords: Kiln drying, low-cost lumber drying, lumber drying, solar-heated lumber 

drying, tropical hardwoods, tropical wood drying.
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of Agriculture (USDA), is dedicated to the 

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CongressÑt o provide increasingly greater service to a 

growing Nation.

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