Operation and Cost of a 

Small Dehumidification 

Dry Kiln 

Richard D. Bergman

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Note

FPL–RN–0310
October 2008

Bergman, Richard D. 2008. Operation and Cost of a Small Dehumidification Dry Kiln. Research Note FPL-RN-0310. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 20 p.

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Abstract 

Obtaining small quantities of custom kiln-dried lumber 

can be an expensive process for an individual woodworker. 

Building and operating a small kiln capable of drying 

custom cuts of lumber (such as slabs, bowl blanks) gives 

woodworkers another option. Our approach was to build 

and operate a small dehumidification dry kiln. The four 

charges of lumber ranged from 600 to 700 board feet (bf), 

and a woodworker with no dry-kiln experience operated 

the kiln. The first charge of mixed air-dried 4/4 hardwoods 

and softwoods was kiln-dried from 18.4% to 7.3% moisture 

content (MC) in 15 days with no casehardening. The second 

charge of 5/4 black cherry lumber was kiln-dried from 

47.5% to 6.8% MC in 27 days with no casehardening, and 

the third charge of 4/4 northern red oak lumber was kilndried from 82.9% to 6.1% MC in 45 days and to 5.2% MC 

in 50 days with severe casehardening relieved by conditioning. A fourth charge of 300 bf 4/4 northern red oak, 200 bf 

of 4/4 shagbark hickory, and 100 bf of mixed 4/4 box elder 

and 4/4 black cherry was kiln-dried from 69.7% to 8.5% 

MC in 29 days with casehardening only in the northern 

red oak, and that was relieved by conditioning. We found 

that greater control of the dehumidifier operation earlier 

in the kiln schedule to maintain the safe drying rate would 

decrease the severity of casehardening when drying green 

northern red oak. New building materials, which are most of 

the initial cost, could be replaced by reused lumber. Drying 

small amounts of lumber using a dehumidification kiln is a 

suitable option for woodworkers even with limited knowledge of kilns.

Keywords: dehumidification, dry kiln, small, MATC, 

drying, operation, DH, cost

Acknowledgments 

I thank Patrick Molzhan, Program Director, Wood Technics 

Department, Madison Area Technical College; Terry Mace, 

Forest Utilization and Marketing Specialist, Wisconsin 

Department of Natural Resources; Scott Bowe, Associate 

Professor and Wood Products Specialist, University of 

Wisconsin-Madison; and Jim Gilbertson and Tedd 

Mianowski (retired), Technicians, U.S. Forest Service, 

Forest Products Laboratory.

Conversion Table 

To convert from To Multiply by 

feet per minute (ft/min) meters per seconds 0.00508 

horsepower (hp) kilowatts (kW) 0.746 

pounds (lb) kilograms (kg) 0.454 

pints (pt) liters (L) 0.473 

feet (ft) meters (m) 0.305 

feet squared (ft2

) meters squared (m2) 0.0929 

feet cubed (ft3) meters cubed (m3) 0.0283 

gallons (gal) liters (L) 3.78 

miles (m) kilometers (km) 1.61 

tons (t) tonne (×103

 kg) 0.907 

board feet (bf) meters cubed (m3

) 0.00236 

british thermal units (Btu) megajoules (MJ) 0.001055 

Contents

Page 

Introduction...........................................................................1

Methodology.........................................................................3

 Material.............................................................................3

Experimental Procedure........................................................3

Results...................................................................................5

 Kiln Data...........................................................................5

 Economic Analyses...........................................................7

Discussion.............................................................................8

Recommendations.................................................................9

References.............................................................................9

Appendix A—Bill of Materials...........................................11

Appendix B—Procedure for Cutting and Using Kiln 

Samples...............................................................................12

Appendix C—Drying Schedules.........................................13
Operation and Cost of a Small 

Dehumidification Dry Kiln 

Richard D. Bergman, Research Chemical Engineer

Forest Products Laboratory, Madison, Wisconsin

Introduction 

In the past, custom woodworkers would simply visit a local 

sawmill or lumber retail store to buy lumber, especially kilndried material, for their projects. This material might not 

be exactly what they needed and cost twice the wholesale 

price (personal communication on September 8, 2006, with 

Terry Mace, Forest Products Utilization and Management 

Specialist, Wisconsin Department of Natural Resources, 

Division of Forestry, Madison, Wisconsin). Using a custom 

lumber-drying facility to dry green lumber sawn for use by 

the woodworker could be expensive. Some woodworkers 

simply stock up on green lumber and air dry their own material. Individual woodworkers would like other options to 

help lower the cost of kiln-dried cuts of lumber.

Kiln-drying lumber is an expensive process; therefore, 

kiln-dried lumber is sold at a significantly higher price than 

green lumber. Prices from Hardwood Review Weekly (August 11, 2006) for both green and kiln-dried (gross tally) 

4/4 #2 common red oak in the North Central Region are 

505 and 750 dollars per thousand board feet, respectively. 

For 5/4 Select & Better black cherry, these prices are 2,520 

and 3,400 U.S. dollars per thousand board feet, respectively. 

The major reason for the difference in price is the cost of 

energy required to kiln-dry green lumber to a lower moisture content (MC) prior to final manufacturing. Typical MC 

range for kiln-dried lumber is 6% to 8% for interior use in 

the United States to maintain dimensional stability (FPL 

1999). Most kiln-drying of lumber is done by conventional 

steam kilns, which can be energy-intensive operations. For 

a conventional steam dry kiln, the approximate amount of 

energy to kiln-dry a thousand board feet of Douglas-fir, 

Southern Pine, and northern red oak green lumber is 1.2, 

3.0, and 6.5 million Btu, respectively (Comstock 1975). 

Large commercial dry-kiln facilities produce most of the 

available kiln-dried lumber at a significantly lower cost per 

unit than other methods. A typical large dry-kiln operation 

uses steam coils as the indirect heating source fueled either 

by burning woody biomass, fossil fuels, or both. The size 

and type of dry kilns needed for these operations has limited the ability for small operators to enter the commodity 

market or produce kiln-dried lumber for their own use at a 

competitive price. However, some small dehumidification 

(DH) dry kilns under 3 horsepower have been commercially 

available since 1976. One company, Nyle Corporation 

(Bangor, Maine), has already sold 5,000 DH units intended 

for 2,000 to 5,000 board feet. More than 7,000 DH units 

under 10 horsepower are in use along with many large ones 

(personal communication on October 10, 2006, with E.M. 

Wengert, Professor Emeritus in Wood Processing, Department of Forest Products, Virginia Tech University). One 

problem is that most commercially dried lumber is in standard thicknesses and lengths that may not meet an individual woodworker’s needs. In the United States, woodworkers 

have expressed interest in producing their own kiln-dried 

lumber from less expensive green lumber to maintain greater control throughout the manufacturing process. Sometimes 

specialty lumber is required, but buying the material commercially or using a custom kiln-drying operation can be 

cost-prohibitive.

Technology has advanced not only in understanding the process of wood drying on small scales (less than a thousand 

board feet) but also in commercially available products used 

to build these small dry kilns capable of producing highquality lumber. Types of dry kilns capable of commercial 

operation include solar, vacuum (radio-frequency, heated 

platens, or super-heated steam), microwave, and dehumidification. All these systems have their advantages and disadvantages. For example, solar dry kilns perform better in 

areas with higher solar radiation, whereas radio-frequency 

vacuum kilns have high initial capital costs and require a 

highly trained operator. 

Research on drying small quantities of lumber began decades ago at the Forest Products Laboratory (FPL) with a 

significant focus on solar kilns (Peck 1961; Simpson and 

Tschernitz 1984; Simpson and Tschernitz 1988; Tschernitz 

and Simpson 1985). For the remote locations designed for 

solar drying, DH kilns were not as applicable as solar kilns 

because inexpensive and stable grid-quality electricity was 

not available. Recent research also showed the potential for 

solar drying on a small scale in southern climates (Bond 

2006). However, in northern climates such as the northern 

United States, DH kilns have the advantage of running multiple charges during the year, whereas solar kilns are often 

limited to one charge during the winter because of limited 

solar radiation. Also, unless a solar kiln has photovoltaic 

power to the fans, both systems still require electricity. Other research included combining solar and dehumidification 

capabilities into one kiln, which increased energy efficiency 

by 30% (Chen and Helmer 1987). 
Research Note FPL–RN–0310

2

Dehumidification dry kilns are not as significantly affected 

by outside environments as are solar kilns because air exchange is not needed to remove moisture-laden air. Instead 

of using steam coils and vents for moisture removal from 

the lumber and the dry kiln as is done in commercial dry 

kilns, the dehumidifier uses electricity to cool the air enough 

to condense the moisture released by the lumber. This condensation action keeps the heat of evaporation in the kiln. 

This heat is usually lost in kilns using vents for wet-bulb 

control. The fans circulate air through the lumber stack and 

as the warm, moist air leaving the stack contacts the cooling 

coils of the dehumidifier, the moisture is condensed (Fig. 1). 

For commercial operations, waste heat from the fans and 

dehumidifier keeps the drying chamber at the required 

temperature once the kiln reaches operating temperature 

(Fig. 2). 

For smaller DH kilns, a commercial stand-alone dehumidifier is placed in the kiln (drying chamber). This dehumidifier 

works likes an air conditioner except the dehumidifier has 

both its hot and cold coils in one unit. A fan draws the warm 

moist air into the unit and the moisture condenses on the 

cold coils that are similar to an air conditioner’s evaporator coils. The condensation drips through a hose to a drain 

or into a removable bucket (Fig. 3). The second set of coils 

warms the cool dry air, and the warm, dry (reconditioned) 

air is pumped into the kiln to absorb more moisture from the 

lumber. Some residential dehumidifiers have digital controls 

for setting the relative humidity, whereas other dehumidifiers can be controlled by a humidistat that allows dehumidifiers to cycle on and off to maintain a wider range of relative 

humidity (RH) than is possible by standard controls. The 

amount of condensate can be used to track the drying rate 

to adjust the RH setting for an optimal drying rate. Optimal 

drying rate is dependent on the species, initial moisture content, wood temperature, air speed, and lumber thickness. 

This project was a collaboration between the Wisconsin Department of Natural Resources and Madison Area Technical 

College (MATC) to construct a 600-bf dehumidification dry 

kiln based on plans from an article (AW 2002) for drying 

small quantities of lumber. The main objective was testing 

the versatility and functionality of drying several domestic 

wood species at different moisture contents using a woodworker with no previous dry-kiln operational experience. 

Figure 1—Typical dehumidification kiln (FPL 1999 

p. 12–10).

Figure 2—Typical dehumidification cycle (FPL 1999 p. 

12–10).

Figure 3—Residential dehumidifier.
Operation and Cost of a Small Dehumidification Dry Kiln

3

Methodology

Material

The Madison Area Technical College (MATC) Wood Technics Department (WTD) bought the material listed in Appendix A using a grant through the Wisconsin Department 

of Natural Resources. Personnel from MATC WTD built 

the 600-bf dehumidification dry kiln based on 2-in. by 6-in. 

residential housing practices. See Bowe and others (2007) 

for greater construction detail on building this kiln (Fig. 4).

All the kiln components were commercially available. 

A Maytag 30-pint residential model dehumidifier (Whirlpool Corporation, Benton Harbor, Michigan) using standard 

115-volt power was installed for dehumidification; maximum dehumidifier power consumption was 0.851 kilowatts 

(kW). Suggested dehumidifier compressor sizing was 

1 horsepower per 1,000 board feet of mixed hardwoods 

(Wengert and others 1988). This dehumidifier could be digitally set from a maximum of 90% to a low of 35% relative 

humidity (RH), and the setting was used to change the drying rate. Also, the installed circulating fans operated only in 

one direction as only one typical-size pack of lumber was 

loaded in the kiln (Fig. 5). Commercial dry kilns reverse 

fan direction to even the drying rate for the large number of 

packs. Supplemental heat was from an electric baseboard 

heater capable of generating roughly 800 (75%) or 1,150 

(100%) watts depending on its setting. This heater was used 

later in the drying cycle if needed or could be used when 

the kiln operated outside during cold weather to maintain 

kiln temperatures above 65°F. Most dehumidifiers perform 

poorly under 65°F and the risk of freezing the coils also 

increases. Top baffling was constructed from 1/2-in. CDX 

sheathing (C-D Exposure 1 plywood) and could be raised 

while loading and unloading the kiln. This baffling forced 

the circulating air through the pack, and the lumber was 

stacked to prevent side air flow past the pack. The circulating fans were also installed into the 2-in. by 4-in. framework 

as shown in Figure 6. Air flow readings of 25 and 200 ft/min 

were measured at bottom and top of charge, respectively, 

using an Alnor Velometer hand-held aerometer (Alnor 

Products, Shoreview, Minnesota). Two more fans were installed after Run 2 to both increase fan speed to roughly 

400 ft/min and evenly distribute the air flow. Both sets of 

fans can be operated independently. Metal components not 

made of stainless steel were used to save money and were 

evaluated on their corrosion resistance after the four runs 

were complete. 

Experimental Procedure

After construction was completed, the dry kiln was loaded 

with a local supply of air-dried 4/4 hardwood and softwood 

species including red pine, bur (white) oak, black cherry, 

and shagbark hickory. All kiln operations were run by 

MATC personnel with oversight by FPL personnel. All four 

dry-kiln runs were done inside a temperature- and humiditycontrolled building, although the kiln can be used outside. 

Run 1 was conducted to verify proper operation of the new 

DH kiln using air-dried lumber. Air-dried lumber has a minimal chance of casehardening during kiln-drying compared 

with green lumber (Denig and others 2000). 

After Run #1 was complete and the dry-kiln operation verified, the dry kiln was unloaded and reloaded with 5/4 green 

black cherry (Prunus serotina) lumber sawn from a local 

portable chainsaw mill operation. The black cherry lumber 

was transported in a truck in two trips for a total kiln capacity of 640 bf for Run 2. After kiln-drying the black cherry, 

the kiln was unloaded. Prior to reloading, two fans were 

added to the fan deck to increase air flow and uniformity 

and then the kiln was reloaded with 4/4 green northern red 

oak (Quercus rubra) lumber sawn from a local sawmill. The 

Figure 4—Front view of the dehumidification dry kiln 

(empty) with main doors on the side.

Figure 5—Side view of dry kiln indicating air 

direction and location of major components. DH 

is dehumidification.
4

Research Note FPL–RN–0310

northern red oak lumber was transported in two trucks for 

a total of 600 bf for Run 3. The dry kiln was unloaded and 

reloaded with 300 bf of 4/4 northern red oak, 200 bf of 4/4 

shagbark hickory (Carya ovata), and 100 bf of mixed 4/4 

black cherry and box elder (Acer negundo) lumber sawn 

from a local sawmill. This lumber was sawn from logs endcoated and stored for 5 weeks prior to sawing. The lumber 

was transported in two trucks for a total of 600 bf for 

Run 4 (Fig. 7).

Both kiln samples and condensate collected from the dehumidifier were used to monitor the MC change throughout 

the drying process. Three to four kiln samples were used per 

run and placed both at the corners roughly 1 ft from the edges and at the center of the pack. For all runs, the moisture 

loss from the kiln samples was monitored with the expectation that measurements would be taken daily. Along with 

using kiln samples to monitor lumber MC, the condensate 

was collected from the dehumidification process. A bucket 

collected the condensate, and the condensate volume was 

measured and recorded including the day and time of collection for estimating moisture loss. 

Ways to reduce the initial drying rate and casehardening for 

northern red oak were evaluated after finding severe casehardening in Run 3. The controls did not allow for a higher 

relative humidity setting; therefore, a simple lamp timer was 

installed on the dehumidifier to shorten the dehumidifier 

operating time. The dehumidifier also has its own fan that 

was set on high for black cherry and low for northern red 

oak. Lowering the fan speed on the dehumidifier, however, 

does lower its efficiency. 

Average daily moisture loss (DML) was calculated using 

Equation (1) and sample board weights for each run. 

×100 



 





 − = d

MC MC

DML DBO DBF (1)

DML is average daily moisture loss (%),

MCDBO initial moisture content of the lumber on a 

 dry basis (%),

MCDBF final moisture content of the lumber on a 

dry basis (%), and

d total number of days between measuring 

 moisture content.

Kiln samples are used for higher value wood products such 

as hardwood lumber to prevent drying defects but still maintain the maximum safe drying rate to produce the highest 

volume possible. Daily weighing of kiln samples is highly 

recommended. Figure 8 shows an example of a kiln sample 

used; detailed instruction on procedures for cutting and using sample boards are in Appendix B. Core and shell MC 

were also taken for one run to calculate the difference and 

determine if equalization of the lumber was needed. Equalization is the process of reducing the moisture between the 

core and shell of the lumber because variations in final MC 

can cause later processing problems. Figure 9 illustrates the 

proper method of cutting sections for measuring the shell 

and core MC. 

Prong tests were also performed at the completion of the 

charge to check for drying stresses. Drying stresses are 

discussed in chapter 1 of the Dry Kiln Operator’s Manual

(Simpson 1991). These test sections were cut along the 

width of the board and the interior wood was removed 

(Fig. 10a). When the sections of the board have stress, the 

two outer prongs close in because any drying stress is released by the saw cut (Fig. 10b). Only the two-prong test 

was done in this study, although a larger number of prongs 

may be used. Figure 11 highlights the extent of casehardening possible from drying. More details are available 

in chapter 6 of the Dry Kiln Operator’s Manual

(Simpson 1991).

Figure 6—Dehumidification dry kiln loaded with airdried mixed hardwood and softwood.

Figure 7—Dehumidification dry kiln loaded with green 

mixed hardwood (four fans are shown, because two 

were added).

DML

MCDBO – MCDBF
5

Operation and Cost of a Small Dehumidification Dry Kiln

For relieving casehardening found after drying, an electric 

steam kettle was used initially but it required refilling every 

half hour; therefore, a Lasko Model 1129 High Efficiency 

Circulating Humidifier (Lasko Products, Inc., West Chester, 

Pennsylvania) capable of emitting 9 gallons per day of water 

vapor was used. The amount of use depended on the severity of casehardening (Fuller and Hart 1994; Simpson 1991).

Results

Kiln Data

Run 1

The drying schedule shown in Appendix C (Table 1) was 

based on tracking condensate output from the dehumidifier. 

Changes in MC of the four kiln samples are shown in Appendix C (Table 2). Initial and final average MCDB of 18.4% 

and 7.3% were calculated for the charge of air-dried material using kiln samples, respectively. The run was completed 

in 15 days with no casehardening present during prong test; 

thus, no conditioning was required. An average daily moisture loss (DML) of 0.74% was calculated. 

Run 2

The drying schedule shown in Appendix C (Table 3) was 

based on tracking condensate output from the dehumidifier. 

Changes in MC of the three kiln samples are shown in Appendix C (Table 4). Initial and final average MCDB of 47.5% 

and 6.8% were calculated for the charge of 5/4 black cherry 

using the kiln samples, respectively. The run was complete 

in 27 days with no conditioning required because the prong 

tests showed no casehardening. Core and shell final MCDB

Figure 8—Proper method of cutting kiln samples from a full board.

Figure 9—Proper method of cutting a board into 

sections for shell and core moisture content 

(MC) (Simpson 1991, p. 125) 

Figure 10—Proper cutting for two-prong test (Simpson 

1991, p. 126).
6

Research Note FPL–RN–0310

were 8.6% and 6.8%, respectively, indicating lumber was 

properly equalized (<2% difference). 

A total of 248 pints of condensate were recorded during 

the run with an expected condensate collection of 635 pints 

based on an estimated oven-dried mass of 1,627 lb. The 

oven-dried mass for the black cherry charge was calculated 

using a green density of 45 lb/ft3 and an initial calculated 

percentage of MCDB of 47.5% for 640 actual bf of lumber 

(FPL 1995). A maximum safe drying rate of 0.0071 pints per 

hour per board foot using a dehumidifier setting of 85% was 

listed in AW (2002). This corresponded to a daily moisture 

loss of 7.0% for 4/4 black cherry lumber. This value of 7.0% 

is higher than the maximum daily moisture loss of 5.8% 

found in other literature (Denig and others 2000). In this 

study, the highest estimated daily moisture loss (DML) observed was 3.3%, although it may have been higher because 

this loss was averaged over 3 days of the highest drying period. The overall DML for the entire run was 1.5%. 

Run 3

The drying schedule shown in Appendix C (Table 5) was 

based on tracking condensate output from the dehumidifier. 

Moisture loss for the four kiln samples are shown in Appendix C (Table 6). Because a kiln operator was unavailable, 

the dehumidifier and fans were not started until 6 days after 

loading the charge. The main kiln door was open to allow 

some air-drying in the temperature- and humidity-controlled 

building. The 4/4 northern red oak lumber was kiln-dried 

from 82.9% to 6.1% MCDB in 39 days and to 5.2% MCDB in 

44 days with prong tests showing severe casehardening after 

the 44-day period. Measured air flow readings from end to 

end in the center of load were 400 lb/ft and from top to bottom were 350 to 450 lb/ft after the two fans were installed. 

Adding these two fans increased air flow by a factor of two, 

and flow was more evenly distributed. 

The kiln-dried northern red oak lumber required conditioning to remove the drying stress (Figs. 12 and 13). An electric 

steam kettle was used initially, but then the Lasko Humidifier was used instead to finish for a total conditioning time 

of 24 h between the two methods. Core and shell final 

MCDB were 5.5% and 4.4%, respectively, indicating the 

lumber was properly equalized (<2% difference). A 

Figure 11—Different levels of casehardening found after 

drying for the two-prong test (Simpson 1991, p. 126).

Figure 12— Kiln-dried northern red oak 

lumber 36 h after conditioning.

Figure 13—Conditioning completed: 

before (left) after (right).
7

Operation and Cost of a Small Dehumidification Dry Kiln

significantly larger deviation of final to initial MC existed 

for this run compared with the previous two runs. This indicates the necessity of using intermediate kiln samples to 

monitor MC for future runs of northern red oak. 

Highest DML was 4.6% compared with the maximum 

daily moisture loss of 1.0% to 3.8% found in the literature 

(Denig and others 2000) and falls outside the range of values reported by Denig and others. The DML may have been 

higher because this loss was averaged over the first 5 days 

of kiln operation (kiln samples were not measured daily). 

A basic specific gravity of 0.56 and green density of 

63.6 lb/ft3 was calculated using ASTM D2395-02, and 

specific gravity (SG) compares well with the literature 

values of 0.56 and 63 for northern red oak, respectively 

(FPL 1999). 

Run 4

The drying schedule shown in Appendix C (Table 7) was 

based on tracking condensate output from the dehumidifier. Moisture loss for the four kiln samples was shown in 

Appendix C (Table 8). The mixed 4/4 hardwoods were kilndried from 69.7% MCDB to 8.5% MCDB in 29 days, with 

prong tests showing slight casehardening initially (Fig. 14, 

left) and severe casehardening 1 month later for the northern 

red oak only (Fig. 14, right). Drying stresses occurring after 

2 days indicated a moisture content gradient that required 

equalizing, although the three kiln samples used to measure 

MC gradient between the core and shell showed less than 

2% difference. No conditioning was done until one month 

later.

Highest daily moisture loss was 5%, which is higher than 

the 1% to 3.8% found in the literature (Denig and others 

2000) and may have been even higher because the value of 

5.0% was averaged over the first 4 days of operation (kiln 

samples were not measured daily).

Economic Analyses

Electrical Consumption

Electrical consumption and costs were estimated for Runs 

2, 3, and 4 (Table 1). Run 2 had two fans operating at 100% 

for the entire run, a dehumidifier at 100% for the first 20 

days only, and 1 day each for the electrical heater at 75% 

and 100% power. Run 3 had four fans operating 100% 

for entire run and dehumidifier operating at 100% for first 

2 days and 50% for next 22 days only (no electric heat). 

Run 4 had four fans operating at 100% for the entire run 

and a dehumidifier operating at 50% for the first 18 days 

only (no electric heat).

Initial Cost

Cost for building materials was roughly $2,700 

(Appendix A), and the estimated time to build, insulate, 

paint, and wire the unit was 60 h (personal communication 

on September 3, 2006, with Patrick Molzahn, Cabinet Making and Millwork Program Director, Madison Area Technical College, Madison, Wisconsin). Assuming labor costs 

for an experienced builder, an hourly labor rate of $35.00 

was set; therefore, total cost for the installed and operational dry kiln was $4,800, including the $2,100 for labor. 

Most of the cost of the kiln was for structural material. The 

dehumidifier, fans, heater, and controls accounted for only 

about 20% of the cost. A capable woodworker could reduce 

costs greatly by purchasing used (reused) materials or using 

cheaper materials for construction.

Operational Cost

A detailed analysis of the entire costs for Run 3 included 

the purchase of 600 bf of 4/4 green #2 common red oak for 

$322.83 (including tax) directly from a local sawmill located 50 miles from MATC. Two standard trucks were used to 

transport the lumber, costing $0.50 per mile for total transportation costs of $100.00. Electrical costs were $86.72, 

with additional wood-handling costs of $200.00 assuming 

10 h of labor. Additional wood handling is associated mostly 

with loading and unloading kiln and monitoring the kiln. 

These costs were listed as operational costs because this 

work was completed by the woodworker who would use the 

kiln-dried material. A general labor cost of $20.00 per h was 

assigned for additional wood handling functions.

A typical woodworker would buy small quantities of lumber, usually less than 100 board feet. The retail price on 

February 14, 2007, for rough 4/4 #2 common red oak lumber was $1,430 per thousand board feet. In 2006, wholesale 

price for rough 

4/4 #2 common red oak lumber was $750 per thousand 

board feet on a kiln-dried gross tally (Hardwood Review 

Weekly: August 11, 2006). Therefore, buying only a small 

quantity increases the price to $2.00 per board feet for 

planed, dried #2 common red oak lumber (personal communication on May 15, 2007, with Terry Mace, Forest 

Products Utilization and Management Specialist, Wisconsin 

Table 1—Estimated electrical consumption and cost for the small dry kiln 

Run

No. 

Run time 

(days) 

Electrical use 

(kW-h)

Electrical costa

($)

Charge

(actual bf) 

Cost

($/103 bf) 

Consumption

(kW-h/103 bf) 

2 27 920 46.00 640 72 1,440 

3 44 1,734 86.72 600 145 2,890 

4 29 1,152 57.61 600 96 1,920 a Average electrical power at MATC (2005) is $0.05 per kilowatt-hour, although residential cost is closer to $0.10 per 

 kilowatt-hour. 

Table 2—Cost comparison for the MATC and Post dry kiln 

Cost ($/103

 bf) 

Kiln type Electricity Capital costs Maintenance Labor Transportation Total 

MATC 600 106–159 220 50a

 330 165 871–924 

Post 2500 50 100 50 200 0b

 400 a Maintenance costs for 600-bf kiln assumed to be the same as 2,500-bf kiln. b Lumber was delivered to the facility for drying.
8

Research Note FPL–RN–0310

Department of Natural Resources, Division of Forestry, 

Madison Wisconsin). Based on the initial installed costs of 

$4,800 and operating costs for Run 3 of $740 including lumber, with an expected revenue of $858, the payback period 

would be 4.4 years, assuming 10 runs per year for a total of 

44 runs of 600 board feet of 4/4 #2 common red oak lumber. 

However, using 4/4 #1 common red oak would reduce the 

number of runs to 17 with operating costs of $876 including 

lumber, with revenue of $1,158, for a payback period of 

1.7 years. No equipment failure or other changes are considered during this payback period. Increasing kiln operational 

efficiency was not taken into account for this analysis. Also, 

as noted, using higher valued lumber would give a quicker 

payback.

System Comparison Cost

Values for a 2,500-bf dehumidification kiln were compared 

with the MATC dry kiln (Post 2002). The Post 2500-bf dry 

kiln is over four times larger than the MATC dry kiln and 

uses kiln carts to move lumber in and out of the kiln. Using 

a kiln cart reduces the transient time between the end of one 

cycle and the start of another but increases the amount of 

space required. Transient times are more critical for larger 

operations. Also, track kilns such as the Post 2500 are one of 

the two typical options for larger conventional kilns. For the 

Post 2500, a compressor typical for larger DH kilns is used 

instead of a dehumidifier for the MATC 600. This result 

showed that the larger Post DH dry kiln would cost roughly 

50% less than the MATC dry kiln (Table 2). No forklift is 

included in this comparison, but air-drying the material is 

included in the electrical consumption for the Post 2500. 

Air-drying the material prior to kiln-drying would decrease 

kiln operation time and the amount of electricity used.

Discussion

Several items were noted during the runs: 

•	 A simple timing feature was installed on dehumidifier 

during Day 2 of Run 3 to slow the drying rate to prevent 

drying stresses. Drying stresses had occurred, although 

the highest setting for relative humidity on the dehumidifier was 90%, and this setting was higher than or equal to 

the maximum value any species required for initial drying based on data from AW (2002). After installation, the 

dehumidifier cycled on and off at 6-h increments to prevent exceeding maximum daily moisture loss. However, 

the drying rate was still exceeded for both Runs 3 and the 

northern red oak in Run 4. 

•	 Kiln samples were significantly more accurate in 

calculating moisture loss than measuring volume of 

condensate collected from the dehumidifier. This was 

because the dry kiln was not vapor-tight even though a 

vapor barrier was installed in the walls during construction. We determined this because no condensate was 

collected at later drying stages although the weight of the 

Figure 14—Prong tests for red oak with no conditioning (initial, left; one month later, right).

Table 1—Estimated electrical consumption and cost for the small dry kiln 

Run

No. 

Run time 

(days) 

Electrical use 

(kW-h)

Electrical costa

($)

Charge

(actual bf) 

Cost

($/103 bf) 

Consumption

(kW-h/103 bf) 

2 27 920 46.00 640 72 1,440 

3 44 1,734 86.72 600 145 2,890 

4 29 1,152 57.61 600 96 1,920 a Average electrical power at MATC (2005) is $0.05 per kilowatt-hour, although residential cost is closer to $0.10 per 

 kilowatt-hour. 

Table 2—Cost comparison for the MATC and Post dry kiln 

Cost ($/103

 bf) 

Kiln type Electricity Capital costs Maintenance Labor Transportation Total 

MATC 600 106–159 220 50a 330 165 871–924 

Post 2500 50 100 50 200 0b 400 a Maintenance costs for 600-bf kiln assumed to be the same as 2,500-bf kiln. b Lumber was delivered to the facility for drying.
9

Operation and Cost of a Small Dehumidification Dry Kiln

kiln samples was still decreasing. The main cause was 

that the door seals were not holding; therefore, the seals 

need to be either redesigned or manufactured from a different material.

•	 Calculated electrical consumption on a kW-h per thousand board foot basis was higher than expected because 

of long drying times. Typical commercial dry kilns consumed roughly 500 to 750 kW-h per thousand board foot 

(Denig and others 2000).

o Run 2 (black cherry) was roughly two to three this 

value at 1,440 kW-h

o Run 3 (red oak) was roughly four to six times this 

value at 3,180 kW-h

o Run 4 (mostly red oak) was roughly three to four 

times this value at 2,120 kW-h

•	 Actual run times were very conservative because 

(1) the dehumidifier was assumed to be running full-time, 

although the unit was not usually operating prior to lowering the RH setting; and (2) the dry kiln operated 

5 days longer than required for Run 3. Therefore, the 

lumber was over-dried. Even though the timer cycled the 

dehumidifier on and off, that slowed the drying rate for 

Run 3 (6 h on/6 h off) and the fans ran longer. Run 4 

gave a more accurate value for electrical usage than 

Run 3 because of better control of dehumidifier and 

because the lumber for Run 3 was over-dried. 

•	 The primary drying defect was casehardening. Relieving 

casehardening is vital to producing high-quality lumber 

for wood products. A new method of conditioning for 

Run 4 used a continuous water input into the electric 

steam kettle, which was effective but time consuming.

Recommendations

•	 Original AW (2002) settings for northern red oak were 

too aggressive. Greater control of the dehumidifier 

operation earlier in the kiln schedule would lower the 

amount of casehardening occurring for northern red oak. 

One way to reduce the initial drying rate and resulting 

casehardening for northern red oak is installing additional pins on the timer to shorten the dehumidifier operating 

time for northern red oak to 3 h on and 6 h off. Other 

ways are to install a humidistat to control the 

dehumidifier to allow wider ranges of RH control and decrease the dehumidifier fan speed to low speed for slower 

drying species such as northern red oak. Another option 

is turning off the dehumidifier and fans at night during 

the early stages of drying to slow the drying rate and allow RH to increase, thus conditioning the lumber.

•	 Building and operating small dehumidification dry kilns 

give woodworkers greater control and flexibility of the 

drying process and the entire manufacturing process.

•	 Daily monitoring of the dry kiln is a must, especially in 

the earlier stages of drying.

•	 Increasing the size of the dehumidification dry kiln by 

over four times decreases the overall cost per board foot 

by roughly 50%. Also, custom drying typically cost $300 

per 1,000 board feet (personal communication, E.M. 

Wengert, Professor Emeritus in Wood Processing, Department of Forest Products, Virginia Tech University, 

October 10, 2006). Therefore, preferred uses for this kiln 

are drying small quantities of a select species and working with custom material.

•	 Corroding metal brackets and hinges for the kiln doors 

mostly occurred from kiln-drying northern red oak 

(Fig. 15). Less expensive metal was chosen over stainless steel to determine its effectiveness against corrosion. 

More runs are required to determine the level of corrosion occurring for the current metal. No corrosion was 

found inside the kiln.

References

AW (American Woodworker). 2002. Dry your own wood. 

American Woodworker Magazine. 94: 42–55. 

American Society for Testing and Materials (ASTM). 2002. 

Standard D 2395-02 - Standard test methods for specific 

gravity of wood and wood-based materials. ASTM International, West Conshohocken, PA. http://www.astm.org.

Bond, B. 2006. Design and operation of a solar-heated dry 

kiln. Publication Number 420-030. Blacksburg, VA: Department of Wood Science and Forest Products, Virginia Tech, 

Virginia Cooperative Extension.

Figure 15—Corrosion effect of kiln-drying northern red oak on metal fasteners.
10

Research Note FPL–RN–0310

Bowe, Scott; Molzahn, Patrick; Bond, Brian; Bergman, 

Richard; Mace, Terry; Hubbard, Steve. 2007. Dehumidification drying for small woodworking firms and hobbyists; 

building your own lumber dry kiln with local building materials. PUB-FR-396 2007. Madison, WI: UW Extension–

Wisconsin Department of Natural Resources. 14 p. 

Chen, Peter Y.S.; Helmer, Wayne A. 1987. Designs and tests 

of a solar-dehumidifier kiln with heat storage and heat recovery systems. Forest Products Journal. 37(5):26–30.

Comstock, G.L. 1975. Energy requirements or drying of 

wood products. In: Wood residue as an energy source. 

Proceedings No. P-75-13. Madison, WI: Forest Products 

Research Society: 8–12.

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

hardwood lumber. Gen. Tech. Rep. FPL–GTR–118. Madison, WI: U.S. Department of Agriculture, Forest Service, 

Forest Products Laboratory. 138 p. http://www.fpl.fs.fed.us/

documnts/fplgtr/fplgtr118.pdf.

FPL. 1995. Hardwoods of North America. General Technical Report FPL–GTR–83. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

136 p. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr83.pdf.

FPL. 1999. Wood handbook—wood as an engineering material. General Technical Report FPL–GTR–113. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 463 p. http://www.fpl.fs.fed.us/

documnts/fplgtr/fplgtr113/fplgtr113.pdf.

Fuller, James; Hart, C.A. 1994. In: Proceedings, 4th IUFRO International Wood Drying Conference, Rotorua, New 

Zealand. Factors that influence the prong test. p. 313–320. 

www.fpl.fs.fed.us/documnts/pdf1994/fulle94b.pdf.

Hardwood Review Weekly. 2006. Hardwood Review 

Weekly 22(49):6. Charlotte, North Carolina: Hardwood 

Publishing. 

Peck, Edward C. 1961. Drying 4/4 red oak by solar heat. 

Forest Products Journal. 12(2):103–107.

Post, Irwin. 2002. Drying: how to improve the quality of 

your lumber while reducing your workload. Independent 

Sawmill & Woodlot Management. June/July 2002. 8 p. 

Simpson, W.T. 1991. Dry kiln operator’s manual. Agriculture Handbook AH–188. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

274 p. http://www.fpl.fs.fed.us/documnts/usda/ah188/ah188.

htm.

Simpson, W.T.; Tschernitz, John L. 1984. Solar dry kiln for 

tropical latitudes. Forest Products Journal. 34(5):25–34.

Simpson, W.T.; Tschernitz, John L. 1988. Performance of 

solar/wood energy kiln in tropical latitudes. Forest Products 

Journal. 39(1):23–30.

Tschernitz, John L.; Simpson, William T. 1985. FPL design 

for lumber dry kiln using solar/wood energy in tropical latitudes. General Technical Report FPL–GTR–44. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 17 p.

Wengert, E.M.; Grimm, P.; Lamb, F.; Muench, J. 1988. Opportunities for dehumidification drying of hardwood lumber 

in Virginia. Sandston, VA: Department of Forest Products, 

Virginia Tech University. 34 p.
11

Operation and Cost of a Small Dehumidification Dry Kiln

Appendix A—Bill of Materials

Item Material Quantity Cost/unit ($) Total cost ($) 

Deck 

Runners 4-in. by 4-in. by12-ft TTD 2 11.16 22.32 

Floor 1⁄2-in. by 4-in. by 8-ft. TTD plywood 3 32.84 98.52 

Floor 3⁄4-in by 4-ft by 8-ft CDX 3 28.68 86.04 

Rim joists 2-in. by 8-in. by 12-ft 2 11.77 23.54 

Center blocking 2-in. by 8-in. by 8-ft 1 7.96 7.96 

Rim joists 2-in. by 8-in. by 8-ft 2 7.96 15.92 

Joists 2-in. by 8-in. by 8-ft 7 7.96 55.72 

Insulation 2-in. by 4-in. by 8-ft rigid foam 8 19.89 159.12 

Insulation 1-in. by 4-in. by 8-ft rigid foam 3 9.45 28.35 

Walls 

Studs 2- by 6- by 92-5/8-in. 30 5.92 177.6 

Plates 2- by 6- by 92-5/8-in. 6 5.92 35.52 

Plates 2- by 6- by 12-in. 5 8.81 44.05 

Header 9-1/2-in. LVL (LF) 20 3.09 61.8 

Insulation R-19 Fiberglass Batt (150 SF) 3 14.99 44.97 

Interior sheathing 1⁄2-in. by 4-in. by 8-ft CDX 8 21.01 168.08 

Siding 1⁄2-in. by 4-in. by 8-ft T-111 10 37.53 375.3 

Sill sealer 50-ft roll 1 3.6 3.6 

Corners 1-in. by 4-in. by 8-ft SPF 8 3.36 26.88 

"Z" flashing 1-1/4-in. by 10 ft 5 2.26 11.3 

Water table 2-in. by 4-in. by 10-ft 4 3.73 14.92 

Vapor barrier Roll 1 12.99 12.99 

Doors 

Frames 2-in. by 4-in. by 8-ft SPF 9 2.98 26.82 

Face molding 1-in. by 4-in. by 8-ft SPF 10 3.36 33.6 

Insulation Rigid foam 4 14.65 58.6 

Casing 1-in. by 4-in. by 8-ft SPF 8 3.36 26.88 

Roof 

Rafters 2-in. by 6-in. by 10-ft 7 7.93 55.51 

Sub-fascia 2-in. by 6-in. by 12-ft 2 8.81 17.62 

Fascia 1-in. by 8-in. by 10-ft SPF 2 6.65 13.3 

Fascia 1-in. by 8-in. by 12-ft SPF 2 7.98 15.96 

Soffit 1⁄4-in. by 4- by 8-in. 1 14.5 14.5 

Interior sheathing 1⁄2- by 4-in. by 8-in. CDX 4 21.01 84.04 

Exterior sheathing 1⁄2- by 4- by 8-ft CDX 2 21.01 42.02 

Insulation R-19 fiberglass Batt (100SF) 2 14.99 29.98 

Felt 15# asphalt felt 1 13.94 13.94 

Shingles Fiberglass 4 11.99 47.96 

Drip edge "D" style 10-ft lengths 5 2.78 13.9 

Hardware 

Slide bolts for doors 12 5.47 65.64 

Handles for doors 8 6.24 49.92 

Weather-stripping 70 lF (10-ft/Package) 7 2.56 17.92 

Whole house fans 4 37.99 151.96 

Dehumidifier 30-pint residential model 1 229.00 229.00 

Drain hose 1 5.74 5.74 

Electric baseboard 1 49.98 49.98 

Remote hygrometer/thermometer Radio Shack (Corporation, Fort 

Worth, Texas) Model 63-1030 

1 54.68 54.68 

Miscellaneous 

Exterior stain Gallons 2 20.96 41.92 

Paint for interior Gallons 2 15.98 31.96 

Anchor seal end coating Quarts 2 18.00 36.00 

Total cost of building materials $2,703.85 
12

Research Note FPL–RN–0310

1. Select a few boards from the pack of lumber that represent the slowest drying material. This 

would be the widest, thickest, and highest moisture content boards. Also choose those boards 

that contain the most heartwood or are quartersawn. 

2. Cut a 24–30-in. sample that is free of knots and at least 12 in. from the end of the board. Then 

cut two 1-in. sections from the sample board as shown in (Figure 8). Make sure to number the 

sections and sample board. 

3. Immediately weigh the 1-in. sections (accuracy of about 0.1 g required) and record the weight. 

Measure rapidly after cutting because it is important that the sections do not lose weight 

before weighing. Place in air-tight bag if not able to weigh within a minute or two. 

4. End coat the sample board with either a wax emulsion, rubber-based sealing compound, or 

two coats of aluminum paint. Now, weigh the sample board and record weight on sample 

(accuracy of 0.1 g). 

5. Place 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. 

6. Place the 1-inch sections in an oven 215–218°F (102–103°C) and dry—usually 48 h in an 

oven with good circulation. Reweigh and obtain the oven-dry weight. 

7. Calculate the moisture content (MC) of each section and average the MC of two sections to 

obtain the MC for the sample board. 

1 100

oven dry weight

wet weight %MC u ̧

 ̧

1

·

 ̈

 ̈

©

§ 

8. Estimate ovendry weight of sample board using average MC above and weight from step 4. 

and record so these data can be used for future moisture content calculations to monitor the 

drying rate. 

100

(100 %MC)

wet weight,step 4 Estimated OD weight u

 

9. To determine the moisture content at any time, reweigh the sample board and calculate. 

1 100

Estimated OD weight

current weight Current %MC u  ̧

 ̧

1

·

 ̈

 ̈

©

§ 

Appendix B—Procedure for Cutting and Using Kiln Samples
13

Operation and Cost of a Small Dehumidification Dry Kiln

Appendix C—Drying Schedules

Table 1—Experimental drying schedule for the mixed air-dried wood species (Run #1) 

Date Days 

Average

MCDB (%)

Kiln temperature 

(°F)

Relative humidity 

(%)

Equilibrium moisture 

content (%) 

Dehumidifier 

setting

3/21/2005 0 18.4 — — — 90% 

3/22/2005 1 a 73.9 74 14.0 70% 

3/24/2005 3 16.5 81.6 64 11.5 60% 

3/28/2005 7 13.1 86.0 44 8.1 40% 

3/29/2005 8 a 93.0 38 7.1 35% 

3/30/2005 9 a 95.0 35 6.6 No change 

3/31/2005 10 10.7 93.4 33 6.3 Heater 1200W 

4/1/2005 11 a

 128 23 4.2 Heater off 

4/4/2005 14 7.7 96.1 20 4.2 b

4/5/2005 15 7.3 93.5 18 3.9 End of run 

 a Kiln samples were not weighed on these particular days. b Dehumidifier not running (relative humidity less than 35%). 
14

Research Note FPL–RN–0310

Table 2—Experimental kiln sample record for the mixed air-dried wood species (Run #1)
15

Operation and Cost of a Small Dehumidification Dry Kiln

Table 3—Experimental drying schedule for the green 5/4 black cherry (Run #2) 

Date Days 

Average

MCDB (%)

Kiln temperature 

(°F)

Relative humidity 

(%)

Equilibrium moisture 

content (%) 

Dehumidifier 

setting

9/8/2005 0 47.5 — — — Off 

9/9/2005 1 45.5 75.9 92 21.6% 85% 

9/12/2005 4 a 84.4 93 22.0% 85% 

9/13/2005 5 37.9 97.5 93 21.5% 85% 

9/14/2005 6 a 100 90 19.5% 80% 

9/15/2005 7 a 98.4 87 18.0% 80% 

9/16/2005 8 31.0 90.3 86 17.8% 80% 

9/19/2005 11 23.3 101.7 72 12.7% 70%/65% 

9/20/2005 12 a 103.1 66 11.4% 50% 

9/22/2005 14 a

 105.6 56 9.5% 40% 

9/23/2005 15 14.8 106.2 49 8.4% 35% 

9/27/2005 19 10.4 95.2 35 6.6% b

9/29/2005 21 a 92.5 32 6.2% b

9/30/2005 22 9.1 91 29 5.8% b

10/3/2005 25 8.3 96.8 31 6.0% Heater 1200W 

10/4/2005 26 a

 131.7 20 3.7% Heater 900W 

10/5/2005 27 6.9 123.1 20 3.9% End of run 

 a Kiln samples were not weighed on this particular day. b Dehumidifier not running (relative humidity less than 35%). 
16

Research Note FPL–RN–0310

Table 4—Experimental kiln sample record for the green 4/4 and 5/4 black cherry (Run #2)
17

Operation and Cost of a Small Dehumidification Dry Kiln

Table 5—Experimental drying schedule for the green 4/4 northern red oak (Run #3) 

Date Days 

Average

MCDB (%)

Kiln temperature 

(°F)

Relative humidity 

(%)

Equilibrium moisture 

content (%) 

Dehumidifier 

setting

10/25/2005 0 82.9 60.0 50 9.4 90% 

10/31/2005 6 a 62.6 96 24.9 85% 

11/1/2005 7 a 79.3 97 25.4 85% 

11/1/2005 7 a

 89.4 93 21.8 85% 

11/2/2005 8 a

 86.5 96 24.2 85% 

11/3/2005 9 a

 93.2 93 21.7 85% 

11/4/2005 10 64.5 94.8 90 19.7 80% 

11/7/2005 13 a

 91.0 89 19.3 75% 

11/8/2005 14 a

 95.2 85 17.2 70% 

11/9/2005 15 47.2 97.5 83 16.3 65% 

11/10/2005 16 a

 103 73 13.0 60% 

11/11/2005 17 a

 104 68 11.8 45% 

11/14/2005 20 29.5 99.3 55 10.0 35% 

11/15/2005 21 a

 110 48 8.2 35% 

11/16/2005 22 23.7 111 39 6.9 35% 

11/17/2005 23 a

 109 35 6.4 35% 

11/18/2005 24 a 111 31 5.8 35% 

11/21/2005 27 a 102 26 5.1 35% 

11/22/2005 28 14.7 102 24 4.8 35% 

11/28/2005 34 9.8 106 19 3.9 35% 

11/29/2005 35 a 108 17 3.6 35% 

11/30/2005 36 8.8 106 16 3.4 35% 

12/1/2005 37 a 106 16 3.4 35% 

12/2/2005 38 a

 105 16 3.4 35% 

12/5/2005 41 7.1 106 15 3.2 b

12/6/2005 42 a 104 15 3.2 b

12/7/2005 43 a 104 15 3.2 b

12/8/2005 44 a 104 15 3.2 b

12/9/2005 45 6.1 104 15 3.2 b

12/13/2005 49 a

 107 14 3.0 b

12/14/2005 50 5.2 107 14 3.0 End of run 

 a Kiln samples not weighed on these days. b Dehumidifier not running (relative humidity less than 35%). 
18

Research Note FPL–RN–0310

Table 6—Experimental kiln sample record for the green 4/4 northern red oak (Run #3)
19

Operation and Cost of a Small Dehumidification Dry Kiln

Table 7—Experimental drying schedule for the green 4/4 mixed hardwoods (Run #4) 

Date Days 

Average

MCDB (%)

Kiln temperature 

(°F)

Relative humidity 

(%)

Equilibrium moisture 

content (%) 

Dehumidifier 

setting

8/3/2006 0 69.7 81.1 89 19.6 90% 

8/4/2006 1 a 92.3 94 22.4 85% 

8/7/2006 4 50.8 96.1 88 18.6 85% 

8/9/2006 6 43.1 96.8 81 15.5 85% 

8/14/2006 11 29.7 97.9 64 11.1 60% 

8/15/2006 12 a 103.1 56 9.5 55% 

8/16/2006 13 24.7 104.4 49 8.4 50% 

8/18/2006 15 20.4 105.8 37 6.7 35% 

8/21/2006 18 a 108.3 27 5.2 b

8/22/2006 19 a 110 26 5.0 b

8/23/2006 20 a 113.2 24 4.7 b

8/28/2006 25 a 115 18 3.6 b

8/29/2006 26 a 104 23 4.6 b

8/30/2006 27 a 96.4 26 5.2 b

9/1/2006 29 9.1 80.4 38 7.3 End of run 

 a Kiln samples not weighed. b Dehumidifier not running (relative humidity less than 35%). 
20

Research Note FPL–RN–0310

Table 8—Experimental kiln sample record for the green mixed hardwoods (Run #4)