Heat-Treatment Options 

and Heating Times for 

Ash Firewood 

Xiping Wang

Richard Bergman

William T. Simpson

Steve Verrill

Terry Mace

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

General

Technical

Report

FPL–GTR–187
November 2009

Wang, Xiping; Bergman, Richard; Simpson, William T.; Verrill, Steve; 

Mace, Terry. 2009. Heat-treatment options and heating times for ash 

firewood. General Technical Report FPL-GTR-187. Madison, WI: U.S. 

Department of Agriculture, Forest Service, Forest Products Laboratory. 

29 p.

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Abstract

Because of the potential risk associated with moving 

firewood infested with emerald ash borer, the interstate 

movement of all hardwood firewood is currently restricted 

under Federal quarantine. Communities and firewood 

producers are now faced with decisions on how to treat 

firewood for interstate commerce. New regulations for 

heat sterilization of ash firewood require holding a core 

temperature of 160 °F for 75 min, much higher than the 

current international heating standard for treating solid 

wood packaging. The present study evaluated different 

heat-treatment options for various firewood operations and 

developed heat-treating schedules and heating time tables. 

We first conducted laboratory heating experiments using 

green and air-dried ash firewood and obtained heating time 

data for different heating schemes. Mathematical models 

were developed to estimate heating times for heating 

conditions not tested in the experiment. Heating time tables 

were developed for a series of heating temperatures and 

initial wood temperatures. Our field heat-treatment trial 

in a commercial dry-kiln facility indicated a significant 

difference in heating times between the laboratory kiln runs 

and the field kiln run. Although the size of kiln could have 

contributed to the increase of heating times in the field trial, 

the type of kiln and heat sources are the main factors that 

control the heating rate and result in differences in heating 

times. More field heat-treatment trials at different types of 

kiln facilities (steam, hot water, and direct fire) should be 

conducted in the future to calibrate the heating time tables 

developed through the laboratory experiments.

Keywords: ash firewood, emerald ash borer (EAB), heat 

treatment, dry heat, wet heat

Acknowledgments

This project was funded in part through a grant awarded 

by the Wood Education and Resource Center, Northeastern 

Area State and Private Forestry, Forest Service, U.S. Department of Agriculture (07-DG-114). Materials for laboratory 

experiments were provided by Green Thumb Farms, Inc. 

(Prairie du Sac, Wisconsin) and Norske Wood Works II, Inc. 

(Black Earth, Wisconsin). We especially thank Scott Myers 

and JoAnn Cruse of USDA Animal and Plant Health Inspection Service (APHIS), Andrea Diss-Torrance of Wisconsin 

Department of Natural Resources, and Keith Jacobson of 

Minnesota Department of Natural Resources for providing 

guidance and assistance to the project. We also thank Green 

Thumb Farms for participating in the field heat-treatment 

trial of the study (Prairie du Sac, Wisconsin).

Contents

Page

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

Materials and Methods.........................................................1

 Phase 1—Laboratory Experiments..................................2

 Phase II—Production Trial ..............................................3

Results and Discussion ........................................................3

 Heat-Treating Green Firewood with Moisture

 Reduction (Dry-Heat Schedule).......................................3

 Heat-Treating Green Firewood without Moisture 

 Reduction (Wet-Heat Schedules).....................................7

 Heat-Treating Seasoned Firewood (Dry-Heat 

 Schedules)........................................................................8

 Field Heat-Treatment Trial...............................................8

Summary............................................................................ 10

Literature Cited .................................................................. 11

Appendix A—Predicted Heating Times to a Core 

Temperature of 160 °F for Green Ash Firewood ............... 13

Appendix B—Predicted Heating Times to a Core 

Temperature of 150 °F for Green Ash Firewood ............... 20

Appendix C—Equation for Calculating Upper 

Confidence Bound of Heating Time .................................. 27

Appendix D—Temperature Conversion Table (°F to °C).. 29

Conversion Table 

English unit Conversion factor SI unit 

Btu 1.055 056 × 103 joule (J) 

inch (in.) 25.4 millimeter (mm) 

Temperature 

 increment (°F) 

0.556 Temperature 

 increment (°C) 

cubic feet (ft3

) 0.0283 cubic meter (m)3

Pound (lb) 453.6 gram (g) 
Heat-Treatment Options and Heating Times 

for Ash Firewood

Xiping Wang, Research Forest Products Technologista

Richard Bergman, Research Forest Products Technologist

William T. Simpson, Forest Products Technologist (retired)

Steve Verrill, Mathematical Statistician

Forest Products Laboratory, Madison, Wisconsin

Terry Mace, Forest Utilization and Marketing Specialist

Wisconsin Department of Natural Resources, Madison, Wisconsin

Introduction

Emerald ash borer (EAB), Agrilus planipennis, is a nonnative bark- and wood-infesting insect of Asian origin that 

poses an enormous threat to North American urban and rural 

forests. Since its discovery in southeastern Michigan in 

summer 2002 (Haack and others 2002), EAB has killed millions of ash (Fraxinus spp.) trees in Canada and the United 

States. As of September 2009, the infested area includes two 

Canadian provinces (Ontario and Quebec) and 13 states (Illinois, Indiana, Kentucky, Maryland, Minnesota, Michigan, 

Missouri, New York, Ohio, Pennsylvania, Virginia, West 

Virginia, and Wisconsin) in the United States (Michigan 

State University 2009). The U.S. Forest Service estimates 

that if EAB is not contained or eradicated, it has the potential to cost local governments and homeowners approximately $7 billion (present dollars) over the next 25 years to 

remove and replace dead and dying ash trees (USDA 2008). 

This scenario would also result in extensive environmental 

damage and long-term changes in the North American forest structure. To stop further spread of EAB, quarantines are 

currently in place to prevent infested ash firewood, logs, 

or nursery trees from being transported and starting new 

infestations.

Heat sterilization is currently the most practical and environmentally friendly treatment to kill pests in solid wood materials and prevent the transfer of pests between regions and 

states. Current international regulations for heat sterilization 

of solid wood packaging materials require a minimal core 

temperature of 133 °F for 30 min (FAO 2006; CFR 2004). 

To deal with the potential of EAB moving on firewood, the 

U.S. Department of Agriculture (USDA) Animal and Plant 

Health Inspection Service (APHIS) has implemented a new 

heating standard for treating ash firewood. The new regulations require that the core of the firewood be heated to at 

least 160 °F for a minimum of 75 min (APHIS 2009). Consequently, the heating schedules developed for heat-treating 

solid wood packaging materials are not acceptable for treating firewood.

In heat-treating ash firewood, one practical concern is to 

estimate how long it will take to heat firewood of various 

forms and sizes to the lethal temperature of 160 °F. The 

heating time can vary widely depending on a number of 

factors such as size, wood density, initial moisture content, 

initial wood temperature, heating temperature, and heating medium. Without reasonable estimates of heating time, 

sterilization is at best inefficient in terms of time, energy 

consumption, and equipment usage; and at worst, we risk 

failure to kill the pest and prevent the spread of EAB or 

other non-native invasive species.

The goals of our project were to evaluate different heattreatment options that may suit the needs of various firewood operations and develop heat-treating schedules and 

heating time tables that will help firewood producers to plan 

and execute effective heat-treating operations. The specific 

objectives were the following:

1. Examine different heat-treatment options that meet the 

new heating standard for EAB and suit the needs of 

various firewood operations.

2. Quantify the effects of kiln temperature on the time required to heat the center of ash firewood to 160 °F and 

develop experimental heating time data for different 

heating schemes.

3. Build mathematical models to estimate heating times 

for heating conditions that were not tested in the experiment and develop user-friendly heating time tables that 

cover a range of heating conditions.

4. Examine the applicability of the heating schedules and 

heating time tables in production-scale heat-treatment 

operations through a field trial.

Materials and Methods

This project was conducted in two phases. Phase 1 consisted 

of a series of laboratory heating experiments designed to 

evaluate a variety of heat-treatment schedules suitable 

a This project was completed while Dr. Wang was working as a 

Senior Research Associate at the Natural Resources Research 

Institute of the University of Minnesota-Duluth.
General Technical Report FPL–GTR–187

2

for commercial firewood operations. Phase 2 was a field 

heat-treatment trial designed to examine applicability of 

the heating schedules and heating time tables developed in 

Phase 1 in a production-scale operation.

Phase 1—Laboratory Experiments

Laboratory experiments were designed to heat-treat green 

and seasoned ash firewood to meet the heat-treatment standard for EAB (a minimum firewood core temperature of 

160 °F for a minimum of 75 min) set by USDA APHIS 

(2009). The research approach was to obtain experimental 

data that addressed the most important factors that influence 

heat sterilization of firewood. These are heating medium, 

heating temperature, wood density, initial moisture content, 

and initial wood temperature.

Approximately 23 face cords (980 ft3) of split, barked ash 

firewood in 16- to 18-in. lengths were provided by two local 

firewood producers (a full cord was assumed to equal three 

face cords, 128 ft3) (Fig. 1). The laboratory heating experiments were conducted under three heating schemes, two 

heating schemes for treating green ash firewood and one for 

treating seasoned ash firewood as shown.

1. Dry-heat schedules for heat-treating green ash firewood 

with moisture reduction

•	 Dry-bulb temperature: 160, 170, 180, 200, 240, and 

280 °F

•	 Wet-bulb temperature: allow to seek its own level (no 

water or steam spray)

2. Wet-heat schedules for heat-treating green ash firewood 

without moisture reduction

•	 Dry-bulb temperature: 160, 170, and 180 °F

•	 Wet-bulb depression: 0 and 10 °F (with water or steam 

spray)

3. Dry-heat schedule for heat-treating seasoned 

(< 20% MC) ash firewood

•	 Dry-bulb temperature: 160, 170, and 180 °F

•	 Wet-bulb temperature: allow to seek its own level (no 

water or steam spray)

A total of 15 experimental kiln runs were conducted in the 

laboratory to obtain necessary heating data, including six 

runs for scheme 1, six runs for scheme 2, and three runs for 

scheme 3. Each kiln run contained 1.5 face cords of ash firewood, including various forms and sizes that are normally 

produced by a firewood splitting machine. Thirty of the largest firewood pieces were selected to monitor temperature for 

each kiln run (Fig. 2). Prior to conducting the experimental 

runs, these 30 firewood samples were randomly divided 

into three groups of 10 pieces that were conditioned to three 

different initial temperatures: 1) freezer temperature (0 °F 

chamber); 2) cold temperature (34 °F chamber); and 

3) room temperature (70 °F). The firewood pieces of each 

run were randomly placed within a 4- by 4- by 8-ft steel 

basket to simulate common industry practice, with the monitored samples buried within the pile of firewood (Fig. 3).

Figure 1. Green ash firewood provided by local firewood producers.

Figure 2. Largest firewood samples selected for temperature 

monitoring.

Figure 3. Basket filled with 

firewood with temperaturemonitoring samples buried 

within the pile.
Heat-Treatment Options and Heating Times for Ash Firewood

3

The experimental runs were conducted in an 800-boardfoot research dry kiln at the Forest Products Laboratory in 

Madison, Wisconsin. The kiln has the capacity to reach a 

kiln temperature of 300 °F and create various heating conditions that might be in the practical range of field practice. 

The core temperatures of the 30 firewood samples monitored per run were measured with thermocouples inserted 

to the geometric center of each piece of firewood. Figure 4 

shows a thermocouple wire inserted into a hole and the hole 

plugged with sealant and a round toothpick to prevent ambient kiln air from influencing the thermocouple reading at the 

center. The core temperatures of the firewood samples were 

monitored using a Keithley Model 2700 Multimeter/Data 

Acquisition System (Keithley Instruments, Inc., Cleveland, 

Ohio) and written to computer files at 1-min intervals. The 

data logging system was set to start recording temperature 

data once the kiln door was closed and the kiln started running. For test runs under heating scheme 1, moisture content 

(MC) changes were also monitored by periodically weighing four kiln samples.

Phase II—Production Trial

Three heat-treatment trial runs were conducted in a commercial kiln at Green Thumb Farms, Inc., a firewood 

producer in Prairie du Sac, Wisconsin. The kiln facility at 

Green Thumb Farms includes a hot water boiler (fueled with 

the facility’s waste wood) and a dry kiln with a capacity of 

holding approximately 14 cords of firewood (42 face cords, 

1,792 ft3). Because of insufficient heat capacity, poor air 

circulation, and lack of insulation on hot water pipes, the 

kiln temperature at this facility was limited to 160 °F in winter and 170 °F in summer. Before the heat-treatment trial, 

improvements to the kiln and heating system were made to 

meet the basic temperature requirements of low-temperature 

heating schedules.

•	 Added extra fin pipes inside the kiln to increase heating 

area

•	 Added baffles to improve air circulation inside the kiln

•	 Insulated the hot water pipes between the hot water 

boiler and the kiln

Three field heat-treatment trial runs were conducted 

on April 22–27, August 4–8, and August 19–21, 2008. 

Figure 5 shows the layout of the kiln and locations of the 

firewood samples with thermocouples inserted to monitor 

internal wood temperature. In each trial run, a total of 

27 baskets was used. Baskets were arranged in three levels 

(bottom, middle, and upper), with nine baskets on each 

level. We monitored the core temperatures of six to nine 

firewood samples during trial runs by placing one sample 

into one of the baskets in the bottom level where the air 

temperature is usually lower than that of higher levels.

Green Thumb Farms has been kiln-drying firewood for 

interstate commerce for several years. Firewood loads are 

typically kiln-dried weekly throughout the year. A dry-heat 

schedule that heat-treats the firewood loads with moisture 

reduction would best fit the production needs of the facility. Because the heat energy is provided through a hot water 

boiler (fueled with wood waste), the kiln has limited heating capacity in terms of British thermal units (Btu) and kiln 

temperature. After the kiln improvements were made, we 

expected that the kiln would be capable of reaching 

170 °F in winter and 180 °F in summer. The field trial at 

this facility would allow us to test the dry-heat schedules 

in a low temperature range at 170–180 °F and verify the 

heating times developed from the laboratory experiments.

Results and Discussion

Experimental heating times for ash firewood were determined on the basis of recorded core temperature history for 

each kiln run. This heating time included an initial heating 

period in each test run but did not include the 75-min holding period. The heating time analysis in the present study 

is primarily focused on the temperature requirement of 

the current heat-treatment standard for firewood: 160 °F. 

However, considering that future development may identify 

new temperature–time regimes with lower temperatures but 

longer heating periods, we also derived heating times to a 

center temperature of 150 °F from the same temperature 

history data. 

Heat-Treating Green Firewood with Moisture 

Reduction (Dry-Heat Schedule)

This heat-treating strategy integrates the heat-treatment 

procedures with a kiln-drying process and is considered as 

a primary option by many firewood producers who have 

dry-kiln facilities. The heating medium used is typically dry 

heat (no additional moisture added). The firewood pieces 

are first heated to the target core temperature of 160 °F and 

held for at least 75 min (heat-treatment stage). After the 

Figure 4. A thermocouple inserted into the center of a 

piece of firewood at the middle section.
4

heating standard is met, the firewood loads are continuously 

heated and kiln dried until the moisture content of the firewood reaches 20% or below (kiln-drying stage). The heating capacity of dry-kiln facilities for firewood businesses 

varies widely. Maximum kiln temperature can range from 

below 160 °F to over 280 °F, depending on the types of kiln 

and energy sources used. One major objective of our study 

was to quantify the effects of kiln temperature on the time 

required to heat the center of ash firewood to the target temperature and develop heating time tables that cover a range 

of heating conditions that might be used in field operations. 

In our laboratory heating experiments, the kiln runs for heating scheme 1 were set to a series of dry-bulb temperatures 

(nominal 160, 170, 180, 200, 240, and 280 °F). No water or 

steam spray was introduced, and wet-bulb temperature was 

allowed to seek its own value under each heating condition.

Experimental Heating Times

Tables 1 and 2 summarize the kiln conditions and measured 

heating times to the core temperature of 160 and 150 °F, 

respectively. The heating time to a core temperature of 

160 °F (current heating standard) for ash firewood ranged 

from a few hours at kiln temperatures of 240 and 

280 °F to over 10 h at a kiln temperature of 170 °F. We 

found that initial temperature of firewood had a practical 

effect on heating times when kiln temperature was 200 °F 

and below. As expected, the lower the initial wood 

temperature, the longer the heating time. This implies that 

heat-treating operations in winter should take into account 

initial firewood temperature and plan for longer heating 

times than in warmer seasons.

Conversely, our results showed that initial wood temperature had little effect on heating time when kiln temperature 

was 240 °F and above. This result is likely limited to our 

experimental cases where only two groups of firewood 

samples (10 pieces for each group) were conditioned to cold 

34–36 °F and freezing 11–27 °F temperatures. The remaining pieces of firewood in the basket exhibited the same 

temperature as outside environments where firewood was 

stored. Therefore, a longer heat-up time would be expected 

for a kiln load of frozen firewood compared with just a few 

pieces. We recommend that the effect of initial temperature 

should be properly considered in heat-treatment operations, 

even when kiln temperature is 240 °F and above.

The kiln run with 160 °F dry-bulb temperature failed to 

meet the current heat-treatment standard (160 °F core temperature). This was expected, as we learned from a previous 

study (Simpson and others 2005) that wood core temperature is always below the kiln temperature when the heating 

medium is not saturated steam. This experimental run demonstrated that facilities unable to produce a kiln temperature 

higher than 160 °F will not be able to meet the current EAB 

heat-treatment standard.

General Technical Report FPL–GTR–187

Figure 5. Kiln layout and locations of firewood samples and thermocouples 

for temperature monitoring in the field heat-treatment trial.
5

Heat-Treatment Options and Heating Times for Ash Firewood

Table 1—Summary of experimental heating times to a core temperature of 160 °Fa for green ash 

firewood with dry-heat schedules

Kiln temperature 

setting 

(°F)

Actual kiln temperature (°F) Initial 

temperature 

of firewood 

(°F)

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

 170 167 116 13 471 370 672 

36 411 290 635 

69 396 333 484 

180 176 120 27 251 199 325 

43 232 199 271 

69 198 176 257 

 200 195 128 14 198 164 231 

34 161 143 208 

63 144 94 173 

240 234 155 11 133 92 185 

34 126 109 157 

70 118 89 138 

280 272 160 16 142 103 185 

36 139 104 159 

64 129 83 146 

a

Current regulations from APHIS (2009). 

Table 1—Summary of experimental heating times to a core temperature of 160 °Fa for green ash 

firewood with dry-heat schedules

Kiln temperature 

setting 

(°F)

Actual kiln temperature (°F) Initial 

temperature 

of firewood 

(°F)

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

 170 167 116 13 471 370 672 

36 411 290 635 

69 396 333 484 

180 176 120 27 251 199 325 

43 232 199 271 

69 198 176 257 

 200 195 128 14 198 164 231 

34 161 143 208 

63 144 94 173 

240 234 155 11 133 92 185 

34 126 109 157 

70 118 89 138 

280 272 160 16 142 103 185 

36 139 104 159 

64 129 83 146 

a

Current regulations from APHIS (2009). 

Table 1—Summary of experimental heating times to a core temperature of 160 °Fa for green ash 

firewood with dry-heat schedules

Kiln temperature 

setting 

(°F)

Actual kiln temperature (°F) Initial 

temperature 

of firewood 

(°F)

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

 170 167 116 13 471 370 672 

36 411 290 635 

69 396 333 484 

180 176 120 27 251 199 325 

43 232 199 271 

69 198 176 257 

 200 195 128 14 198 164 231 

34 161 143 208 

63 144 94 173 

240 234 155 11 133 92 185 

34 126 109 157 

70 118 89 138 

280 272 160 16 142 103 185 

36 139 104 159 

64 129 83 146 

a

Current regulations from APHIS (2009). 

Table 2—Summary of experimental heating times to a core temperature of 150 °F for green ash 

firewood with dry-heat schedules

Kiln temperature 

setting 

(°F)

Actual kiln temperature (°F) Initial 

temperature 

of firewood 

(°F)

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

170 167 116 13 291 229 375 

36 276 204 352 

69 258 233 291 

180 176 120 27 187 149 251 

43 170 149 199 

69 145 132 186 

200 195 128 14 165 135 198 

34 132 117 172 

63 118 73 144 

240 234 155 11 110 74 156 

34 101 87 122 

70 93 66 93 

280 272 160 16 124 86 169 

36 122 90 144 

64 111 71 130 

Table 2—Summary of experimental heating times to a core temperature of 150 °F for green ash 

firewood with dry-heat schedules

Kiln temperature 

setting 

(°F)

Actual kiln temperature (°F) Initial 

temperature 

of firewood 

(°F)

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

170 167 116 13 291 229 375 

36 276 204 352 

69 258 233 291 

180 176 120 27 187 149 251 

43 170 149 199 

69 145 132 186 

200 195 128 14 165 135 198 

34 132 117 172 

63 118 73 144 

240 234 155 11 110 74 156 

34 101 87 122 

70 93 66 93 

280 272 160 16 124 86 169 

36 122 90 144 

64 111 71 130 

Table 2—Summary of experimental heating times to a core temperature of 150 °F for green ash 

firewood with dry-heat schedules

Kiln temperature 

setting 

(°F)

Actual kiln temperature (°F) Initial 

temperature 

of firewood 

(°F)

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

170 167 116 13 291 229 375 

36 276 204 352 

69 258 233 291 

180 176 120 27 187 149 251 

43 170 149 199 

69 145 132 186 

200 195 128 14 165 135 198 

34 132 117 172 

63 118 73 144 

240 234 155 11 110 74 156 

34 101 87 122 

70 93 66 93 

280 272 160 16 124 86 169 

36 122 90 144 

64 111 71 130 
6

The results of our laboratory experiments also indicated 

that under the same heating conditions, the heating time to a 

core temperature of 160 °F was substantially longer than the 

time to heat to a core temperature of 150 °F. As an example, 

Figure 6 shows the percentage increase in heating time at 

various heating conditions as the target core temperature 

increases from 150 °F to 160 °F. Note that heating time increase was more prominent when the kiln temperature was 

below 200 °F. This finding supports the incentive of developing a more efficient time–temperature heating regime that 

has a lower core temperature and a longer holding period.

Mathematical Model for Estimating Heating Times

Heating time is affected by both heating conditions and 

physical properties of firewood. No single experiment of 

practical scope would cover them all. Therefore, we developed mathematical models to predict heating times for the 

heating conditions that were not tested in the laboratory 

experiments. Several empirical models were tested, and the 

following four-parameter regression model provided the 

best fit to the experimental data:

where

t is heating time,

T kiln temperature (dry-bulb) (°F), 

T0 initial wood temperature (°F),

W weight of firewood (g), and

l length of firewood (in.).

The geometrical form and size of typical firewood is not 

uniform. We eliminated the size factor in the experiments by 

only selecting the largest pieces of firewood in each experimental run. The weight per unit length (W/l) of the firewood 

samples was included in the model and considered as a 

parameter that accounts for tree species, density, and initial 

moisture content differences.

Heating data from the 160 °F kiln run was excluded from 

regression analysis because the firewood failed to reach the 

target core temperature of 160 °F. In addition, four extreme 

outliers, including one low outlier and three high outliers, 

were removed to ensure that the model would be fit to the 

main body of the data. The low outlier was the result of a 

thermocouple being pulled out of a firewood sample during 

kiln loading, causing an extremely short heating time. The 

three high outliers were from the kiln run with an actual 

average kiln temperature of 167 °F where the three samples 

were likely located in the cold side of the kiln with an air 

temperature of 163 °F. This low temperature was not a representative heating condition for this particular run; therefore, we removed these three high outliers from the main 

body of the experimental data.

Separate regressions were developed for two different target 

core temperatures: 160 and 150 °F. The parameter estimates 

and the associated p-values are provided in Table 3. The 

regression model yielded a reasonably good correlation between predicted heating time and experimental heating data. 

For the multiple regression model of the time to a 

160 °F core temperature, the root mean squared error (after 

predictions have been transformed back into the original 

General Technical Report FPL–GTR–187

0

10

20

30

40

50

60

70

80

90

100

160 180 200 220 240 260 280

Increase of heating times (%)

Initial temp: 63–70 °F

Initial temp: 34–43 °F

Initial temp: 11–27 °F

Kiln temperature (°F)

Figure 6. Percentage increase of heating times as the 

core temperature changes from 150 to 160 °F.

Table 3—Parameter estimates and p-values for the multiple regression 

model 

Coefficient

Model for 71 °C (160 °F) 

core temperature 

Model for 65 °C (150 °F) 

core temperature 

Estimate p-value Estimate p-value

a0 0.534 0.4790 0.703 0.2837 

a1 441.7 0.0001 339.6 0.0001 

a2 –0.108 0.0001 –0.110 0.0001 

a3 0.555 0.0001 0.571 0.0001 

ln(t) = a0 + a1(1/T ) + a2 ln(T0) + a3 ln(W/l)
7

Heat-Treatment Options and Heating Times for Ash Firewood

non-log space) is 69.4 min. The adjusted R2 in the log 

space is 0.694. The correlation between the predicted and 

observed values in the original space is 0.835. Two observations out of the 146 exceeded the corresponding 99% confidence bound on a new observation. For the model 150 °F 

core temperature, the root mean squared error (after predictions have been transformed back into the original non-log 

space) is 36.6 min. The adjusted R2 in the log space is 0.652. 

The correlation between the predicted and observed values 

in the original space is 0.840. No observations out of the 

146 exceeded the corresponding 99% confidence bound on a 

new observation.

Heating Time Tables

Multiple regression models were used to predict heating 

times to core temperatures of both 160 and 150 °F for a 

series of kiln temperatures, initial wood temperatures, and 

weight per unit length. The heating time tables developed 

are shown in Appendices A and B. The tables cover initial 

wood temperature from 10 to 80 °F, representing ambient 

temperatures for different times of the year.

The heating times calculated based on the multiple regression models are average times and provide a general estimate of the time required to heat the center of firewood to 

the target temperature. In any loads of firewood, the average 

time does not ensure that all pieces will achieve the target 

temperature, as we observed considerable variation in 

heating times in these experiments. Therefore, to ensure that 

the heat-treatment target temperature will be attained during the kiln run, the upper 99% statistical confidence bound 

for the heating times was calculated based on the equations 

provided in Appendix C, and the values are provided in Appendices A and B along with the estimated average heating 

times. Appendix D provides a temperature conversion table.

Heat-Treating Green Firewood without 

Moisture Reduction (Wet-Heat Schedules)

This heating strategy applies to situations where firewood 

only needs to be heat-treated to meet the Federal regulations 

and no drying is required. Heating with wet heat (no or low 

wet-bulb depression) is the most efficient way to accomplish 

the heat-treatment goal in this scenario, and it yields much 

shorter heating times than heating with dry heat. 

Tables 4 and 5 show experimental heating times for green 

ash firewood under several different wet-heat conditions, 

which were a combination of three kiln temperatures at 

160, 170, and 180 °F and two wet-bulb depressions at 0 and 

10 °F. The heating times to a core temperature of 160 °F 

were generally in the range of 2 to 4 h in a fully saturated 

heating medium with a kiln temperature of 160 to 180 °F. 

Heating time increased significantly as wet-bulb depression increased from 0 to 10 °F (p ≤ 0.012). As an example, 

Figure 7 shows the effect of heating medium on average 

heating times to core temperatures of 160 and 150 °F for 

Table 4—Summary of experimental heating times to a core temperature of 

160 °Fa

 for green ash firewood with wet-heat schedules

Nominal kiln temperature (°F) Initial wood 

temperature 

(°F)

Heating time (min) 

Dry bulb Wet-bulb depression Average Minimum Maximum 

160 0 76 200 149 239 

160 10 74 229 165 273 

170 0 64 152 114 196 

170 10 53 205 160 241 

180 0 56 151 119 189 

180 10 60 159 124 197 

a

Current regulations from APHIS (2009).

Table 5—Summary of experimental heating times to a core temperature of 

150 °F for green ash firewood with wet-heat schedules

Nominal kiln temperature (°F) Initial wood 

temperature 

(°F)

Heating time (min) 

Dry bulb Wet-bulb depression Average Minimum Maximum 

160 0 76 133 96 173 

160 10 74 162 121 194 

170 0 64 119 91 158 

170 10 53 157 122 194 

180 0 56 124 97 158 

180 10 60 128 100 163 
8

General Technical Report FPL–GTR–187

green ash firewood in a 170 °F kiln temperature. Note that 

under similar initial wood temperature conditions, the heating times for wet-heat schedules at 0 and 10 °F wet-bulb 

depression were significantly lower than the heating times 

for a dry-heat schedule (p < 0.001), and the heating medium 

with 0 °F wet-bulb depression resulted in the shortest heating time.

Heat-Treating Seasoned Firewood (Dry-Heat 

Schedules)

Another scenario for commercial firewood producers is 

heat-treatment of firewood after it has been air-dried. This 

procedure would only be used to meet the Federal regulations in order to freely move firewood from EAB quarantine 

areas.

Although both dry-heat and wet-heat schedules can be used 

to heat-treat seasoned firewood, dry-heat schedules are more 

likely to be used, as firewood producers who air-dry firewood typically do not have a traditional steam kiln.

The experimental heating times for seasoned firewood with 

dry-heat schedules are shown in Tables 6 and 7. The comparison of heating times between green and seasoned firewood is illustrated in Figure 8. The results indicated that 

the heating time for seasoned firewood is significantly less 

than that for green firewood (p ≤ 0.009). In the case of 

170 °F kiln runs, it took about 2 to 4.8 h to heat the seasoned ash firewood to a core temperature of 160 °F, compared with 5.6 to 8 h for green ash firewood.

Field Heat-Treatment Trial

The temperature histories (kiln temperatures and core temperatures of firewood samples) of the three field heat-treatment trial runs are shown in Figures 9 to 11. The first two 

trials failed to meet the current EAB heat-treatment standard 

of 160 °F because of two primary reasons: 1) several water 

0

50

100

150

200

250

300

350

400

450

(10 °F wbd) (0 °F wbd)

A

verage heating time (min)

Heating medium

Dry heat Wet heat Wet heat

Centertemperature 160 °F

Centertemperature 150 °F

Figure 7. Average heating times for green ash firewood 

with dry heat and wet heat schedules (dry-bulb temperature of heating medium: 170 °F. Wbd is wet-bulb 

depression).

Table 6—Summary of experimental heating times to a core temperature of 160 °F a for 

seasoned ash firewood with dry-heat schedulesa

Kiln temperature 

setting (°F) 

Actual kiln 

temperature (°F) Initial temperature

of firewood (°F) 

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum 

22 

160 157 110 42 N/A N/A N/A 

66 

170 167 97 68 223 128 290 

180 176 100 64 169 100 218 

a

Current regulations from APHIS (2009).

Table 7—Summary of experimental heating times to a core temperature of 150 °F for 

seasoned ash firewood with dry-heat schedulesa

Kiln temperature 

setting (°F) 

Actual kiln 

temperature (°F) Initial temperature 

of firewood (°F) 

Measured heating times (min) 

Dry bulb Wet bulb Average Minimum Maximum

 22 269 176 336 

160 157 110 42 237 143 307 

 66 249 189 323 

170 167 97 68 151 89 198 

180 176 100 64 130 78 168 
9

Heat-Treatment Options and Heating Times for Ash Firewood

0

50

100

150

200

250

300

350

400

450

Green

A

verage heating time (min)

Kiln tempearture 170 °F

Kiln temperature 180 °F

Seasoned

Ash firewood

Figure 8. Average heating times to a core temperature of 

160 °F for green and seasoned ash firewood.

0

20

40

60

80

100

120

140

160

180

200

0 8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144

Temperature (°F)

Time (h)

Day 1 Day 2 Day 3 Day 4 Day 5 Day 6

Emerald ash borer standard

Kiln temp 1

(front)

Kiln temp 2

(back)

Firewood 1

Firewood 2

Firewood 3

Firewood 4

Firewood 5

Firewood 6

Figure 9. Temperature record of field heat-treatment trial run #1 conducted on April 

22–27, 2008.
10

General Technical Report FPL–GTR–187

pumps failed during the heating process; 2) the vents were 

not closed in the initial heating stage, causing the kiln to 

lose heat. We also found through these two trials that the 

flow rate of the original water pumps was too low to bring 

sufficient heat into the kiln. Before starting the third trial 

run, Green Thumb Farms replaced all four original pumps 

with new pumps that have a higher flow rate. The following procedures were also implemented in the third trial to 

help raise the kiln temperature: 1) keep the vents closed to 

maintain a high relative humidity within the kiln in the heattreatment stage; 2) open the vents to release moisture after 

the heat-treatment requirement of 160 °F for at least 75 min 

has been met.

The recorded temperature data showed that the third trial 

run passed heat-treatment requirements. The dry-bulb temperature reached 174 °F in the backside of the kiln (lower 

temperature spot). Heating time to the core temperature 

of 160 and 150 °F for green ash firewood in this field trial 

ranged from 13.2 to 15.3 h and 10.1 to 11.8 h, respectively. 

Average heating time for the field trial increased significantly compared with that observed in laboratory experiment with a 170 °F dry-heat schedule. This indicates that the 

type of kiln and energy source have a major effect on actual 

heating times in field heat-treating operations. Hot water 

systems generally have a lower heating capacity compared 

with a traditional steam kiln, which results in lower heating 

rates and longer heating times. Another contributing factor 

is the scale of the kiln and the kiln-load factor. The dry kiln 

at Green Thumb Farms holds 27 baskets of firewood, and 

the laboratory kiln used in the experimental phase of this 

study holds only one basket of firewood. Effect of kiln size 

on heating time is another important consideration for field 

heat-treatment operations.

Summary

In this project, we examined three different heat-treatment 

options that are applicable to a variety of commercial firewood operations. Laboratory heating experiments demonstrated the importance of kiln temperature and kiln humidity 

in meeting the new heat-treatment standard to kill EAB. The 

current primary heat-treatment mode for many firewood 

producers is to use dry-heat schedules to heat-treat and kilndry green firewood in one operation. Based on experimental 

heating data, we developed mathematical models to predict 

average heating times to a core temperature of both 160 and 

150 °F for green ash firewood under various heating conditions. We also developed heating time tables for a series 

of heating temperatures and different initial wood 

0

20

40

60

80

100

120

140

160

180

200

0 8 16 24 32 40 48 56 64 72 80 88 96

Temperature (°F)

Time (h)

Day 1 Day 2 Day 3 Day 4

Emerald ash borer standard

Kiln temp 1

(front)

Kiln temp 2

(back)

Firewood 1

Firewood 2

Firewood 3

Firewood 4

Firewood 5

Firewood 6

Figure 10. Temperature record of field heat-treatment trial run #2 conducted on 

August 4–7, 2008.
11

Heat-Treatment Options and Heating Times for Ash Firewood

temperatures. The tables provide both average heating time 

and the corresponding 99% upper confidence bound. The 

prediction models and heating time tables were developed 

on the basis of laboratory experiments in a small-scale 

dry kiln (approximately 1.5 face cord capacity) with well 

controlled heating conditions and have not been calibrated 

to field operations. Our limited field heat-treatment trials 

indicated a significant difference in heating times between 

laboratory kiln runs and field kiln run. Although the size of 

the kiln could have contributed to increase of heating times 

in field trials, the type of kiln and heat source (hot water 

system) are the main factors that control the heating rate 

and result in differences in heating times. More field heattreatment trials at different types of kiln facilities (steam, 

hot water, and direct fire) should be conducted in the future 

to better calibrate the heating time tables developed in this 

project.

Literature Cited

APHIS. 2009. Treatment schedules T300—Schedules 

for miscellaneous plant products. Washington, DC: U.S. 

Department of Agriculture, Animal and Plant Health Inspection Service. Chapter T314-a Fraxinus (Ash Logs, including 

firewood) and all hardwood firewood from emerald ash borer quarantine areas. http://www.aphis.usda.gov/import_export/plants/manuals/ports/downloads/treatment_pdf/05_04_

t300schedules.pdf

CFR. 2004. Rules and regulations—Importation of wood 

packaging material. U.S. Department of Agriculture, Animal 

and Plant Health Inspection Service 7 Code of Federal Regulations, Part 319. Federal Register 69(179): 55719–55733. 

Washington, DC.

FAO. Food and Agriculture Organization. 2006. International standards for phytosanitary measures: Guidelines for 

regulating wood packaging material in international trade, 

Publication No. 15. (2002, with modifications to Annex 1, 

2006) Rome, Italy: Food and Agriculture Organization of 

the United Nations. 11 pp.

Haack, R.A.; Jendek, E.; Liu, H.; Marchant, K.R.; Petrice, 

T.R.; Poland, T.M.; Ye, H. 2002. The emerald ash borer: 

0

20

40

60

80

100

120

140

160

180

200

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72

Temperature (oF)

Day 1 Day 2 Day 3

Emerald ash 

borer standard

75 min

Kiln temp 1 

(front)

Kiln temp 2 

(back)

Firewood 1

Firewood 2

Firewood 3

Firewood 4

Firewood 5

Firewood 6

Firewood 7

Firewood 8

Firewood 9

Time (h)

Figure 11. Temperature record of field heat-treatment trial run #3 conducted on 

August 19–21, 2008.
12

General Technical Report FPL–GTR–187

a new exotic pest in North America. Newsletter Mich. 

Entomol. Soc. 47 (3&4), 1–5.

Michigan State University. 2009. Emerald ash borer, a multinational effort in Michigan, Illinois, Indiana, Kentucky, 

Maryland, Minnesota, Missouri, New York, Ohio, Pennsylvania, Virginia, West Virginia, Wisconsin, Ontario and Quebec. http://www.emeraldashborer.info/. Accessed September 

9, 2009.

Simpson, W.T.; Wang, X.; Forsman, J.W.; Erickson, J.R. 

2005. Heat sterilization times of five hardwood species. Res. 

Pap. FPL–RP–626. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 10 p. 

USDA. 2008. Emerald ash borer: control may be on the 

horizon. U.S. Department of Agriculture, Forest Service, 

Northern Research Station. Research Review Vol. 2, Winter 

2008. 5 p. 
13

Heat-Treatment Options and Heating Times for Ash Firewood

Appendix A—Predicted Heating Times to a Core Temperature of 160 °F for Green Ash Firewood 

See Appendix D for temperature conversions. Appendix A—Predicted heating times to a core temperature of 160 °F for green ash 

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552
14

Appendix A—Predicted heating times to a core temperature of 160 °F for green ash General Technical Report FPL–GTR–187

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552

180 65 120 179.8 336.2 

180 65 160 210.9 388.9 

180 65 200 238.7 439.6 

180 65 240 264.1 489 

180 65 280 287.7 537.5 

180 80 120 175.8 329

180 80 160 206.3 380.7 

180 80 200 233.4 430.5 

180 80 240 258.3 479

180 80 280 281.3 526.5 

190 10 120 193.5 364.8 

190 10 160 227 420.9 

190 10 200 256.9 474.9 

190 10 240 284.2 527.5 

190 10 280 309.6 578.9 

190 30 120 171.8 320.9 

190 30 160 201.6 370.9 

190 30 200 228.1 418.9 

190 30 240 252.4 465.7 

190 30 280 274.9 511.6 

190 50 120 162.6 303.6 

190 50 160 190.7 351 

190 50 200 215.9 396.7 

190 50 240 238.8 441.2 

190 50 280 260.1 484.8 

190 65 120 158 295.3 

190 65 160 185.4 341.5 

190 65 200 209.8 386.1 

190 65 240 232.1 429.5 

190 65 280 252.9 472.1 

190 80 120 154.5 289 

190 80 160 181.3 334.4 

190 80 200 205.2 378.1 

190 80 240 227 420.7 

190 80 280 247.3 462.4 

200 10 120 172.3 324.6 

200 10 160 202.1 374.5 

200 10 200 228.7 422.6 

200 10 240 253 469.3 

200 10 280 275.6 515.1 

200 30 120 153 285.6 

200 30 160 179.4 330.1 

200 30 200 203.1 372.8 

200 30 240 224.7 414.5 

200 30 280 244.8 455.3 
15

Heat-Treatment Options and Heating Times for Ash Firewood

200 50 120 144.7 270.2 

200 50 160 169.8 312.4 

200 50 200 192.2 353.1 

200 50 240 212.6 392.7 

200 50 280 231.6 431.5 

200 65 120 140.7 262.8 

200 65 160 165 304 

200 65 200 186.8 343.7 

200 65 240 206.7 382.4 

200 65 280 225.1 420.2 

200 80 120 137.6 257.3 

200 80 160 161.4 297.7 

200 80 200 182.6 336.6 

200 80 240 202.1 374.5 

200 80 280 220.1 411.7 

210 10 120 155.1 292.1 

210 10 160 181.9 337.1 

210 10 200 205.9 380.3 

210 10 240 227.8 422.4 

210 10 280 248.1 463.6 

210 30 120 137.7 257.1 

210 30 160 161.5 297.1 

210 30 200 182.8 335.6 

210 30 240 202.3 373.1 

210 30 280 220.3 409.9 

210 50 120 130.3 243.3 

210 50 160 152.8 281.3 

210 50 200 173 317.9 

210 50 240 191.4 353.6 

210 50 280 208.5 388.5 

210 65 120 126.7 236.6 

210 65 160 148.6 273.7 

210 65 200 168.1 309.5 

210 65 240 186 344.3 

210 65 280 202.7 378.4 

210 80 120 123.8 231.6 

210 80 160 145.3 268 

210 80 200 164.4 303.1 

210 80 240 181.9 337.2 

210 80 280 198.2 370.7 

220 10 120 140.9 265.5 

220 10 160 165.3 306.4 

220 10 200 187.1 345.7 

220 10 240 207 384

220 10 280 225.5 421.4 

Appendix A—Predicted heating times to a core temperature of 160 °F for green ash 

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552
16

General Technical Report FPL–GTR–187

220 30 120 125.1 233.8 

220 30 160 146.8 270.1 

220 30 200 166.1 305.1 

220 30 240 183.8 339.2 

220 30 280 200.2 372.6 

220 50 120 118.4 221.2 

220 50 160 138.9 255.7 

220 50 200 157.2 289

220 50 240 173.9 321.5 

220 50 280 189.5 353.3 

220 65 120 115.1 215.2 

220 65 160 135 248.9 

220 65 200 152.8 281.4 

220 65 240 169.1 313 

220 65 280 184.2 344 

220 80 120 112.5 210.6 

220 80 160 132 243.7 

220 80 200 149.4 275.6 

220 80 240 165.3 306.6 

220 80 280 180.1 337

230 10 120 129.1 243.4 

230 10 160 151.5 280.9 

230 10 200 171.5 316.9 

230 10 240 189.7 352 

230 10 280 206.6 386.3 

230 30 120 114.7 214.3 

230 30 160 134.5 247.7 

230 30 200 152.3 279.8 

230 30 240 168.5 311

230 30 280 183.5 341.7 

230 50 120 108.5 202.8 

230 50 160 127.3 234.5 

230 50 200 144.1 265 

230 50 240 159.4 294.8 

230 50 280 173.6 323.9 

230 65 120 105.5 197.3 

230 65 160 123.7 228.2 

230 65 200 140 258

230 65 240 154.9 287

230 65 280 168.8 315.5 

230 80 120 103.1 193.1 

230 80 160 121 223.5 

230 80 200 136.9 252.7 

230 80 240 151.5 281.2 

230 80 280 165 309.1 

Appendix A—Predicted heating times to a core temperature of 160 °F for green ash 

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552
17

Heat-Treatment Options and Heating Times for Ash Firewood

240 10 120 119.2 224.8 

240 10 160 139.8 259.4 

240 10 200 158.3 292.7 

240 10 240 175.1 325.1 

240 10 280 190.8 356.8 

240 30 120 105.9 198 

240 30 160 124.2 228.8 

240 30 200 140.5 258.4 

240 30 240 155.5 287.3 

240 30 280 169.4 315.6 

240 50 120 100.2 187.3 

240 50 160 117.5 216.6 

240 50 200 133 244.8 

240 50 240 147.1 272.3 

240 50 280 160.3 299.2 

240 65 120 97.4 182.3 

240 65 160 114.2 210.9 

240 65 200 129.3 238.4 

240 65 240 143 265.2 

240 65 280 155.8 291.4 

240 80 120 95.2 178.4 

240 80 160 111.7 206.5 

240 80 200 126.4 233.5 

240 80 240 139.9 259.8 

240 80 280 152.3 285.5 

250 10 120 110.8 209 

250 10 160 129.9 241.2 

250 10 200 147 272.1 

250 10 240 162.7 302.2 

250 10 280 177.2 331.7 

250 30 120 98.4 184.1 

250 30 160 115.4 212.7 

250 30 200 130.6 240.3 

250 30 240 144.5 267.1 

250 30 280 157.4 293.4 

250 50 120 93.1 174.2 

250 50 160 109.2 201.4 

250 50 200 123.6 227.7 

250 50 240 136.7 253.2 

250 50 280 148.9 278.2 

250 65 120 90.5 169.5 

250 65 160 106.1 196.1 

250 65 200 120.1 221.7 

250 65 240 132.9 246.6 

250 65 280 144.7 271

Appendix A—Predicted heating times to a core temperature of 160 °F for green ash 

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552
18

General Technical Report FPL–GTR–187 Appendix A—Predicted heating times to a core temperature of 160 °F for green ash 

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552

250 80 120 88.5 165.9 

250 80 160 103.8 192 

250 80 200 117.4 217.1 

250 80 240 129.9 241.6 

250 80 280 141.5 265.5 

260 10 120 103.5 195.4 

260 10 160 121.4 225.5 

260 10 200 137.4 254.4 

260 10 240 152 282.6 

260 10 280 165.6 310.1 

260 30 120 91.9 172.1 

260 30 160 107.8 198.9 

260 30 200 122 224.7 

260 30 240 135 249.8 

260 30 280 147 274.4 

260 50 120 87 162.9 

260 50 160 102 188.4 

260 50 200 115.4 212.9 

260 50 240 127.7 236.8 

260 50 280 139.1 260.2 

260 65 120 84.5 158.5 

260 65 160 99.1 183.4 

260 65 200 112.2 207.3 

260 65 240 124.2 230.6 

260 65 280 135.2 253.4 

260 80 120 82.6 155.2 

260 80 160 96.9 179.6 

260 80 200 109.7 203

260 80 240 121.4 225.9 

260 80 280 132.2 248.3 

270 10 120 97.2 183.6 

270 10 160 114 211.9 

270 10 200 129 239.1 

270 10 240 142.7 265.6 

270 10 280 155.5 291.5 

270 30 120 86.3 161.8 

270 30 160 101.2 187

270 30 200 114.6 211.2 

270 30 240 126.7 234.8 

270 30 280 138.1 257.9 

270 50 120 81.6 153.1 

270 50 160 95.8 177.1 

270 50 200 108.4 200.1 

270 50 240 119.9 222.6 

270 50 280 130.6 244.6 
19

Heat-Treatment Options and Heating Times for Ash Firewood Appendix A—Predicted heating times to a core temperature of 160 °F for green ash 

firewood

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

 (g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 254.4 480.8 

170 10 160 298.4 554.9 

170 10 200 337.7 626.1 

170 10 240 373.6 695.3 

170 10 280 407 763.1 

170 30 120 225.9 422.9 

170 30 160 264.9 488.6 

170 30 200 299.9 551.9 

170 30 240 331.8 613.6 

170 30 280 361.4 674

170 50 120 213.7 399.8 

170 50 160 250.7 462.3 

170 50 200 283.7 522.5 

170 50 240 313.9 581.1 

170 50 280 342 638.6 

170 65 120 207.7 388.9 

170 65 160 243.7 449.8 

170 65 200 275.8 508.5 

170 65 240 305.2 565.7 

170 65 280 332.4 621.7 

170 80 120 203.1 380.6 

170 80 160 238.3 440.4 

170 80 200 269.7 497.9 

170 80 240 298.4 554 

170 80 280 325 608.9 

180 10 120 220.2 415.5 

180 10 160 258.3 479.5 

180 10 200 292.3 541

180 10 240 323.4 600.8 

180 10 280 352.3 659.4 

180 30 120 195.5 365.5 

180 30 160 229.3 422.3 

180 30 200 259.6 477 

180 30 240 287.2 530.3 

180 30 280 312.8 582.5 

180 50 120 185 345.6 

180 50 160 217 399.7 

180 50 200 245.6 451.7 

180 50 240 271.8 502.4 

180 50 280 296 552

270 65 120 79.4 149

270 65 160 93.1 172.4 

270 65 200 105.4 194.9 

270 65 240 116.6 216.8 

270 65 280 127 238.2 

270 80 120 77.6 145.8 

270 80 160 91 168.8 

270 80 200 103 190.9 

270 80 240 114 212.4 

270 80 280 124.2 233.4 
20

General Technical Report FPL–GTR–187

Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 

Appendix B—Predicted Heating Times to a Core 

Temperature of 150 °F for Green Ash Firewood. 

See Appendix D for temperature conversions.
21

Heat-Treatment Options and Heating Times for Ash Firewood

180 65 120 129.5 222.9 

180 65 160 152.6 259.5 

180 65 200 173.3 294.5 

180 65 240 192.3 328.3 

180 65 280 209.9 361.3 

180 80 120 126.5 218.1 

180 80 160 149.1 254

180 80 200 169.4 288.2 

180 80 240 187.9 321.4 

180 80 280 205.2 353.7 

190 10 120 144 249.7 

190 10 160 169.6 290.1 

190 10 200 192.7 328.6 

190 10 240 213.8 365.8 

190 10 280 233.4 402.1 

190 30 120 127.6 219.6 

190 30 160 150.4 255.4 

190 30 200 170.8 289.6 

190 30 240 189.5 322.7 

190 30 280 206.9 354.9 

190 50 120 120.6 207.5 

190 50 160 142.2 241.5 

190 50 200 161.5 274 

190 50 240 179.2 305.4 

190 50 280 195.7 336 

190 65 120 117.2 201.8 

190 65 160 138.1 234.9 

190 65 200 156.9 266.5 

190 65 240 174.1 297.1 

190 65 280 190.1 327

190 80 120 114.6 197.4 

190 80 160 135 229.8 

190 80 200 153.4 260.8 

190 80 240 170.2 290.9 

190 80 280 185.8 320.1 

200 10 120 131.6 228.2 

200 10 160 155.1 265.2 

200 10 200 176.2 300.4 

200 10 240 195.5 334.4 

200 10 280 213.5 367.6 

200 30 120 116.7 200.8 

200 30 160 137.5 233.5 

200 30 200 156.2 264.7 

200 30 240 173.3 295 

200 30 280 189.2 324.5 

Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 
22

General Technical Report FPL–GTR–187

200 50 120 110.3 189.7 

200 50 160 130 220.8 

200 50 200 147.7 250.5 

200 50 240 163.9 279.2 

200 50 280 178.9 307.2 

200 65 120 107.2 184.5 

200 65 160 126.3 214.8 

200 65 200 143.5 243.7 

200 65 240 159.2 271.7 

200 65 280 173.8 299 

200 80 120 104.8 180.5 

200 80 160 123.5 210.2 

200 80 200 140.2 238.5 

200 80 240 155.6 266

200 80 280 169.9 292.7 

210 10 120 121.4 210.5 

210 10 160 143.1 244.5 

210 10 200 162.5 277 

210 10 240 180.3 308.4 

210 10 280 196.9 339 

210 30 120 107.6 185.2 

210 30 160 126.8 215.4 

210 30 200 144.1 244.2 

210 30 240 159.8 272.1 

210 30 280 174.5 299.3 

210 50 120 101.8 175 

210 50 160 119.9 203.7 

210 50 200 136.2 231.1 

210 50 240 151.1 257.6 

210 50 280 165 283.4 

210 65 120 98.9 170.2 

210 65 160 116.5 198.1 

210 65 200 132.3 224.8 

210 65 240 146.8 250.6 

210 65 280 160.3 275.8 

210 80 120 96.6 166.5 

210 80 160 113.9 193.9 

210 80 200 129.4 220 

210 80 240 143.5 245.4 

210 80 280 156.7 270 

220 10 120 112.8 195.6 

220 10 160 132.9 227.2 

220 10 200 151 257.4 

220 10 240 167.5 286.6 

220 10 280 183 315

Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 
23

Heat-Treatment Options and Heating Times for Ash Firewood

220 30 120 100 172.1 

220 30 160 117.8 200.2 

220 30 200 133.8 227 

220 30 240 148.5 252.9 

220 30 280 162.2 278.2 

220 50 120 94.5 162.7 

220 50 160 111.4 189.3 

220 50 200 126.5 214.8 

220 50 240 140.4 239.4 

220 50 280 153.3 263.4 

220 65 120 91.9 158.2 

220 65 160 108.3 184.2 

220 65 200 123 209 

220 65 240 136.4 233 

220 65 280 149 256.4 

220 80 120 89.8 154.8 

220 80 160 105.8 180.2 

220 80 200 120.2 204.5 

220 80 240 133.4 228.1 

220 80 280 145.6 251

230 10 120 105.5 182.9 

230 10 160 124.3 212.5 

230 10 200 141.2 240.8 

230 10 240 156.7 268 

230 10 280 171.1 294.6 

230 30 120 93.5 161

230 30 160 110.2 187.3 

230 30 200 125.2 212.3 

230 30 240 138.9 236.6 

230 30 280 151.6 260.2 

230 50 120 88.4 152.2 

230 50 160 104.2 177.1 

230 50 200 118.3 200.9 

230 50 240 131.3 224 

230 50 280 143.4 246.5 

230 65 120 85.9 148

230 65 160 101.2 172.3 

230 65 200 115 195.5 

230 65 240 127.6 218

230 65 280 139.3 239.9 

230 80 120 84 144.8 

230 80 160 98.9 168.6 

230 80 200 112.4 191.4 

230 80 240 124.7 213.4 

230 80 280 136.2 234.9 

Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 
24

General Technical Report FPL–GTR–187 Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 

240 10 120 99.2 172.1 

240 10 160 116.9 200

240 10 200 132.8 226.5 

240 10 240 147.3 252.2 

240 10 280 160.9 277.2 

240 30 120 87.9 151.5 

240 30 160 103.6 176.2 

240 30 200 117.7 199.8 

240 30 240 130.6 222.6 

240 30 280 142.6 244.9 

240 50 120 83.1 143.2 

240 50 160 98 166.7 

240 50 200 111.3 189.1 

240 50 240 123.5 210.8 

240 50 280 134.8 231.9 

240 65 120 80.8 139.3 

240 65 160 95.2 162.1 

240 65 200 108.1 184 

240 65 240 120 205.1 

240 65 280 131 225.7 

240 80 120 79 136.3 

240 80 160 93 158.7 

240 80 200 105.7 180.1 

240 80 240 117.3 200.8 

240 80 280 128 221

250 10 120 93.7 162.7 

250 10 160 110.5 189.1 

250 10 200 125.5 214.2 

250 10 240 139.2 238.4 

250 10 280 152 262.1 

250 30 120 83.1 143.2 

250 30 160 97.9 166.6 

250 30 200 111.2 188.9 

250 30 240 123.4 210.5 

250 30 280 134.8 231.5 

250 50 120 78.6 135.4 

250 50 160 92.6 157.6 

250 50 200 105.1 178.8 

250 50 240 116.7 199.3 

250 50 280 127.4 219.3 

250 65 120 76.3 131.7 

250 65 160 89.9 153.3 

250 65 200 102.2 174

250 65 240 113.4 194

250 65 280 123.8 213.5 
25

Heat-Treatment Options and Heating Times for Ash Firewood

250 80 120 74.6 128.9 

250 80 160 87.9 150.1 

250 80 200 99.9 170.3 

250 80 240 110.8 189.9 

250 80 280 121 209 

260 10 120 89 154.5 

260 10 160 104.8 179.5 

260 10 200 119.1 203.4 

260 10 240 132.1 226.4 

260 10 280 144.3 248.9 

260 30 120 78.9 136 

260 30 160 92.9 158.2 

260 30 200 105.6 179.4 

260 30 240 117.1 199.9 

260 30 280 127.9 219.9 

260 50 120 74.6 128.6 

260 50 160 87.9 149.7 

260 50 200 99.8 169.8 

260 50 240 110.7 189.3 

260 50 280 120.9 208.3 

260 65 120 72.4 125.1 

260 65 160 85.4 145.6 

260 65 200 97 165.3 

260 65 240 107.6 184.3 

260 65 280 117.5 202.8 

260 80 120 70.8 122.4 

260 80 160 83.4 142.6 

260 80 200 94.8 161.8 

260 80 240 105.2 180.4 

260 80 280 114.8 198.5 

270 10 120 84.8 147.3 

270 10 160 99.9 171.2 

270 10 200 113.5 193.9 

270 10 240 125.9 215.9 

270 10 280 137.5 237.3 

270 30 120 75.1 129.7 

270 30 160 88.5 150.9 

270 30 200 100.6 171.1 

270 30 240 111.6 190.6 

270 30 280 121.9 209.7 

270 50 120 71 122.7 

270 50 160 83.7 142.8 

270 50 200 95.1 162 

270 50 240 105.5 180.5 

270 50 280 115.2 198.6 

Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 
26

General Technical Report FPL–GTR–187 Appendix B—Predicted heating times to a core temperature of 150 °F for green ash 

firewood. See Appendix D for temperature conversions.

Kiln

temperature 

(°F)

Initial wood 

temperature (°F) 

Unit weight 

length 

(g/in.) 

Heating time (min) 

Predicted 

99% upper 

confidence bound

170 10 120 177.6 308.9 

170 10 160 209.3 358.9 

170 10 200 237.8 406.5 

170 10 240 263.8 452.5 

170 10 280 288.1 497.4 

170 30 120 157.5 271.5 

170 30 160 185.6 315.8 

170 30 200 210.8 358.1 

170 30 240 233.9 398.9 

170 30 280 255.4 438.8 

170 50 120 148.9 256.5 

170 50 160 175.4 298.6 

170 50 200 199.3 338.7 

170 50 240 221.1 377.5 

170 50 280 241.4 415.4 

170 65 120 144.7 249.4 

170 65 160 170.5 290.3 

170 65 200 193.6 329.4 

170 65 240 214.8 367.2 

170 65 280 234.6 404.1 

170 80 120 141.4 244 

170 80 160 166.6 284.1 

170 80 200 189.2 322.4 

170 80 240 210 359.5 

170 80 280 229.3 395.6 

180 10 120 159 276

180 10 160 187.3 320.7 

180 10 200 212.8 363.2 

180 10 240 236.1 404.4 

180 10 280 257.8 444.5 

180 30 120 140.9 242.7 

180 30 160 166.1 282.3 

180 30 200 188.6 320 

180 30 240 209.3 356.6 

180 30 280 228.5 392.2 

180 50 120 133.2 229.3 

180 50 160 157 266.9 

180 50 200 178.3 302.8 

180 50 240 197.9 337.5 

180 50 280 216.1 371.3 

270 65 120 69 119.3 

270 65 160 81.3 138.9 

270 65 200 92.4 157.6 

270 65 240 102.5 175.7 

270 65 280 111.9 193.3 

270 80 120 67.5 116.7 

270 80 160 79.5 135.9 

270 80 200 90.3 154.3 

270 80 240 100.2 172 

270 80 280 109.4 189.3 
27

Heat-Treatment Options and Heating Times for Ash Firewood

30

Appendix C—Equation for Calculating Upper Confidence Bound of 

Heating Time 

The general formula for an upper (1 – α) × 100% confidence bound on a new observation (heating time) at predictor 

vector x is 

x   x   x

1

dof 1 1 ˆ   t   s   X X T T T    (A–1) 

where tdof (1 – α) is the appropriate critical value from a Student’s t distribution, s is the root mean residual sum of 

squares from the regression, and X is the design matrix for the regression. 

For the multiple regression model, 

  0 1 1 2 2 3 3 ln t  a  a x  a x  a x (A–2) 

where 































3

2

1

1

x

x

x

x

 

(A–3) 

1 0.00493699 0.00085843 x1  T  (A–4) 

ln 3.50324182 0.66897527 x2  T0  (A–5) 

ln  5.23485105 0.15586916 x3  W l  (A–6) 

The appropriate tdof (1 – α) value for a 99% confidence bound is 2.3529 for heating time prediction to both 160 and 

150 °F center temperature. 

For the heating time prediction to a center temperature of 160 °F, 





























 





























 0.08647

0.07234

 0.37915

 5.23953

3

2

1

0









(A–7) 

s = 0.25714 (A–8) 

For heating time prediction to a center temperature of 150 °F, 





























 





























 0.08894

0.07342

 0.29152

 4.98222

3

2

1

0









(A–9) 
31

s = 0.22339 (A–10) 

For both the 160 and 150 °F predictions, 

 

























     

     

     

     

 

1.342262E 10 3.212628E 05 8.306181E 04 6.994486E 03

3.283614E 09 7.859142E 04 7.082774E 03 8.306181E 04

2.918086E 08 6.984271E 03 7.859142E 04 3.212628E 05

6 849315E 03 2.918086E 08 3.283614E 09 1.342262E 10

1

.

X XT (A–11)

28

General Technical Report FPL–GTR–187
Appendix D—Temperature conversion table (°F–°C)a

°F °C °F °C °F °C °F °C °F °C

31 –1 71 22 111 44 151 66 191 88

32 0 72 22 112 44 152 67 192 89

33 1 73 23 113 45 153 67 193 89

34 1 74 23 114 46 154 68 194 90

35 2 75 24 115 46 155 68 195 91

36 2 76 24 116 47 156 69 196 91

37 3 77 25 117 47 157 69 197 92

38 3 78 26 118 48 158 70 198 92

39 4 79 26 119 48 159 71 199 93

40 4 80 27 120 49 160 71 200 93

41 5 81 27 121 49 161 72 201 94

42 6 82 28 122 50 162 72 202 94

43 6 83 28 123 51 163 73 203 95

44 7 84 29 124 51 164 73 204 96

45 7 85 29 125 52 165 74 205 96

46 8 86 30 126 52 166 74 206 97

47 8 87 31 127 53 167 75 207 97

48 9 88 31 128 53 168 76 208 98

49 9 89 32 129 54 169 76 209 98

50 10 90 32 130 54 170 77 210 99

51 11 91 33 131 55 171 77 211 99

52 11 92 33 132 56 172 78 212 100

53 12 93 34 133 56 173 78 213 101

54 12 94 34 134 57 174 79 214 101

55 13 95 35 135 57 175 79 215 102

56 13 96 36 136 58 176 80 216 102

57 14 97 36 137 58 177 81 217 103

58 14 98 37 138 59 178 81 218 103

59 15 99 37 139 59 179 82 219 104

60 16 100 38 140 60 180 82 220 104

61 16 101 38 141 61 181 83 221 105

62 17 102 39 142 61 182 83 222 106

63 17 103 39 143 62 183 84 223 106

64 18 104 40 144 62 184 84 224 107

65 18 105 41 145 63 185 85 225 107

66 19 106 41 146 63 186 86 226 108

67 19 107 42 147 64 187 86 227 108

68 20 108 42 148 64 188 87 228 109

69 21 109 43 149 65 189 87 229 109

70 21 110 43 150 66 190 88 230 110

a

Conversion formula: T°C = (T°F – 32)/1.8 

Appendix D—Temperature Conversion 

Table (°F to °C)a

29

Heat-Treatment Options and Heating Times for Ash Firewood