Dry kiln production in the northeastern United States

The NE/NC region is a significant contributor to the national hardwood lumber supply, with 53 percent of all hardwood sawlog roundwood received by mills located in this region (USDA Forest Service, Forest Inventory and Analysis, Timber Product Output 2025). Nationally, approximately 5.0 BBF of hardwood lumber was kiln dried annually between 1992 and 1993, compared to 24.0 BBF of softwood (Rice et al. 1994). In the North region of that study (very similar to the NE/NC region for this study), 3.4 BBF of lumber (hardwood and softwood) was kiln dried annually, representing 79.1 percent of total (green) regional lumber production (Rice et al. 1994).

The species composition in the NE/NC region is diverse. Based on average annual harvest removals of sawlog wood volume, the leading harvest species in the NE/NC region currently are red oak (19.1%), hard maple (13.1%), soft maple (13.0%), white oak (10.8%), aspen (9.8%), ash (7.3%), cherry (5.9%), and yellow-poplar (5.8%) (USDA Forest Service, Forest Inventory and Analysis Program 2025). Comparing this data set to a 20-mill study of the region by Bergman and Bowe (2008), red oak and yellow-poplar have lost share while soft maple has gained share. This change highlights in part the influence of market demand on processed species.

Dry kiln characteristics and challenges in the northeastern United States

The North region’s dry kiln infrastructure in 1992 to 1993 included over 2,800 dry kilns with a collective holding capacity of 130.5 million board feet (MMBF). Steam-heated kilns were predominant (2,503 units), followed by dehumidifier (273 units) and direct-fired kilns (49 units). Predryers (129 units, 60.4 MMBF capacity) and fan-shed dryers (21 units, 4.9 MMBF capacity) were also used for initial moisture reduction (Rice et al. 1994).

There is a persistent need for upgrading or overhauling existing old and inefficient dry kiln facilities and a demand for better precision and accuracy in maintaining kiln temperatures and fan speeds (Bergman and Bowe 2008). Other studies also have found that kiln corrosion and structure deterioration were significant problems for kiln operations (Little and Moschler 1993). This suggests that aging equipment potentially results in below-optimal kiln efficiency.

Kiln operations face challenges such as inadequate heating, humidification, and air circulation in older kilns, hindering effective drying of green hardwoods. In addition, insufficient venting can lead to slow drying and stain (Denig et al. 2000). Common operational problems include airflow issues, maintenance needs, and challenges in optimizing schedules (Alexiadis et al. 2007). Even minor deviations can profoundly affect drying quality; a few degrees difference in dry-bulb temperature can significantly change relative humidity and equilibrium moisture content (Denig et al. 2000).

Wood-drying technology has advanced, with modern kilns incorporating computer controls for precise regulation (Denig et al. 2000). Innovations include heat recovery ventilation systems for reduced fuel consumption and new retrofittable control systems with advanced features like mobile phone/Web-based controls (Elustondo et al. 2023). Artificial intelligence is also being explored for timber drying modeling and control to mitigate defects and enhance productivity (Uwizeyimana et al. 2020, Nyle Dry Kilns innovates 2023). Small dehumidification kilns (e.g., around 800 board feet of capacity with cost as low as $3,000) offer economical solutions for portable sawmill owners (Bennett 2013). Despite these advancements, adoption of new technology in the forest products industry can be slow, influenced by economic factors and raw material heterogeneity (Rosenberg et al. 1990). Smaller wood products firms, which comprise a significant portion of the industry, also have been shown to face unique challenges in seeking information and making business investments (Buehlmann et al. 2013).

Stakeholder knowledge and training opportunities

Proper operator training is fundamentally important for achieving high-quality drying and preventing costly defects. A proficient kiln operator must understand basic drying concepts, select and monitor kiln samples, operate and maintain equipment, and adhere to schedules, all of which directly impact product quality and profitability (Denig et al. 2000). Even with automation, modern drying systems rely on human operators for proper setup, calibration, and data interpretation; drying quality ultimately depends on operating procedures, not solely equipment. Automated moisture control systems still require daily visual inspection for defects and malfunctions, especially for high-moisture content (MC) and check-prone species (Denig et al. 2000). Issues from inadequate drying cascade into increased waste and rework in secondary manufacturing, underscoring the need for advanced technology and comprehensive operator training.

The previously mentioned Canadian study, while not a US-focused study, indicated that kiln operators were perceived as the most knowledgeable group regarding kiln drying issues, followed by equipment suppliers, distributors, sales personnel, and customers (Alexiadis et al. 2007). However, those authors also noted that “dried product quality problems were only considered to be moderately serious issues,” (Alexiadis et al. 2007, page 192) possibly due to the Canadian industry’s focus on primary wood products and volume maximization and less concerned about product quality. This suggests a training need to emphasize the business case for quality drying across all stakeholders.

University extension services and continuing education courses offer training programs to impart practical and scientific knowledge about lumber drying (North Carolina [NC] State University 2025). Examples include the aforementioned GLKDA short course and the NC State Dry Kiln Operator’s Short Course. These courses benefit new and experienced operators, as well as supervisors, sales personnel, and marketing personnel, often combining classroom learning with hands-on exercises.

Response rate

In total, 202 usable questionnaires were returned. After accounting for undeliverable mailings (n = 52) and responding firms without kilns (n = 143), the adjusted response rate was 33.6 percent, which was similar to the average response rate reported in other published forest products survey research (Bumgardner et al. 2017). As a check for nonresponse bias (Armstrong and Overton 1977), earlier respondents (wave 1, n = 156) were compared to later respondents (wave 2 responding after the second mailing, n = 43) using 2 by 2 chi-square tests for two variables regarding firm size and type. No differences were found based on whether firms had fewer than 20 employees or 20+ employees (p = 0.49), or whether their drying operations were integrated with other processes (p = 0.65). Therefore, nonresponse bias was not considered to be a significant problem with the study.

Trained data entry operators entered the responses into a CASES software-programmed data entry instrument. The data entry instrument included the questions as they appeared in the survey instrument and automatically checked that numeric codes were valid and implemented any skip patterns in the instrument. Comments that respondents made on the paper instruments were entered and delivered to the researchers.

Characteristics of the NE/NC drying industry

Series of questions were included in the study to determine which lumber species, volume percentage, and thickness percentage were being dried. Respondents were asked to indicate if they dried each species in 2023, along with categories for the percentage that was 4/4 thickness (∼1 inch). Overall, 85.4 percent of respondents dried hardwood lumber and 46.7 percent of respondents dried softwood lumber. As shown in Table 1, red oak was being dried by 89 percent of the respondents that dried hardwoods. Red oak was followed by soft maple, white oak, cherry, and hard maple, respectively, with each representing more than 80.0 percent of respondents. These results are generally consistent with the harvest removal data discussed previously. For softwoods, white pine boards were by far the most common species and product dried.

Table 1.What lumber species and products does your facility dry?

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We were interested in the percentage of 4/4 thickness lumber produced across the study area. Table 2 shows the percentage of responding firms with all their drying volume consisting of 4/4 thickness lumber along with other categories for each species. Overall, these numbers were somewhat lower than expected for the higher percentages and might indicate that dryers are being asked to process more customized orders. Additionally, we expected that small firms would tend to dry more 4/4 lumber as a percentage of their total drying. However, no significant differences were found across firm sizes for any of the major species dried.

Table 2.Percentage of firms drying 100 percent, 75 to 99 percent, 50 to 74 percent, and less than 50 percent 4/4 thickness (1 inch) hardwood lumber, by species.

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Technology and tools used and investments planned

Several drying tools and processes were examined for their frequency of use (Table 3). Smaller facilities were less likely than midsize and large facilities to use kiln samples, apply end coatings, use steam kilns, and purchase green lumber to dry. Less than half of small facilities used any of these tools/processes (Table 3). The gap between smaller and large facilities was especially large for steam kilns, with only 14 percent of smaller firms using them. This is not surprising given the boiler requirement needed to use steam. Overall, 49.2 percent of responding firms were operating steam kilns. Other nonsteam drying systems are available with lower costs to entry; qualitatively, respondents reported dehumidification kilns as a common alternative, and a few were using vacuum and solar kilns. Finally, smaller facilities were more likely to manufacture their own stickers. This data result is useful for our dry kiln operators’ short course. For example, there is a need to stress the use of kiln samples, end coatings, and proper sticker manufacturing to improve quality in the final dried lumber product.

Table 3.Does your facility use the following tools/processes when kiln drying?

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There are a variety of sticker types available in the commercial lumber drying market. Stickers are designed to improve lumber quality by increasing airflow. Advancements in sticker technology include reducing surface area contact with boards and extending sticker life by using high-specific-gravity species. As shown in Table 4, small firms were significantly different from medium and large firms in their use of these “specialty” stickers. This is not surprising, since commercially available specialty stickers are significantly more costly than homemade stickers. Future industry training could seek to help smaller firms improve their sticker use.

Table 4.What types of stickers does your facility use?

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Custom drying for small-scale use has been a key fee for service offered by small firms for many years and is clearly shown in the results (Table 5). Nearly 80 percent of the respondents in the smallest production category custom dry for small-scale use. On the other hand, less than half of respondents in all size classes custom dry for commercial use, suggesting that commercial users are looking for larger production runs. Still, the fact that nearly half of respondents are also custom drying for commercial users also shows the importance of customization in the hardwood industry.

Table 5.Does your facility custom dry lumber for the following markets?

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Future investments

Respondents were asked about their investment plans for new drying equipment over the next 3 years. Significant differences were found among firm sizes for the “no investments planned” option, with more smaller firms in agreement. For those respondents that planned to invest in the next 3 years, 52.0 percent planned to invest $100,000 or less, and 48.0 percent planned to invest more than $100,000 (Table 6).

Table 6.Over the next 3 years, what are your investment plans for new drying equipment?

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Similarly, respondents were asked about investment plans for kiln upgrades or repairs, such as controls, coils, vents, or structural panels. Again, significant differences were found among firm sizes for the “no investments planned” option, with more smaller firms in agreement. For those respondents that planned to invest in upgrades or repairs in the next 3 years, 79.5 percent planned to invest $100,000 or less, and 20.5 percent planned to invest more than $100,000 (Table 7).

Table 7.Over the next 3 years, what are your investment plans for kiln upgrades or repairs, such as controls, coils, vents, or structural panels?

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Integrated processes with drying

We were interested in process integration and asked a series of questions about integrated production in addition to dry kiln facilities. It was expected that drying firms would be providing additional services, given the increased focus on customization in the industry, especially related to sorting lumber products and special grading (Espinoza et al. 2011). Overall, 85.3 percent of respondents indicated they had some form of integrated production at their facility. Differences by firm size are shown in Table 8. Small firms were more likely to have a sawmill, although most respondents in all size categories had a sawmill. Larger facilities provided more sorting and grading services than smaller facilities. For example, over 96 percent of larger facilities provided width sorting, while only 50 percent of smaller firms provided width sorting. Only 27 percent of smaller facilities provided color sorting, while 71 percent of larger firms provided this service. Most facilities across sizes provided width ripping and planing services (especially planing). About half of all facilities also produced dimension components, regardless of size (Table 8).

Table 8.Which of the following integrated processes does your facility have?

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Training needs and priorities

Study questions examined issues related to drying processes, kiln control, and quality control to help identify training needs for the industry. Related to drying processes, there were clear differences by firm size in the importance of several processes (Table 9). In general, small firms were less likely to see the drying process issues as important (respondents were placed into a combined very/extremely important category for analysis), likely as a function of the smaller and less intensive nature of their facilities relative to larger firms. This was especially true for maintenance and repairs and use of optimized schedules. Energy consumption and kiln layout selection were areas where small firms responded similarly to larger firms. For small firms, airflow was rated as the most important drying process issue.

Table 9.How important are the following drying process issues to you?

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A similar pattern was observed with the perceived importance of kiln control issues, with small firms generally rating them as less important than larger firms (Table 10). However, kiln control issues were rated relatively highly by small firms as well (a majority rated each one as very or extremely important), suggesting training on control issues would appeal to all firm size categories.

Table 10.How important are the following kiln control issues to you?

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Lastly, defect issues (i.e., quality control) in lumber drying were examined. Small firms struggled most with MC and warping issues relative to larger firms, with over 40 percent of small firms rating these issues as very or extremely problematic (Table 11). Small firms also were more likely to indicate that end checking, case hardening, sticker stain, and setting pitch were problematic relative to larger firms. As noted earlier, small firms tended to make their own stickers and often did not take advantage of advanced sticker designs. Across most other issues, ratings were similar regardless of firm size. For large firms, discoloration or staining (e.g., sap stain) was rated as very or extremely problematic by 33.3 percent of respondents, which was the highest rated issue for large firms.

Table 11.How problematic are the following kiln-dried lumber quality issues to you?

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