Conventional lumber drying is carried out by forcing hot air to flow across a pile of lumber layers separated by wood strips. The airflow provides the heat required to warm up the lumber and produce the moisture evaporation and, in theory, the difference in temperature at each side of the load can be used to estimate the evaporation rate. The main problem with this approach is that typical temperature sensors that are installed in conventional kilns are not accurate enough to measure the temperature drop across the load during periods of low evaporation. In this paper, a new sensor to measure the temperature drop across the load is proposed and tested in three experimental drying runs of 2" X 6" spruce-pine lumber. The results demonstrate that after calibration, the temperature drop across the load can be used to determine drying curves in conventional lumber drying. In the particular case of this study, calibration was performed by multiplying the experimental temperature drop across the load by a constant factor, which was adjusted by identifying the correction factor that best simulated the experimental green moisture content of the three lumber charges.