In the US swine industry, one of the largest economic and production losses is pre-weaning mortality (PWM). The vast differences in thermal needs of the sow and piglet create a complex environment that meets this requirement. The objectives of this study was to extend the Effective Environment Temperature (EET) calculation for newborn piglets to encompass the end of lactation at 21 days of age and compare the EET under a Semi-Enclosed Heated Microclimate (SEHM) and a Heat Lamp (HL). Twelve SEHMS were randomly placed in two farrowing rooms and data was collected over six turns from Thermal Environment Sensor Arrays (TESAs) installed under all SEHMs and selected HLs. Each SEHM had individualized heat output control via a dry-bulb temperature feedback and a commercial data acquisition and control (DAQC) system. Utilizing data from Midwest Plan Service on pig dimensions and maximum tissue resistance equations, the diameter and tissue resistance were estimated for piglets from 7 to 21 days of age. Data were analyzed for farrowing turns 2 through 6 as the SEHM was updated following the first turn. On average the SEHM averaged a higher EET compared to the HL (30.5°C and 27.0°C, respectively). The daily average comparison across an eighteen day lactation showed that the SEHM had a consistently higher EET and was closer to the ideal range of EET for piglets through day 7. Future development of the ideal EET range for piglets beyond day 7 of age is needed.