During the first seven to ten days of life chicks are unable to maintain homeothermy, thus providing supplemental heat is critical to their livability and performance. Radiant heaters are the preferred method of providing heat during brooding because they provide a range of thermal comfort options for chicks. Infrared thermography is often used to assess the heat distribution created at the litter surface by radiant heaters. The resulting images provide a good qualitative assessment of heat distribution but do not provide any quantifiable metrics through which to compare the radiant output of heaters. Data acquisition systems were developed to measure the radiant flux emitted by six 11.72 kW radiant heaters and to determine radiant flux ranges preferred by broiler chicks during the first week of brooding. Results showed the radiant output was influenced by heater elevation above the litter and differed between manufacturers. 21 – 41% of the energy available the heaters was emitted to the litter as radiant heat. Chicks exhibited a decreasing preference for radiant flux with age. Maximum preferred radiant flux decreased from 387.0 W·m-2 at day 1 to 248.3 W·m-2 at day 8, while the minimum preferred radiant flux decreased from 61.2 W·m-2 at day 1 to 7.65 W·m-2 at day 8. Net usable area (NUA), or the total floor area within the range of radiant fluxes preferred by chicks, was calculated for each heater. Mean NUA by heater ranged from 45.34 (SE = 3.35 m2) to 21.75 (SE = 1.98 m2). Mean NUA significantly increased with heater mounting elevation (P < 0.0001). Results indicate that radiant heaters from different manufacturers with the same power output do not necessarily produce the same radiant distribution and that the maximum preferred radiant fluxes by chicks may not be realized at manufacturer specified heater mounting elevations.