Abstract <p>The temperature of condensed phase particles formed during flame combustion of peat from Kirov oblast in a BKZ-210-140F boiler was studied using a pyrometric method. The authors elaborated an experimental-and-calculation procedure for pyrometry of the furnace enabling determination of the temperature of condensed phase particles (of coke and ash) in the gas phase transparency band. The measurements were taken using Raynger R3I 2MSC and Kelvin 2300 PLTs pyrometers having radiation receivers operating at a wavelength of 1.6 µm and in a spectral range from 1.0 to 1.6 µm, respectively. Dependences are obtained of the temperatures measured at different heights from the boiler furnace bottom to the measurement point (hereinafter referred to the boiler furnace height) (<i>H</i> = 9, 14, and 16 m), on the emissivity set on the pyrometers in the range from 0.1 to 1.0. Spectral and integral radiative energy flux densities sensed by the pyrometers were calculated. Brightness temperatures observed during peat combustion were determined. The software package developed by the authors was used for computational studies of the condensed phase emissivity as a function of the specified temperature considering the fuel burnout along the furnace height by solving the radiative transfer equation for a multicomponent radiating, absorbing, and scattering medium. The intersection of the experimental and predicted functions gave the emissivity and true temperatures of the condensed phase particles. According the measurements taken by the Raynger pyrometer, the particle temperature in the flame root part (<i>H</i> = 9 m) is equal to 1453 K; it is 1226 K in the flame middle part (<i>H</i> = 14 m) and 1334 K in the flame tail part (<i>H</i> = 16 m). For the Kelvin pyrometer, these temperatures were 1471, 1265, and 1343 K, respectively. The obtained particle temperatures enabled us to assess the risk of melting of the mineral part of the fuel and slagging of the furnace.</p>