A method for determining temperature information for a plurality of tubes in a furnace, the method comprising: capturing one or more digital images of an interior area of the furnace wherein the one or more digital images comprises pixel data associated with a subset of the plurality of tubes positioned inside the furnace; identifying a plurality of imaged tubes in the subset of the plurality of tubes in the one or more digital images, the plurality of tubes comprising the imaged tubes and non-imaged tubes, the imaged tubes detected in the one or more digital images, the non-imaged tubes not detected in any of the one or more digital images; processing a portion of the pixel data associated with the plurality of imaged tubes to obtain a value representing a measure of central tendency for at least a subset of the plurality of imaged tubes in the one or more digital images; processing the value representing the measure of central tendency for at least the subset of the plurality of imaged tubes to obtain temperature information for at least the subset of the plurality of imaged tubes; withdrawing an effluent from each of the plurality of tubes; collecting the effluent withdrawn from each of the plurality of tubes in a plurality of secondary collection headers, each of the plurality of secondary collection headers operatively connected to a respective group of multiple groups of the plurality of tubes, the effluent collected in each secondary collection header forming a respective combined effluent in each secondary collection header; passing the effluent collected in each respective secondary collection header to a primary collection header; measuring a value relatable to a temperature of the combined effluent in one or more secondary collection headers of the plurality of secondary collection headers; and processing the value representing the measure of central tendency for at least the subset of the plurality of imaged tubes and the value relatable to the temperature of the combined effluent in the one or more secondary collection headers to obtain temperature information for at least a subset of the non-imaged tubes of the plurality of tubes. capturing one or more digital images of an interior area of the furnace wherein the one or more digital images comprises pixel data associated with a subset of the plurality of tubes positioned inside the furnace; identifying a plurality of imaged tubes in the subset of the plurality of tubes in the one or more digital images, the plurality of tubes comprising the imaged tubes and non-imaged tubes, the imaged tubes detected in the one or more digital images, the non-imaged tubes not detected in any of the one or more digital images; processing a portion of the pixel data associated with the plurality of imaged tubes to obtain a value representing a measure of central tendency for at least a subset of the plurality of imaged tubes in the one or more digital images; processing the value representing the measure of central tendency for at least the subset of the plurality of imaged tubes to obtain temperature information for at least the subset of the plurality of imaged tubes; withdrawing an effluent from each of the plurality of tubes; collecting the effluent withdrawn from each of the plurality of tubes in a plurality of secondary collection headers, each of the plurality of secondary collection headers operatively connected to a respective group of multiple groups of the plurality of tubes, the effluent collected in each secondary collection header forming a respective combined effluent in each secondary collection header; passing the effluent collected in each respective secondary collection header to a primary collection header; measuring a value relatable to a temperature of the combined effluent in one or more secondary collection headers of the plurality of secondary collection headers; and processing the value representing the measure of central tendency for at least the subset of the plurality of imaged tubes and the value relatable to the temperature of the combined effluent in the one or more secondary collection headers to obtain temperature information for at least a subset of the non-imaged tubes of the plurality of tubes.