gas sample acquisition apparatus 20 includes a housing 24 the housing 24 is made to comply with nema standards and is insulated the housing 24 is attached to the exhaust stack 22 by a tubular connector 26 since the tubular probe assembly is mounted on the exhaust stack access to the probe and therefore maintenance of the probe assembly is difficult and time consuming it is desirable that the probe assembly be as reliable and maintenance free as possible the gas sample acquisition apparatus 20 also includes a probe assembly 40 mounted in the housing 24 components of the probe assembly 40 are tubular the probe assembly 40 includes an inlet or probe tip 42 that is in fluid communication with the flue gas stream in the exhaust stack 22 the probe tip 42 is connected to an inertial filter 44 of the probe assembly 40 the inertial filter 44 is attached to a generally u shaped stainless steel return pipe 46 the stainless steel return pipe 46 is attached to a venturi flow meter 48 the venturi flow meter 48 is connected to an outlet or eductor 62 that is open to the flue gas flow the temperature of the gas sample within the components of the probe assembly 40 located in the housing 24 is maintained via a block or jacket heater 64 the probe tip 42 extends into the exhaust stack 22 through flexible thermal insulation 82 the probe tip 42 draws a sample from the exhaust flue gas flow the gas sample is transported into the inertial filter 44 the gas sample leaves the inertial filter 44 via the stainless steel return pipe 46 the gas sample then passes through the venturi flow meter.