"The AD8494/AD8495/AD8496/AD8497 allow a wide variety of supply voltages. With a 5 V single supply, the 5 mV/°C output allows the devices to cover nearly 1000 degrees of a thermo-couple’s temperature range."
http://www.analog.com/static/imported-files/data_sheets/AD8494_8495_8496_8497.pdf
How are you powering the AD8495?
The AD849x achieves a linearity error of less than ±2°C, within the specified operating ranges listed in Table 7.
AD8495 K ±2°C 0°C to 50°C ?25°C to +400°C
For temperature ranges outside those listed in Table 7 or for instructions on how to correct for thermocouple nonlinearity error with software, see the AN-1087 Application Note for additional details.