Please post complete circuit diagram.
For these sensors you can generally get much better results (stability, resolution) by using the internal 1.1V reference.
Same project here.
https://forum.arduino.cc/index.php?topic=547471.0
OP did already have a cross-post warning.
Leo..
Which Arduino, where does the heatpad power come from?
9V block batteries are intended for smoke alarms, and will run an Arduino alone for just a few minutes.
If it has to power anything else, expect rapid failures.
Threads merged.