I answered this a few minutes ago at EDAboard:
"What is an INamp?? Is it an instrumentation amplifier IC like an AD620? It is not needed in a simple vaping device.
A simple piece of nichrome heating wire with DC in it will work. Simple electricity, not electronics. The battery charger, the display that shows the battery charge level and low voltage disconnect use some electronics.
I laugh each time I see a teen killing himself by disappearing into a huge cloud of vapour."