Enviro+ schematics for mics6814 heater and ADC connection please

Enviro+ is great but I want to understand how each sensor works in detail.
Can we please get some information how the mics6814 heaters are wired and how the sensor outputs are connected to the ADC? I am pretty sure you are not strictly following the 6814’s datasheet here (presumably because you are feeding it from 3.3V? and presume the 1015 ADC can handle the range?