But this is Florida, furnaces only get used for about six weeks in the dead of winter.
I don’t know much about it, either - but I do know plants inhale CO2, and exhalt O2 - so that underground bunker would become an oxygen-rich environment pretty darn quick, unless he had a vent system.
You would get high on oxygen just going down there.
Like they said it was pretty elaborate setup, state of the art