DirectlyFlammability aside, directly using Butane/Propane is out of the question due to the pressure needed (145-200psi) to liquefy it and the fact that the immersion tank needs access for the miners so not only big but also needs a hatch. Might as well use a Flourinert that is liquid with a boiling point of say 140F and condense the vapor
back into the tanks using water from a dry cooler. That is how the BitFury farms work.
ref https://liquidstack.com/2-phase-immersion-cooling