Gas and Oil Home Heating Furnaces - Boiler wiring

This weekend I had my plumber install a new New Yorker power vent boiler. As part of the deal I am doing the electric wiring. As I understand the code, I must install a emergency shutoff switch at the bottom of the basement stairs. If this is wrong please let me know. I am not sure if I must use rigid conduit from the overhead temp cutoff to the boiler, of if flex is ok.
Also, I need to add another power vent boiler in the same location, how close can the vents be to each other on the outside of the house?

It depends on the electrical code what type of wiring you can use. I prefer conduit, but that's a personal preference.

If so, it is doubly important that code be followed if it is.

is different in all areas. call local building inspector for final verdict.