During a remodel, we took out a wall where one of the emergency shutoff switches was located, the other being at the boiler. We have a natural gas system.

I have the switch temporarily nailed up on the nearest wall, which was by the side door/kitchen entrance, but would like to know if there are any particular rules that govern where it needs to be permanently located.

The emergency switch cannot be located in the same room as the appliance but if the boiler is in a basement, then a switch at the head of the basement steps is okay. The idea is: if there is an emergency necessitating that the appliance be shut down, you don't want to have to enter that room where the appliance is located to disable it.

by my code there is no emergency switch needed for natural gas.
carbon monoxide detectors on every floor are more to the point.

I have never heard of one being in a residence, but the primary rule for its location is that it be accessible, usually as someone is leaving the building.

around here red emergency switch (oil burner only) must be in a prominant location at the front entrance of the residence. the idea is that when the fire department arrives they know where to look. it also wants to be mounted at shoulder level so it won't be confused with a regular electric switch.
but, as i said, gas equipment does not require an emergency switch.

What is there about an oil burner that NEEDS an emergency switch?