I've heard of the switch at the top of the stairs, but it is not an NEC requirement. Could be it is a local requirement or is in the mechanical code. Keep in mind that the switch at the top of the stairs probably would not qualify as the disconnecting means for the furnace since it will likely be out of sight (see the definitions in chapter 1). If the circuit breaker for the furnace is out of sight, you would need a permanently installed lockout attachment (opinion/interpretation) at the circuit breaker or another switch at the furnace to use as a disconnecting means.
Outside the closet seems like a logical place for the switch. You could tell if you left the light on without opening the door.
Tom
[This message has been edited by Tom (edited 10-17-2002).]
