Re: Area surrounding chimney as raceway
This is a common practice when trying to fish from basement to attic.
If I use 12/2 NM as an example, 12 AWG is rated 30 amps in 310.16 (forget about 240.4(D) for now) now apply the temperature correction factors from 310.16 to 30 amps and you will find you can run the 12 AWG through ambient temperatures of 132 to 140F and still end up with an ampacity of 21.3 amps.
30 amps x.71 temperature correction factor = 21.3 amps at 132 to 140F
You could go further if you use 240.4(B) which allows the use of the next higher standard overcurrent device rating.
30 amps x .58 temperature correction factor = 17.4 amps at 141 to 158F and you could still use a 20 amp breaker.
I would not think the temperature around a chimney would be higher than 158F.
210.4 Protection of Conductors.
(B) Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.
Most systems work best if they are kept simple rather than made complicated; therefore simplicity should be a key goal in design and unnecessary complexity should be avoided.