Adding smokes and ROR detectors to existing alarm system

["Dave A" <Dave.Alverson@xxxxxxxxx>]

I purchased a new home about 18 months ago that included a GE Networx
NX6V2 security system.  The home also has the typical interconnected
120V smoke alarms required by code.  However, the security system did
not include any smoke or heat detectors.  I would like to add some new
smoke and ROR heat sensors to the security system so that I can have
monitored fire detection.  I have done some research on my own, and I
understand that the NEC requires FPL 18AWG (minimum) rated fire wire
for the smoke and heat sensors.  I also understand that all common
components (i.e. keypad, sounder, power supply) must use fire rated
wiring.  The system currently installed does not use any fire rated
wiring.  So I will need to replace some of the existing runs with fire
rated wire.  My question is this, do I also need to use 18AWG wire for
the keypad runs?  I have seen several vendors selling 22/4 AWG FPLR
rated fire wire.  Would this be approved by NEC code if used only for
the keypads?  The 22/4 is considerably cheaper than 18/4 and my runs
would be short (no more than about 30 ft each.)

Also, I would like to include a combo 190 deg heat and ROR sensor in
the attic.  Any advice on the best placement for this?  I would assume
centrally located near the highest point inside the attic, but I would
appreciate any constructive advice.

Thanks,
Dave A.