I'm looking to replace my 16 yr old 4 ton Amana gas pac with either a dual fuel HP or another gas pac (either case Trane or Carrier). Will also install aprilaire zone system for my 2floors plus half basement home. Reliability in the heating mode is the most important criteria - lose heat, you're in trouble. Lose AC, you're just uncomfortable. It would seem to me that a simple gas pac is much less likely to fail than any heat pump based system. Is this right? Can a dual fuel unit switch automatically to a gas heat only mode? And if so, is their gas heating capacity enough to do the job?