Gas Packs are considered the “all in one” HVAC system. This system combines your gas heating and electrical air conditioning all outside the home with the ductwork running beneath the home. The thermostat is the only portion of the unit that resides inside the home. The Gas Pack system is considered the easiest to install of all types of HVAC systems. Gas Packs use Natural Gas for the heat source, but can be converted to accept liquid propane like most gas furnaces..