For an 80,000 BTU gas furnace with a 3-ton cooling system, what size copper conductor is normally used?

The correct choice is based on the current-carrying capacity and application requirements for the system in question. An 80,000 BTU gas furnace typically has a significant electrical demand due to the blower motor and any ignition systems. The associated cooling system with a capacity of 3 tons also contributes to the overall electrical load.

In this scenario, a size of 12 - 14 AWG copper conductor is usually recommended. This range ensures that the wire can handle the expected current without overheating and maintains efficiency and safety. The 12 AWG wire has a higher current rating compared to 14 AWG, providing some flexibility for potential load increases or longer distances without voltage drop.

The smaller wire sizes (14 - 16 AWG and 16 - 18 AWG) would not provide sufficient capacity for the electrical demands of both the gas furnace and the cooling system, making them inadequate choices. On the other hand, while 10 - 12 AWG may seem capable, it may be unnecessary for this specific application, as it is often used for larger systems or longer runs requiring higher currents.

Selecting the appropriate wire gauge ensures operational safety and reliability, significantly impacting the overall performance of the HVAC system.