Final answer:
The first component to energize on a call for heat in an induced-draft gas furnace is the compressor. It increases the temperature and pressure of the gas, forcing it into the condenser coils and transferring heat to the room.
Step-by-step explanation:
In an induced-draft gas furnace, the first component to energize on a call for heat is the compressor. The compressor increases the temperature and pressure of the gas and forces it into the condenser coils inside the heated space. This allows heat transfer from the gas to the room as the gas condenses into a liquid, warming up the room.