Rock the Gas Heat ESCO Exam 2026 – Fire Up Your Future in HVAC!

A A pressure sensor is not typically used to cycle the fan on during the heating cycle in modern gas furnaces. Pressure sensors are commonly used to monitor gas pressure in the appliance but not to control the fan.

B: Temperature differential is not used to cycle the fan on during the heating cycle in most modern gas furnaces. This term refers to the difference in temperature between two points and is not a method of fan control.

D: A voltage regulator is not used to cycle the fan on during the heating cycle in most modern gas furnaces. Voltage regulators are used to control the output voltage of a circuit and would not be applicable to controlling fan cycles.

A time delay relay is the method commonly used to cycle the fan on during the heating cycle in most modern gas furnaces. It operates by allowing a set amount of time to pass before activating the fan, preventing it from starting up immediately and causing cold air to blow out of the vents. This delay also gives the furnace enough time to heat up before the fan comes on, ensuring that warm air is circulated throughout the home. Additionally, time delay relays are more energy-efficient compared to other methods such as continuous fan operation. Therefore, C is the correct answer.