NATE Gas Heating

Question 1

What is the primary safety device that shuts off the gas valve if the pilot flame is extinguished on a standing pilot furnace?

Accepted Answer

Thermocouple

Answer

The thermocouple generates a small millivolt signal that holds the gas valve open; when the pilot goes out the signal drops and the valve closes.

Question 2

What is the purpose of the heat exchanger in a gas furnace?

Accepted Answer

Transfer heat from combustion gases to the circulating air without mixing them

Answer

The heat exchanger keeps combustion products separated from conditioned air while allowing heat transfer through the metal walls.

Question 3

What component in an induced-draft furnace proves that combustion airflow is established before the gas valve opens?

Accepted Answer

Pressure switch

Answer

The pressure switch senses negative pressure created by the inducer motor to confirm draft is established before allowing ignition.

Question 4

What type of ignition system uses a glowing ceramic element to ignite the gas burners in modern furnaces?

Accepted Answer

Hot surface igniter (HSI)

Answer

Hot surface igniters heat to approximately 1800–2500°F using electricity to ignite the gas burner, replacing standing pilots.

Question 5

What is the function of the rollout switch on a gas furnace?

Accepted Answer

Detect flame rollout and shut down the furnace if heat exceeds safe limits near the burner compartment

Answer

Rollout switches are manual-reset thermal devices that trip if flames exit the burner compartment, indicating a serious combustion problem.

NATE - North American Technician Excellence Practice Test