FC FC Heat Exchangers & Blower Systems

Question 1

What is the primary function of the heat exchanger in a gas furnace?

Accepted Answer

To transfer heat from combustion gases to the circulating air without allowing gases to mix

Answer

To filter combustion gases

Answer

To store heat between cycles

Answer

To regulate gas pressure

Question 2

Which test method uses a chemical tracer gas introduced into the combustion side to detect heat exchanger cracks?

Accepted Answer

Tracer gas leak test (e.g., nitrogen with halide detector)

Answer

Combustion analysis

Answer

CO ambient test

Answer

Thermal imaging only

Question 3

What happens to supply air CO levels when a cracked heat exchanger is combined with a high-temperature operating condition?

Accepted Answer

CO levels in the supply air increase significantly due to combustion gas infiltration

Answer

CO levels remain unchanged

Answer

CO levels decrease as combustion improves

Answer

CO levels vary only with outdoor temperature

Question 4

What is the most common cause of premature heat exchanger failure in residential furnaces?

Accepted Answer

Restricted airflow causing repeated thermal stress from overheating cycles

Answer

Oversized gas valve

Answer

Hard water condensate

Answer

Excessive flue gas velocity

Question 5

Which inspection technique is commonly used by technicians to visually check for heat exchanger cracks during operation?

Accepted Answer

Observe the burner flame for movement or disturbance when the blower turns on

Answer

Shine a bright flashlight inside the heat exchanger only

Answer

Use a borescope camera through the flue outlet

Answer

Measure flue gas temperature with a thermocouple

Question 6

A condensing furnace has a primary and secondary heat exchanger. What is the role of the secondary heat exchanger?

Accepted Answer

To extract additional latent heat from water vapor in the flue gas, condensing it to liquid

Answer

To preheat the combustion air

Answer

To cool the flue gas before venting

Answer

To filter particulates from the flue gas