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

The heat exchanger is a sealed metal chamber that transfers heat from hot combustion gases to the circulating supply air while keeping them completely separated.

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

A tracer gas test introduces a detectable gas (such as nitrogen with a halogen additive) into the combustion chamber to identify cracks by sensing tracer gas in the air stream.

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

Cracks in the heat exchanger allow combustion gases with elevated CO to enter the supply airstream, especially when draft pressure is favorable.

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

Chronically restricted airflow (dirty filters, closed registers) causes the heat exchanger to overheat repeatedly, leading to metal fatigue and cracking.

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

When the blower starts, air pressure changes can cause a cracked heat exchanger to deflect and disturb the burner flames, visible as flame rollout or flickering.

(FC) Furnace Installation and Maintenance Certification Practice Test

(FC) Furnace Installation and Maintenance Certification Practice Test

FC FC Heat Exchangers & Blower Systems