FC FC Combustion & Fuel Systems 2

Question 1

What instrument is used to measure gas manifold pressure on a furnace?

Accepted Answer

Manometer

Answer

A manometer (or magnahelic gauge) measures the low pressure in inches of water column at the furnace manifold.

Question 2

What is the typical supply gas pressure (upstream of the gas valve) for a natural gas furnace?

Accepted Answer

5–7 inches W.C.

Answer

Natural gas utility supply pressure is typically 5–7 inches W.C. at the meter and furnace inlet.

Question 3

A cracked heat exchanger is most likely to allow which dangerous gas to enter the living space?

Accepted Answer

Carbon monoxide

Answer

A cracked heat exchanger allows combustion byproducts including deadly carbon monoxide to leak into the circulating air.

Question 4

What is the primary purpose of a draft inducer motor on a high-efficiency furnace?

Accepted Answer

To pull combustion gases through the heat exchanger and exhaust them outdoors

Answer

The draft inducer creates a negative pressure to draw flue gases through the heat exchanger and out the venting system.

Question 5

Which type of ignition system uses a resistance element heated to approximately 1,800°F to ignite the gas?

Accepted Answer

Hot surface igniter

Answer

A hot surface igniter (HSI) uses silicon carbide or silicon nitride that glows red-hot to directly ignite the gas-air mixture.

(FC) Furnace Installation and Maintenance Certification Practice Test