FC FC Combustion & Fuel Systems

Question 1

What is the stoichiometric air-to-fuel ratio for natural gas combustion?

Accepted Answer

15.4:1

Answer

Natural gas requires approximately 15.4 parts air to 1 part fuel for complete stoichiometric combustion.

Question 2

Which color of a burner flame indicates incomplete combustion?

Accepted Answer

Yellow or orange

Answer

A yellow or orange flame indicates incomplete combustion due to insufficient air or a clogged burner.

Question 3

What device on a gas furnace controls the flow of gas to the main burner?

Accepted Answer

Gas valve

Answer

The gas valve opens and closes to control gas flow to the main burner based on thermostat demand.

Question 4

What is the purpose of a burner orifice in a gas furnace?

Accepted Answer

To meter the correct amount of gas into the burner

Answer

The orifice spud meters the precise amount of gas needed to produce the correct BTU output at the burner.

Question 5

When converting a furnace from natural gas to propane (LP), what must be replaced?

Accepted Answer

The orifice spud and pressure regulator spring

Answer

Propane has higher BTU content and different pressure requirements, so orifices must be downsized and the regulator spring changed.

(FC) Furnace Installation and Maintenance Certification Practice Test