NATE Gas Heating Practice Exam

Which sequence of operations is typical for a high efficiency condensing furnace?

1. Induced draft blower runs, ignitor heats, gas valve opens, burner lights

2. Ignitor heats up, gas valve opens, induced draft blower starts immediately

3. Induced draft blower runs, ignitor heats up, gas valve opens, burner lights, and flame sensor monitors

4. Induced draft blower becomes inactive while the burner operates

The correct answer is: Induced draft blower runs, ignitor heats up, gas valve opens, burner lights, and flame sensor monitors

The sequence of operations for a high-efficiency condensing furnace typically involves multiple steps that ensure proper operation and safety. The correct sequence begins with the induced draft blower running first, which is crucial for creating the negative pressure needed to vent exhaust gases safely out of the furnace and up the flue. This step also ensures that fresh air is being pulled into the combustion chamber for proper combustion. Next, the ignitor heats up, preparing for the ignition of the gas. This heating period allows the ignitor to reach the necessary temperature to ignite the gas efficiently and safely. Following this, the gas valve opens, allowing the flow of gas to the burner. The burner lights once the gas is present, leading to combustion. Finally, the flame sensor plays a vital role by continuously monitoring the presence of a flame during operation. If the flame goes out for any reason, this safety feature ensures that the gas supply is interrupted, preventing potential hazards such as gas leaks or explosions. This sequence incorporates essential safety and operational features that are specific to high-efficiency condensing furnaces, which prioritize efficient combustion and safe venting of exhaust gases.