NATE Gas Heating 2

Question 1

What is the AFUE rating and what does it measure for a gas furnace?

Accepted Answer

Annual Fuel Utilization Efficiency; measures what percentage of fuel energy is converted to heat

Answer

Airflow Factor Under Extreme conditions

Answer

Average Furnace Unit Efficiency; measures BTU output

Answer

Annual Flue Utilization Effectiveness

Question 2

What type of venting is required for a 96% AFUE condensing gas furnace?

Accepted Answer

PVC plastic pipe for both flue and combustion air

Answer

Type B double-wall vent

Answer

Category IV stainless steel vent

Answer

Masonry chimney with liner

Question 3

What does the flame sensor do in a modern electronic ignition furnace?

Accepted Answer

Passes a small DC current through the flame to prove ignition and keep the gas valve open

Answer

Measures combustion air temperature

Answer

Controls burner gas pressure

Answer

Monitors heat exchanger temperature

Question 4

What is a condensate drain trap used for on a high-efficiency furnace?

Accepted Answer

Prevent flue gases from backing up through the condensate drain while allowing water to drain freely

Answer

Trap combustion gases before they exit

Answer

Filter particulates from the condensate water

Answer

Reduce drain line vibration

Question 5

What color should the burner flame be on a properly adjusted natural gas furnace?

Accepted Answer

Mostly blue with slight yellow tips

Answer

Yellow/orange with tips

Answer

Pure white

Answer

Red/orange

Question 6

A furnace high-limit switch trips repeatedly. What is the most common cause?

Accepted Answer

Dirty air filter or restricted airflow causing the heat exchanger to overheat

Answer

Gas valve is stuck open

Answer

Faulty thermostat

Answer

Low gas pressure