HERS Combustion Safety Principles 2 — Questions and Answers
Question 1: What is the primary purpose of a combustion air opening in a mechanical room?
- To exhaust flue gases to the outside
- To provide adequate oxygen for complete combustion (Correct answer)
- To reduce indoor humidity levels
- To supply makeup air for kitchen exhaust fans
Correct answer: To provide adequate oxygen for complete combustion
Combustion air openings supply sufficient oxygen to support complete combustion and prevent CO production from fuel-fired appliances.
Question 2: During a worst-case depressurization test, which combination of conditions is typically induced?
- All windows open, all fans off
- All exhaust fans on, fireplace damper open, supply fans off (Correct answer)
- Only the furnace blower running
- HVAC system on heating mode with all doors closed
Correct answer: All exhaust fans on, fireplace damper open, supply fans off
Worst-case depressurization maximizes negative pressure by operating all exhaust devices and opening fireplace dampers simultaneously.
Question 3: A gas water heater located in a garage must have its burner and pilot elevated at least how high above the floor?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
Garage-installed water heaters must have ignition sources elevated at least 18 inches above the floor to avoid igniting gasoline vapors that pool at floor level.
Question 4: Which test instrument is used to measure carbon monoxide concentration in appliance flue gases?
- Manometer
- Combustion analyzer (Correct answer)
- Blower door
- Infrared camera
Correct answer: Combustion analyzer
A combustion analyzer measures CO, CO2, O2, and flue gas temperature to assess combustion efficiency and safety.
Question 5: What does a yellow or orange burner flame on a natural gas appliance most likely indicate?
- Efficient complete combustion
- Insufficient combustion air causing incomplete combustion (Correct answer)
- Excess combustion air diluting the flame
- High gas pressure at the appliance
Correct answer: Insufficient combustion air causing incomplete combustion
Yellow or orange flames indicate incomplete combustion from insufficient air, which can produce dangerous levels of carbon monoxide.
Question 6: What is the term for the phenomenon where combustion appliance exhaust is pulled back into the living space through the flue?
- Backdrafting (Correct answer)
- Short-cycling
- Flue recirculation
- Stack effect reversal
Correct answer: Backdrafting
Backdrafting occurs when negative house pressure or adverse weather conditions reverse the intended upward flow of combustion gases through the flue.
Question 7: Which RESNET standard governs combustion safety testing procedures for HERS raters?
- RESNET/ICC 301
- RESNET/ACCA 310
- RESNET/ICC 380 (Correct answer)
- RESNET 55
Correct answer: RESNET/ICC 380
RESNET/ICC 380 establishes standard test methods for building enclosures, including combustion safety diagnostics performed by HERS raters.
HERS Combustion Safety Principles 2
What is the primary purpose of a combustion air opening in a mechanical room?