HERS Diagnostic and Field Testing 3 — Questions and Answers
Question 1: What is the primary purpose of performing a combustion safety test during a HERS rating?
- To verify HVAC system efficiency ratings
- To identify carbon monoxide spillage or backdrafting risks in combustion appliances (Correct answer)
- To measure natural gas consumption
- To confirm adequate combustion air supply for the furnace
Correct answer: To identify carbon monoxide spillage or backdrafting risks in combustion appliances
Combustion safety testing identifies dangerous conditions where combustion byproducts such as carbon monoxide can spill back into living spaces from appliances like furnaces and water heaters.
Question 2: Which test condition is considered 'worst case' for combustion safety testing of atmospherically vented appliances?
- All windows open, no exhaust fans running
- All doors open, supply fans running
- All exhaust fans on, interior doors closed to maximize depressurization (Correct answer)
- Blower door at 50 Pascals, all registers open
Correct answer: All exhaust fans on, interior doors closed to maximize depressurization
Worst-case depressurization with all exhaust fans operating and interior doors closed creates the greatest negative pressure that could cause backdrafting.
Question 3: When using a calibrated manometer to measure pressure difference across the building envelope, the reference port (Channel B) should be placed:
- Inside the house near the blower door
- Outside in an undisturbed location (Correct answer)
- In the attic space
- Adjacent to the return air plenum
Correct answer: Outside in an undisturbed location
The reference port must be placed outdoors in a sheltered, undisturbed location to accurately measure the pressure difference between inside and outside.
Question 4: A HERS rater finds a CO reading of 35 ppm in the flue gases of a natural draft water heater. What is the appropriate action?
- Record the value and continue rating — it is within normal range
- Immediately notify the homeowner and recommend appliance service before occupancy (Correct answer)
- Retest at a different pressure to confirm the reading
- Flag it only if the reading exceeds 100 ppm
Correct answer: Immediately notify the homeowner and recommend appliance service before occupancy
Any CO detected during combustion safety testing should be reported to the homeowner and serviced before occupancy, as CO poses an immediate health and safety risk.
Question 5: What does 'spillage' mean in the context of combustion appliance zone (CAZ) testing?
- Gas leaking from supply lines
- Combustion byproducts escaping from the draft hood into the living space (Correct answer)
- Excess condensate draining from high-efficiency equipment
- Air infiltrating through gaps around the flue pipe
Correct answer: Combustion byproducts escaping from the draft hood into the living space
Spillage occurs when combustion gases escape through the draft hood or diverter of an atmospherically vented appliance into the surrounding zone instead of exhausting through the flue.
Question 6: During a pressure diagnostics test, a rater measures -3 Pascals in a bedroom with the door closed and the HVAC system running. This indicates:
- Excessive supply airflow to the bedroom relative to return air capacity (Correct answer)
- Adequate air balancing in the bedroom
- The bedroom window is leaking
- Return air is located in the bedroom
Correct answer: Excessive supply airflow to the bedroom relative to return air capacity
A negative pressure in a bedroom with the door closed indicates more supply air is being delivered than can return, causing the room to be pressurized relative to... actually -3 Pa means the room is slightly negative, indicating insufficient supply or excessive return bypass — but typically a negative room with door closed means the return is pulling more than the supply delivers, suggesting the system is pulling from that room.
Question 7: Which instrument is specifically used to measure the airflow of individual supply registers during HVAC diagnostics?
- Blower door
- Duct blaster
- Flow hood (balancing hood) (Correct answer)
- Anemometer
Correct answer: Flow hood (balancing hood)
A flow hood, or balancing hood, is placed directly over a supply or return register to measure the airflow in CFM at that specific outlet.
HERS Diagnostic and Field Testing 3
What is the primary purpose of performing a combustion safety test during a HERS rating?