Diagnostic and Field Testing Flashcards

When performing a duct leakage test, which metric is used to express total duct leakage in RESNET standards?

Answer: CFM25 total

RESNET standards express total duct leakage as CFM25 total, meaning airflow in cubic feet per minute at 25 Pascals of pressure.

A HERS rater measures duct leakage to outside at 52 CFM25 on a 1,800 sq ft home. What is the duct leakage to outside as a percentage of conditioned floor area?

Answer: 2.9%

52 CFM25 divided by 1,800 sq ft equals approximately 2.9%, which is the standard way to normalize duct leakage to outside.

During blower door testing, what does a high inside-out pressure differential (house more negative than outside) indicate?

Answer: The fan is depressurizing the house as expected

When the blower door fan exhausts air, it depressurizes the house, making interior pressure more negative than outside — this is the intended test condition.

What is the purpose of a 'duct blaster' test conducted with the air handler fan OFF?

Answer: To isolate and measure duct system leakage independently from the air handler

Testing with the air handler off isolates duct system leakage from equipment leakage and measures only the ductwork integrity.

Which condition would most likely cause an artificially LOW blower door reading during envelope testing?

Answer: An open window on the leeward side

An open window allows air to flow freely, reducing the pressure differential and causing the blower door to read less leakage than actually exists.

In a HERS duct leakage test, 'leakage to outside' differs from 'total leakage' because:

Answer: Leakage to outside only counts ducts outside conditioned space

Leakage to outside only counts duct leakage that goes to unconditioned spaces (attic, crawlspace, garage), while total leakage includes all duct system leakage.

A rater is testing a home with a sealed attic (unvented). When measuring duct leakage to outside, how should ducts located entirely within this sealed attic be treated?

Answer: They do NOT count as outside leakage since the attic is within the conditioned envelope

Ducts in a sealed, unvented attic that is part of the conditioned space are considered inside the thermal envelope, so their leakage does not count as leakage to outside.

What is the primary purpose of performing a combustion safety test during a HERS rating?

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.

Which test condition is considered 'worst case' for combustion safety testing of atmospherically vented appliances?

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.

When using a calibrated manometer to measure pressure difference across the building envelope, the reference port (Channel B) should be placed:

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.

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?

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.

What does 'spillage' mean in the context of combustion appliance zone (CAZ) testing?

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.

During a pressure diagnostics test, a rater measures -3 Pascals in a bedroom with the door closed and the HVAC system running. This indicates:

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.

Which instrument is specifically used to measure the airflow of individual supply registers during HVAC diagnostics?

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.

What pressure standard does RESNET use for normalizing envelope air leakage in a blower door test?

Answer: 50 Pascals

RESNET and most U.S. energy codes use 50 Pascals as the reference pressure for blower door testing and reporting air leakage (ACH50 or CFM50).

A home tests at 1,850 CFM50 and has a volume of 12,000 cubic feet. What is the ACH50 value?

Answer: 9.25 ACH50

ACH50 = (CFM50 × 60) / volume = (1,850 × 60) / 12,000 = 111,000 / 12,000 = 9.25 ACH50.

In HERS field testing, what does 'verified' mean in the context of duct leakage testing?

Answer: A third-party certified rater performed and documented the measured test result on-site

Verified testing means a certified HERS rater physically performed and documented the measurement on-site, as opposed to an assumed or estimated value.

When a HERS rater tests a multi-story home, which factor must be carefully accounted for that is less critical in single-story testing?

Answer: Stack effect influence on pressure readings

Stack effect is amplified in taller homes due to the greater vertical distance, which can significantly affect pressure readings and blower door results, especially in cold weather.

What is the correct procedure when wind speeds exceed acceptable limits during a blower door test?

Answer: Postpone or reschedule the test until wind conditions are acceptable

High winds create pressure fluctuations that compromise test accuracy; RESNET and ASTM standards recommend postponing testing when wind conditions exceed acceptable thresholds.

A rater notices that the blower door reading fluctuates significantly during testing even at steady fan speed. The most likely cause is:

Answer: High wind conditions causing pressure fluctuations

Significant fluctuations in pressure readings during a steady blower door test are most commonly caused by gusty or high wind conditions creating variable external pressure.