HERS Diagnostic and Field Testing — Questions and Answers

Question 1: When performing a duct leakage test, which metric is used to express total duct leakage in RESNET standards?

CFM25 total (Correct answer)
ACH50
CFM50 total
Pascal differential

Correct answer: CFM25 total

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

Question 2: 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?

2.9% (Correct answer)
3.5%
4.2%
5.1%

Correct 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.

Question 3: During blower door testing, what does a high inside-out pressure differential (house more negative than outside) indicate?

The house is well-sealed
The fan is depressurizing the house as expected (Correct answer)
Duct leakage is pulling air in
The manometer is reading incorrectly

Correct 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.

Question 4: What is the purpose of a 'duct blaster' test conducted with the air handler fan OFF?

To measure envelope leakage only
To isolate and measure duct system leakage independently from the air handler (Correct answer)
To test the HVAC system's airflow capacity
To identify window and door leaks

Correct 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.

Question 5: Which condition would most likely cause an artificially LOW blower door reading during envelope testing?

High wind speeds outside
A large interior partition wall
An open window on the leeward side (Correct answer)
Stack effect from temperature differences

Correct 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.

Question 6: In a HERS duct leakage test, 'leakage to outside' differs from 'total leakage' because:

Total leakage includes supply and return separately
Leakage to outside only counts ducts outside conditioned space (Correct answer)
Total leakage measures at a different pressure
Leakage to outside excludes filter bypass leakage

Correct 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.

Question 7: 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?

They count as outside leakage because attics are always outside
They do NOT count as outside leakage since the attic is within the conditioned envelope (Correct answer)
They must be tested separately with a secondary duct blaster
They are excluded from HERS calculations entirely

Correct 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.

Question 8: 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 9: 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 10: 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 11: 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 12: 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 13: 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 14: 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.

Question 15: What pressure standard does RESNET use for normalizing envelope air leakage in a blower door test?

25 Pascals
50 Pascals (Correct answer)
75 Pascals
100 Pascals

Correct 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).

Question 16: A home tests at 1,850 CFM50 and has a volume of 12,000 cubic feet. What is the ACH50 value?

6.5 ACH50
9.25 ACH50 (Correct answer)
0.15 ACH50
15.4 ACH50

Correct answer: 9.25 ACH50

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

Question 17: In HERS field testing, what does 'verified' mean in the context of duct leakage testing?

The rater visually inspected all duct connections
A third-party certified rater performed and documented the measured test result on-site (Correct answer)
The builder provided documentation of duct installation
The HVAC contractor certified the duct system in writing

Correct 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.

Question 18: When a HERS rater tests a multi-story home, which factor must be carefully accounted for that is less critical in single-story testing?

Total floor area calculation
Stack effect influence on pressure readings (Correct answer)
Number of HVAC systems installed
Window U-factor verification

Correct 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.

Question 19: What is the correct procedure when wind speeds exceed acceptable limits during a blower door test?

Proceed with the test and note wind conditions in the report
Postpone or reschedule the test until wind conditions are acceptable (Correct answer)
Seal all windows on the windward side and retest
Increase the blower door pressure to 75 Pascals to overcome wind effect

Correct 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.

Question 20: A rater notices that the blower door reading fluctuates significantly during testing even at steady fan speed. The most likely cause is:

Faulty manometer calibration
A large operable skylight left partially open
High wind conditions causing pressure fluctuations (Correct answer)
The HVAC system is cycling on and off

Correct 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.

Question 21: For HERS rating purposes, when must duct leakage testing be performed during construction?

Only after drywall is installed and finished
Before insulation is installed to allow visual inspection
Before ducts are covered, sealed, or made inaccessible — rough-in stage or final (Correct answer)
At final occupancy after all systems are commissioned

Correct answer: Before ducts are covered, sealed, or made inaccessible — rough-in stage or final

Duct leakage testing must occur either at rough-in (before ducts are covered) or at final completion; RESNET allows either stage but the ducts must be accessible or testable.

HERS Diagnostic and Field Testing

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

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