HERS Diagnostic and Field Testing 2 — 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.
HERS Diagnostic and Field Testing 2
When performing a duct leakage test, which metric is used to express total duct leakage in RESNET standards?