HERS Duct Leakage Testing 3 — Questions and Answers
Question 1: When performing a rough-in duct leakage test before drywall, what component is typically not yet installed and must be accounted for?
- The supply plenum
- The air handler or furnace (Correct answer)
- The return grilles
- The outdoor condensing unit
Correct answer: The air handler or furnace
At rough-in stage, the air handler is often not installed, so the test port must be used to cap that opening and simulate the sealed system.
Question 2: Which RESNET standard governs the procedure for measuring duct leakage in residential buildings?
- RESNET/ICC 380 (Correct answer)
- RESNET/ACCA 310
- RESNET 55-2006
- ASHRAE 152
Correct answer: RESNET/ICC 380
RESNET/ICC 380 is the standard that specifies test methods for measuring building airtightness and duct leakage used by HERS raters.
Question 3: A duct system located entirely within the conditioned envelope (e.g., inside conditioned basement) would have what expected Qto value?
- Higher than average because interior spaces are pressurized
- Approximately zero, since all leakage stays within conditioned space (Correct answer)
- Equal to total duct leakage minus supply leakage
- Undefined — Qto cannot be measured for interior ducts
Correct answer: Approximately zero, since all leakage stays within conditioned space
When all ducts are inside the conditioned envelope, any leakage stays within conditioned space, so leakage to outside (Qto) is effectively zero.
Question 4: What is the primary purpose of normalizing duct leakage results to conditioned floor area?
- To convert CFM25 to ACH for blower door comparison
- To allow fair comparison of leakage across homes of different sizes (Correct answer)
- To account for altitude effects on fan performance
- To determine the number of registers that need sealing
Correct answer: To allow fair comparison of leakage across homes of different sizes
Normalizing to floor area (CFM25/100 sq ft) creates a size-independent metric so duct tightness can be compared consistently across houses of varying sizes.
Question 5: During a post-construction duct leakage test, the rater finds leakage at 12 CFM25/100 sq ft but the project requires 6 CFM25/100 sq ft. What is the BEST next step?
- Retest at a lower reference pressure to get a passing result
- Locate and seal leakage points then retest (Correct answer)
- Apply a 20% variance allowance per RESNET guidelines
- Report the result and note that it is within typical industry range
Correct answer: Locate and seal leakage points then retest
When results exceed the threshold, the rater must identify and seal leaky duct connections, then conduct a retest to verify compliance.
Question 6: Which tool is specifically designed for measuring duct system leakage and generates a calibrated airflow at a target pressure?
- Blower door with depressurization ring
- Duct Blaster fan with pressure gauge (Correct answer)
- Pitot tube manometer set
- Anemometer with flow hood
Correct answer: Duct Blaster fan with pressure gauge
The Duct Blaster is a calibrated fan specifically engineered to pressurize duct systems to 25 Pascals and measure resulting airflow as an indicator of leakage.
Question 7: Why is mastic sealant generally preferred over standard duct tape for sealing duct leaks?
- Mastic is cheaper and easier to apply in tight spaces
- Mastic remains flexible and durable, while duct tape adhesive degrades over time (Correct answer)
- Mastic can be applied to live pressurized duct systems safely
- Mastic provides greater R-value to the duct surface
Correct answer: Mastic remains flexible and durable, while duct tape adhesive degrades over time
Mastic sealant maintains a durable, flexible seal over years of thermal cycling, whereas standard duct tape adhesive dries out and fails, allowing leaks to reopen.
HERS Duct Leakage Testing 3
When performing a rough-in duct leakage test before drywall, what component is typically not yet installed and must be accounted for?