HERS Duct Leakage Testing 2 — Questions and Answers
Question 1: What does the term 'duct leakage to outside' (Qto) specifically measure?
- Total air leaking from all duct seams
- Air leaking between the duct system and unconditioned space (Correct answer)
- Air leaking from supply registers only
- Pressure difference across the air handler
Correct answer: Air leaking between the duct system and unconditioned space
Duct leakage to outside (Qto) measures air exchanged between the duct system and unconditioned spaces such as attics, crawlspaces, or garages.
Question 2: During a duct leakage test, all registers are sealed with tape and plugs. What is the purpose of this step?
- To prevent backdrafting from combustion appliances
- To isolate the duct system so only duct envelope leakage is measured (Correct answer)
- To increase static pressure for accurate fan readings
- To test each branch independently
Correct answer: To isolate the duct system so only duct envelope leakage is measured
Sealing registers isolates the duct system from the living space so that the Duct Blaster measures only leakage through duct seams and connections.
Question 3: A home has a Duct Leakage to Outside of 8% of floor area. Under ENERGY STAR v3.2, what is the maximum allowable Qto as a percentage of conditioned floor area?
- 4% (Correct answer)
- 6%
- 8%
- 10%
Correct answer: 4%
ENERGY STAR v3.2 requires duct leakage to outside to be no more than 4 CFM25 per 100 sq ft of conditioned floor area.
Question 4: What unit is most commonly used to express duct leakage test results in the U.S.?
- Pascals per hour (Pa/hr)
- CFM at 25 Pascals (CFM25) (Correct answer)
- Air Changes per Hour (ACH)
- Liters per second (L/s)
Correct answer: CFM at 25 Pascals (CFM25)
Duct leakage in the U.S. is standardized at CFM25, meaning cubic feet per minute of airflow at 25 Pascals of induced pressure.
Question 5: Which of the following conditions would MOST likely cause a duct leakage test to underestimate actual leakage?
- Wind causing exterior pressure fluctuations
- Registers that were not fully sealed before testing (Correct answer)
- A Duct Blaster fan set to too high a flow rate
- An air handler blower left running during the test
Correct answer: Registers that were not fully sealed before testing
Incompletely sealed registers allow conditioned air to pass through, bypassing the Duct Blaster and causing the measured leakage to be lower than actual.
Question 6: How does the 'pressure matching' technique help when testing duct leakage to outside?
- It equalizes pressure between supply and return ducts
- It pressurizes the house to match duct pressure, isolating outside leakage (Correct answer)
- It calibrates the Duct Blaster fan to ambient conditions
- It removes the need to seal registers during testing
Correct answer: It pressurizes the house to match duct pressure, isolating outside leakage
Pressure matching uses a blower door to bring the house to the same pressure as the duct system, effectively nullifying leakage paths through the building envelope and isolating outside leakage.
Question 7: A Duct Blaster reading shows 180 CFM25 total leakage for a 1,800 sq ft home. What is the duct leakage expressed as CFM25 per 100 sq ft?
- 5 CFM25/100 sq ft
- 10 CFM25/100 sq ft (Correct answer)
- 18 CFM25/100 sq ft
- 100 CFM25/100 sq ft
Correct answer: 10 CFM25/100 sq ft
180 CFM25 ÷ 1,800 sq ft × 100 = 10 CFM25 per 100 sq ft of conditioned floor area.
HERS Duct Leakage Testing 2
What does the term 'duct leakage to outside' (Qto) specifically measure?