HERS Blower Door & Duct Testing 3 — Questions and Answers
Question 1: What is the purpose of the pressure pan test in duct diagnostics?
- To measure total duct leakage at 25 Pa
- To locate which registers have the greatest duct leakage to outside (Correct answer)
- To verify that the air handler is operating at design airflow
- To calibrate the duct blaster fan
Correct answer: To locate which registers have the greatest duct leakage to outside
A pressure pan placed over each register measures the pressure difference behind it, identifying registers associated with ducts that leak outside the conditioned space.
Question 2: During a blower door test, which measurement channel on the manometer typically reads building pressure with respect to outside?
- Channel A
- Channel B
- The differential channel (B-A or A-B) (Correct answer)
- The absolute pressure channel
Correct answer: The differential channel (B-A or A-B)
The differential channel measures the pressure difference between inside and outside (or across the blower door fan), which is the key value for calculating air leakage.
Question 3: A rater finds that CFM25 out (duct leakage to outside) exceeds the RESNET threshold for the home size. What is the most appropriate next step?
- Report the result and recommend duct sealing, then retest (Correct answer)
- Increase fan speed and retest immediately
- Seal the blower door and cancel the test
- Replace all ductwork before filing the HERS rating
Correct answer: Report the result and recommend duct sealing, then retest
When duct leakage exceeds thresholds, the rater reports the finding, recommends corrective duct sealing by the contractor, and then conducts a retest to verify compliance.
Question 4: What term describes duct leakage that exits into an unconditioned space such as an attic or crawlspace?
- Duct leakage to inside
- Duct leakage to outside (Correct answer)
- Envelope leakage
- Balancing bypass
Correct answer: Duct leakage to outside
Duct leakage that goes into unconditioned spaces (attic, crawlspace, garage) is called duct leakage to outside because it effectively leaves the conditioned envelope.
Question 5: Which instrument is used to simultaneously measure fan flow and building pressure difference during a blower door test?
- Duct blaster only
- Digital manometer connected to the blower door fan and building (Correct answer)
- Infrared camera
- CO2 meter
Correct answer: Digital manometer connected to the blower door fan and building
A digital manometer measures both the pressure difference across the building envelope and the flow through the blower door fan, allowing CFM50 to be calculated.
Question 6: For HERS rating purposes, what does 'verified duct leakage' mean when ducts are entirely inside conditioned space?
- Only leakage to outside matters and is measured separately
- Total duct leakage is zero by definition
- The rater may use a default duct leakage value without testing (Correct answer)
- Duct leakage to outside is assumed to equal total leakage
Correct answer: The rater may use a default duct leakage value without testing
When all ducts are confirmed to be within the conditioned envelope, RESNET allows raters to use a default duct leakage assumption rather than requiring a measured test.
Question 7: What is the typical baseline depressurization target for a blower door test per ASTM E779?
- 10 Pa
- 25 Pa
- 50 Pa (Correct answer)
- 75 Pa
Correct answer: 50 Pa
ASTM E779 and RESNET protocols specify 50 Pascals as the reference depressurization pressure, which is why results are expressed as CFM50.
HERS Blower Door & Duct Testing 3
What is the purpose of the pressure pan test in duct diagnostics?