HERS Blower Door & Duct Testing 2 — Questions and Answers
Question 1: During a blower door test, what effect does a large open fireplace damper have on the result?
- It has no measurable effect
- It increases the measured CFM50, making the house appear leakier (Correct answer)
- It decreases the measured CFM50 by creating a backdraft
- It causes the fan to stall
Correct answer: It increases the measured CFM50, making the house appear leakier
An open fireplace damper is a large pathway to outside and will increase the measured infiltration (CFM50), inflating the apparent leakage of the building shell.
Question 2: What is the primary reason HERS raters must depressurize ducts to a specific pressure (typically 25 Pa) during a duct leakage test?
- To replicate worst-case wind conditions
- To standardize results so tests from different homes and raters are comparable (Correct answer)
- To maximize airflow through the ducts
- To satisfy fire code requirements
Correct answer: To standardize results so tests from different homes and raters are comparable
Standardizing at 25 Pa ensures that duct leakage measurements are consistent and comparable across different test conditions, homes, and raters.
Question 3: In a duct leakage test, CFM25 total is measured at 300 cfm and CFM25 out is measured at 180 cfm. What is the duct leakage to outside?
- 480 cfm
- 300 cfm
- 120 cfm (Correct answer)
- 180 cfm
Correct answer: 120 cfm
Duct leakage to outside equals total leakage minus leakage to conditioned space: 300 − 180 = 120 cfm.
Question 4: Which condition must be established before starting a blower door test according to RESNET standards?
- All interior doors must be open (Correct answer)
- The HVAC system must be running at full capacity
- Combustion appliances must be turned off and flues sealed
- Windows must be left partially open for pressure relief
Correct answer: All interior doors must be open
RESNET requires all interior doors to be open so that the entire conditioned envelope is pressurized or depressurized uniformly during testing.
Question 5: What does a high ELA (Effective Leakage Area) value indicate about a home?
- The home has excellent air sealing
- The home has a large equivalent hole size and poor air sealing (Correct answer)
- The HVAC system is oversized
- The windows are energy efficient
Correct answer: The home has a large equivalent hole size and poor air sealing
A high ELA means the combined leakage pathways are equivalent to a large hole, indicating poor envelope air tightness.
Question 6: During duct leakage testing, why is it important to seal all supply and return grilles before testing?
- To prevent dust from entering the duct system
- To isolate duct leakage from building envelope leakage (Correct answer)
- To increase duct pressure above 25 Pa
- To comply with OSHA confined space rules
Correct answer: To isolate duct leakage from building envelope leakage
Sealing grilles ensures that airflow measured by the duct blaster represents only leakage through duct seams and connections, not intentional supply/return openings.
Question 7: A home tests at 6 ACH50. Which HERS reference home air leakage rate would this most closely correspond to for a typical new construction standard?
- It exceeds the typical new construction benchmark of 3 ACH50 (Correct answer)
- It meets the ENERGY STAR requirement of 7 ACH50
- It is at the Passive House standard of 0.6 ACH50
- It equals the IECC 2021 mandatory maximum
Correct answer: It exceeds the typical new construction benchmark of 3 ACH50
A common new construction benchmark is 3 ACH50 or less; 6 ACH50 is twice that limit, indicating the home is leakier than typical code expectations.
HERS Blower Door & Duct Testing 2
During a blower door test, what effect does a large open fireplace damper have on the result?