HERS Diagnostics & Performance Testing 3 — Questions and Answers
Question 1: During a combustion appliance zone (CAZ) test, the technician finds that a draft hood-equipped water heater depressurizes the CAZ by 5 Pa when all exhaust fans run simultaneously. What does this indicate?
- The appliance is in good working condition
- There is a spillage risk and corrective action may be needed (Correct answer)
- The water heater is oversized for the space
- The test passed because 5 Pa is the maximum allowable limit
Correct answer: There is a spillage risk and corrective action may be needed
Depressurizing a CAZ by 5 Pa or more while draft-hood appliances are present can cause backdrafting or spillage, requiring further investigation and remediation.
Question 2: Which RESNET standard governs HERS field verification sampling protocols?
- RESNET Publication 002
- ANSI/RESNET/ICC 380 (Correct answer)
- ASHRAE 62.2
- IECC Section R405
Correct answer: ANSI/RESNET/ICC 380
ANSI/RESNET/ICC 380 establishes the test methods and field verification protocols used by HERS raters for sampling and diagnostic testing.
Question 3: A HERS rater is verifying insulation in a vented attic. The rated R-value is R-38 but the depth gauge shows an average of 9.5 inches of blown fiberglass. What is the likely finding?
- Pass, because blown fiberglass always exceeds labeled R-values
- Fail, because 9.5 inches of blown fiberglass typically provides approximately R-30, not R-38 (Correct answer)
- Pass, if the contractor's certificate states R-38
- Fail only if settled depth is less than 8 inches
Correct answer: Fail, because 9.5 inches of blown fiberglass typically provides approximately R-30, not R-38
Blown fiberglass provides roughly R-2.5 to R-3 per inch; at 9.5 inches that is approximately R-24 to R-29, well short of R-38.
Question 4: What is the primary reason a HERS rater depressurizes the house to -50 Pa during a blower door test rather than a lesser pressure?
- To detect moisture intrusion in the walls
- To amplify small leaks so they can be measured accurately and reproducibly (Correct answer)
- To simulate hurricane wind conditions
- To test the structural integrity of windows and doors
Correct answer: To amplify small leaks so they can be measured accurately and reproducibly
Testing at -50 Pa creates a standardized pressure that amplifies airflow through small cracks, making them measurable and results comparable across different homes and testers.
Question 5: When using a duct blaster to measure duct leakage to outside (Qout), the technician must cancel out house leakage. Which technique accomplishes this?
- Sealing all registers and pressurizing only the duct system
- Simultaneously operating the blower door to maintain house pressure equal to duct pressure (Correct answer)
- Running the air handler at full speed during the test
- Testing only in cold weather to avoid thermal convection errors
Correct answer: Simultaneously operating the blower door to maintain house pressure equal to duct pressure
The simultaneous blower door and duct blaster technique pressurizes the house to equal the duct test pressure, canceling house leakage so only duct-to-outside leakage is measured.
Question 6: A rater measures window U-factor using a NFRC label that reads 0.30. The energy model uses 0.28. Which value should be used for compliance verification?
- The modeled value of 0.28 always takes precedence
- The NFRC-labeled value of 0.30 as the as-built condition (Correct answer)
- The average of 0.29 for conservatism
- Either value, because the difference is within rounding tolerance
Correct answer: The NFRC-labeled value of 0.30 as the as-built condition
Field verification must reflect as-built conditions; the NFRC label on the installed product (0.30) is the verified value and must be entered into the energy model.
Question 7: What does a high 'worst-case' CAZ depressurization reading indicate during a combustion safety test?
- The HVAC system is well-balanced
- Exhaust fans and the HVAC system together create enough negative pressure to cause appliance backdrafting (Correct answer)
- The house is too tight for Energy Star certification
- The combustion appliances are over-firing
Correct answer: Exhaust fans and the HVAC system together create enough negative pressure to cause appliance backdrafting
High worst-case CAZ depressurization means the combined operation of exhaust devices creates sufficient negative pressure to overcome natural draft and pull flue gases back into the living space.
HERS Diagnostics & Performance Testing 3
During a combustion appliance zone (CAZ) test, the technician finds that a draft hood-equipped water heater depressurizes the CAZ by 5 Pa when all exhaust fans run simultaneously.
What does this indicate?