Diagnostics & Performance Testing Flashcards

A HERS rater tests a new home with a target of 3 ACH50 and measures 2.8 ACH50. The rater should:

Answer: Record a passing result and document the measured value

A measured 2.8 ACH50 is below the 3.0 ACH50 target, so the home passes and the rater records the actual measured value.

Which of the following conditions would cause a blower door test to produce an artificially low (better) result?

Answer: Testing in high wind conditions

High exterior wind creates positive or negative pressure on the building that interferes with the blower door reading, often producing artificially lower leakage values on the windward side.

For HERS rating purposes, what does the term 'infiltration volume' refer to in the building envelope leakage calculation?

Answer: The conditioned floor area multiplied by ceiling height used to normalize CFM50 into ACH50

ACH50 is calculated by dividing CFM50 × 60 by the conditioned volume (floor area × ceiling height), so this volume is essential for normalizing the leakage metric.

A rater measures HVAC system total external static pressure (TESP) at 0.85 in. w.c. on a system designed for 0.50 in. w.c. What is the likely consequence?

Answer: Reduced airflow, potential coil icing, and compressor stress

Excessive static pressure restricts airflow below design levels, which can cause evaporator coil freezing and premature compressor failure due to poor heat exchange.

Under ANSI/RESNET/ICC 380, what is the minimum number of blower door tests required to use sampling for a production builder with 12 certified homes in a rating period?

Answer: At least 1 test plus additional tests per sampling protocol requirements

RESNET sampling protocols require a minimum initial sample and additional tests if failures occur; the exact number depends on the rating period rules, but at least one test plus protocol-driven additional tests are required.

A rater uses the subtraction method for duct leakage testing. She measures a total duct leakage of 180 CFM25 and a house-to-outside leakage contribution of 50 CFM25 with registers sealed. What is the calculated duct leakage to outside?

Answer: 130 CFM25

Leakage to outside = total duct leakage minus the house contribution: 180 − 50 = 130 CFM25.

When conducting a HERS inspection, why must the rater verify the HVAC equipment capacity against the Manual J load calculation?

Answer: To confirm the system is not grossly oversized or undersized, which affects efficiency and comfort ratings

Properly sized equipment runs longer cycles, maintains better humidity control, and achieves rated efficiency; gross oversizing or undersizing can fail HERS compliance and comfort thresholds.