HERS Blower Door & Air Infiltration 3 — Questions and Answers
Question 1: The RESNET ANSI 380 standard requires blower door tests to be conducted with interior doors in what position?
- All interior doors closed
- All interior doors open (Correct answer)
- Bedroom doors closed, common area doors open
- Doors in their normal operating position
Correct answer: All interior doors open
ANSI/RESNET/ICC 380 requires all interior doors to be open during blower door testing to ensure the entire conditioned volume is tested as a single zone.
Question 2: A rater is testing a house with a connected garage. According to RESNET standards, how should the garage be treated during the blower door test?
- Include the garage in the conditioned volume and leave the door open
- Seal the door between the house and garage and exclude the garage (Correct answer)
- Pressurize the garage separately
- Leave the garage door to the exterior open
Correct answer: Seal the door between the house and garage and exclude the garage
The garage is not part of the conditioned space, so the door between the house and garage should be closed (or sealed if leaky) and the garage is excluded from the test.
Question 3: What does the 'n' factor (pressure exponent) indicate in the blower door fan pressure-flow relationship equation Q = C × ΔP^n?
- The number of test points taken during the multi-point test
- The building's air permeability relative to a reference home
- The characteristic of the leakage openings (0.5 = large orifices, 0.65–0.75 = typical) (Correct answer)
- The conversion factor between CFM and cubic meters per hour
Correct answer: The characteristic of the leakage openings (0.5 = large orifices, 0.65–0.75 = typical)
The pressure exponent 'n' characterizes leakage opening types: 0.5 indicates large orifice-type openings, while values of 0.65–0.75 are typical for residential construction with mixed opening sizes.
Question 4: For HERS rating purposes, what is the primary metric derived from the blower door test that is used in energy modeling software like REM/Rate?
- ACH50 (air changes per hour at 50 Pa) (Correct answer)
- ELA (effective leakage area in square inches)
- CFM25 (flow at 25 Pa differential)
- SLA (specific leakage area as a ratio)
Correct answer: ACH50 (air changes per hour at 50 Pa)
ACH50 is the primary blower door metric entered into energy modeling software for HERS ratings to calculate infiltration's impact on heating and cooling loads.
Question 5: Which HERS Index range is generally associated with a home that achieves less than 3 ACH50 on the blower door test (assuming average efficiency in other systems)?
- HERS 120–140
- HERS 85–100
- HERS 60–75 (Correct answer)
- HERS 40–55
Correct answer: HERS 60–75
A home with very low air leakage (under 3 ACH50) typically achieves a HERS Index in the 60–75 range depending on other efficiency measures, significantly below the reference home score of 100.
Question 6: When performing a blower door test, why must fireplaces be sealed or have their dampers closed?
- To prevent back-drafting of combustion gases during the test
- Because fireplaces are intentional openings that would skew the envelope leakage measurement (Correct answer)
- To protect the manometer from soot contamination
- To prevent the test pressure from damaging the firebox liner
Correct answer: Because fireplaces are intentional openings that would skew the envelope leakage measurement
Fireplaces with open dampers are intentional large openings to the exterior; sealing them ensures the test measures only unintentional air leakage through the building envelope.
Question 7: A quality control inspector finds a blower door result of 7.2 ACH50 on a newly constructed home intended to meet ENERGY STAR v3.2 requirements. What is the correct action?
- Accept the result since it is below 10 ACH50
- Reject — the home must be air sealed and retested to meet the ≤5 ACH50 or ≤0.30 CFM50/ft² threshold (Correct answer)
- Apply a 15% correction factor for cold weather conditions
- Average this result with the duct leakage result
Correct answer: Reject — the home must be air sealed and retested to meet the ≤5 ACH50 or ≤0.30 CFM50/ft² threshold
ENERGY STAR v3.2 for most climate zones requires ≤5 ACH50 (or the equivalent CFM50/ft² metric), so 7.2 ACH50 fails and the home must be air sealed and retested.
HERS Blower Door & Air Infiltration 3
The RESNET ANSI 380 standard requires blower door tests to be conducted with interior doors in what position?