Documentation Conflict: Two Technicians, Two Numbers
A quality-control reviewer is auditing a file for a 2,600 square foot house. The file contains two blower door reports. Report A, dated March, lists CFM50 = 2,400, ACH50 = 3.1, and notes "front door, single fan, calm." Report B, dated June, lists CFM50 = 3,050, ACH50 = 3.9, and notes "garage door setup, two fans, windy." Neither report states the conditioned volume used, the gauge calibration date, the baseline pressure, or whether interior doors were opened. The program threshold is 3.0 ACH50. The builder submitted Report A to the program and kept Report B in the project file. The reviewer asks you to determine which number is defensible.
1. Identify the documentation gaps and explain how each one undermines defensibility.
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Gaps and their consequences:
Conditioned volume not stated. ACH50 is CFM50 × 60 divided by volume. Report A implies a volume of (2,400 × 60) / 3.1 = 46,452 ft³, which for 2,600 ft² is about 17.9 ft average height - implausible for most houses. Report B implies (3,050 × 60) / 3.9 = 46,923 ft³, essentially the same volume. The numbers are internally consistent with each other but the volume is unstated and cannot be verified, so neither ACH50 can be independently checked.
Calibration date missing. Without it, the reviewer cannot establish that the gauge was within its calibration interval. An out-of-calibration gauge invalidates the measurement regardless of technique.
Baseline pressure missing. No zero-flow baseline is recorded, so there is no evidence the readings were corrected for stack and wind effects. Report B's "windy" note makes this a live concern.
Interior door state unstated. Interior door position changes the pressure field and therefore the measured leakage. It must be documented.
Setup inconsistency. Report A used a single fan at the front door; Report B used two fans at the garage door. Different setups, different seasons, different wind conditions - the two numbers are not directly comparable and the discrepancy is at least partly methodological.
Each gap alone is enough to make a report questionable; together they make both reports weak.
2. The builder argues Report A is the valid one because it passes the 3.0 threshold. How do you rule, and what should the reviewer require?
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Ruling: neither report is currently defensible, and the pass/fail argument is not the deciding factor.
Why the builder's reasoning fails: Selecting the report that passes is not a technical justification. Report A passes at 3.1 ACH50 only if its unstated volume is correct; the implied volume is implausible, so the 3.1 may be wrong in either direction. A number that cannot be reconstructed from the file cannot be certified, whether it passes or fails.
Why Report B is not automatically better: It is more conservative and its notes are more candid about conditions, but "windy" with no baseline recorded means its 3,050 CFM50 may include wind-induced error. Two fans at a garage door is a valid setup but must be documented with the fan configuration and the door preparation.
What the reviewer should require:
- A single new test run under documented conditions: measured conditioned volume, stated setup and fan configuration, interior doors as specified, zero-flow baseline recorded, wind noted, gauge calibration date on the report.
- Correction of the ACH50 using the verified volume.
- A written explanation in the file of why the March and June tests differ, referencing setup and weather.
- Retention of both prior reports with the new one - do not delete the inconvenient result.
Bottom line: The file is resolved by a properly documented re-test, not by choosing the favorable number.
3. Draft the short technical note you would place in the file explaining the discrepancy to a future reviewer.
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Technical Note - Blower Door Discrepancy, Project File
Two blower door tests are on file for this 2,600 ft² residence:
- Test A (March): 2,400 CFM50, 3.1 ACH50, single fan, front door, calm conditions.
- Test B (June): 3,050 CFM50, 3.9 ACH50, two fans, garage door, windy conditions.
Assessment: The 650 CFM50 difference (about 27 percent) is not attributable to a single cause on the available records. Contributing factors likely include different fan configurations and test locations, different wind conditions (Test B was run in wind with no recorded baseline), and possible differences in interior door state, none of which were documented. Neither report records conditioned volume, gauge calibration date, or baseline pressure, so neither ACH50 can be independently verified. The implied volume in both reports (approximately 46,500 ft³) is inconsistent with the stated floor area and requires confirmation.
Disposition: Neither report is accepted as the compliance value. A new test will be performed with documented conditioned volume, fan configuration, test location, interior door state, zero-flow baseline, wind conditions, and gauge calibration date. Both prior reports are retained in the file. The new result supersedes both for compliance purposes.
Prepared by: ________________ Date: ____________
This note is written so a reviewer who never speaks to either technician can see what was done, what was wrong, and why the replacement test is the one to trust.