Audit Data Collection and Diagnostic Testing
What to Collect
A complete audit gathers: building dimensions and geometry, insulation levels and types, window and door specs, HVAC equipment nameplate data, duct layout, and occupant comfort complaints. Record baseline conditions (thermostat setpoints, weather) so results are interpretable. Document with photos and a consistent data sheet; missing data is the most common source of failed audit reports.
Blower Door Testing
Know the CFM50 metric and the ACH50 calculation: ACH50 = CFM50 × 60 / conditioned volume. A 2,000 ft² home with 8-ft ceilings has 16,000 ft³; at 2,400 CFM50, ACH50 = 2,400 × 60 / 16,000 = 9.0. Understand CFM50 per ft² of envelope and the difference between CFM50 and natural infiltration (roughly CFM50/15 to /20, climate dependent). Traps: using floor area instead of volume, forgetting to correct for altitude or temperature, and confusing ACH50 with ACHn.
Duct and Zone Testing
Duct leakage is measured with a duct blaster; report leakage as CFM25 and as a percentage of system airflow. Pressure pan readings identify which ducts leak to outdoors vs. conditioned space. Zone pressure diagnostics reveal connected cavities.
Other Diagnostics
Infrared imaging shows temperature differences, not air leakage directly-require a Delta-T. Combustion analyzer gives CO, CO2, and efficiency. Gas leak detection and CAZ depressurization testing are mandatory before and after air sealing.
Rule of thumb: If ACH50 is above ~10 in a cold climate, prioritize air sealing; below ~3, focus on insulation and mechanicals.