Assessment, Testing and Diagnostic Measurement
What gets measured
The assessment domain covers the tools and procedures used to characterize a house: blower door testing, duct leakage testing, pressure diagnostics, combustion analysis, and thermal imaging. Know what each test measures and its units. A blower door measures air leakage in CFM at a reference pressure (usually 50 Pa) and is reported as CFM50 or converted to ACH50 or CFM50 per square foot of envelope. Duct testing (pressurization or Delta-Q) measures leakage to outside versus total leakage.
Blower door interpretation
Understand that the blower door creates a pressure difference and measures airflow needed to hold it. Depressurizing the house pulls outside air in through leaks; pressurizing pushes inside air out. Use a manometer to read pressure pan values at outlets and recessed lights to find connected leaks. Zone pressure diagnostics help locate the leakage path between conditioned and unconditioned space.
Traps
Candidates confuse CFM50 with natural infiltration; CFM50 is a test condition, not normal operation. Another trap: assuming a lower ACH50 is always better without considering ventilation and combustion safety. Also watch for mixing up duct leakage to outside (the number that matters for energy) with total duct leakage.
Combustion and thermal tools
Know that a combustion analyzer measures CO, CO2, O2, and temperature to compute efficiency and stack conditions. An infrared camera shows surface temperature differences, not air leakage directly; it needs a temperature difference and can be fooled by emissivity and reflections.
Rule of thumb
A common benchmark: a house at 3 ACH50 or below is considered tight; above about 7 ACH50 is leaky. For a 2,000 sq ft house with 8 ft ceilings, 1,000 CFM50 is roughly 3.75 ACH50 (1,000 × 60 ÷ 16,000).