Energy Assessment and Diagnostic Testing: Measuring Instead of Guessing
Energy Assessment and Diagnostic Testing covers how you measure a house: blower door, duct blaster, manometer, infrared camera, combustion analyzer, and the bill analysis that frames the visit. Exam items test whether you choose the right test, run it under valid conditions, and convert raw readings into the metrics programs actually use.
Start with the bill, not the tools
Split base load from seasonal load. Compare a mild month with a cold month: the difference is weather-dependent use driven by space conditioning and duct loss; the flat portion is base load (water heating, appliances, well pump). Base load above roughly 400–500 kWh/month in a typical gas-heated home is a flag for a failing water heater, an old refrigerator, or a pump running continuously.
Blower door metrics
CFM50 is raw leakage at 50 Pa. Convert it: ACH50 = CFM50 × 60 ÷ conditioned volume. Normalize by envelope area (CFM50/ft²) when comparing homes of different size. Zonal pressure diagnostics - pressure pans, interior door closures - locate the leak path, not just its size. Expect roughly ±10% repeatability; do not hang a claim on a 5% difference.
Duct leakage
A duct blaster measures total leakage. A second test with the house pressurized (or with the air handler off and registers masked correctly) separates leakage to outside from leakage to conditioned space. Program thresholds are usually written as CFM25 per 100 ft² of conditioned floor area.
Valid test conditions
Blower door results degrade with wind and with small indoor-outdoor temperature differences; common practice avoids sustained wind above about 15 mph and ΔT below about 15°F. Infrared scans need a similar ΔT (often 10–15°F) plus low solar gain, so scan early morning or on a cloudy day, and treat hot spots as qualitative unless emissivity and reflectivity are controlled.
Worked example. A 2,000 ft² home with 8 ft ceilings has a volume of 16,000 ft³. The blower door reads 3,000 CFM50. ACH50 = (3,000 × 60) ÷ 16,000 = 11.25. For context, 8–15 ACH50 is typical pre-weatherization, 2–3 ACH50 is a tight new home, and many programs target a 25% or greater reduction from baseline rather than an absolute number.
Traps that cost marks
- Running the blower door with the door to an attached garage or unconditioned basement open.
- Measuring duct leakage with the air handler running or registers taped incorrectly.
- Reading a pressure pan number as if it were an airflow measurement.
- Calling an infrared cold spot a leak without confirming it with a smoke pencil or zonal test.