Blower Door Testing
A blower-door is a very useful building diagnostic tool that is used to quantify air leakage and differences in pressure in homes, offices, and any other heated and cooled buildings.
The blower-door uses a digital pressure gauge that displays pressure and air leakage figures in terms of Pascals (Pa) of pressure and cubic feet of air per minute (CFM). These numbers can then be interpreted by the inspector as to the relative leakiness of the building.
The most commonly used way for building-performance professionals to judge the relative "tightness" or "leakiness" of a building, with respect to other similarly-sized buildings, is CFM@50 Pascals. This is the total volume of air in a home that is turned over in one hour with a pressure difference from inside to outside of 50 Pascals. This simulates roughly 20 MPH winds hitting the house from every angle, at the same time.
Tightly constructed new homes may have a CFM50 number of 0.25-0.5 per square foot, so for example a 2,000 SF house (including basement) could be 500-1,000 CFM@50.
You will also hear about Natural ACH (air-changes per hour) when talking about indoor air quality. Typically code-built new homes will rate around 0.50-0.75 ACHn. Older, poorly air-sealed homes, with no weather-stripping may have readings higher than 1.5 ACHn. ENERGY STAR and other high-performance homes will be less than 0.35 ACHn, and at that tightness level mechanical ventilation is required.
When a blower-door is used in conjunction with an infrared camera, much greater detail on air-infiltration and insulation performance, or the lack thereof, can be seen with the thermal images produced.
While the blower-door is running, a pressure-pan can also be used to test for duct leakage in specific supply and return registers throughout the building. This simple test can show how leaky each individual supply and return duct is, or how "connected" each duct is to the outdoors.