Blower Door test

The blower door test measures the amount of air that flows into or out of a house while maintaining a set pressure difference between the indoors and outside. By using a calibrated fan and metering equipment, airflow can be measured at a variety of pressure differences. The blower door test is used to determine the airtightness of a home. A leaky house will lose conditioned air (and hence, energy) to the outdoors or draw unconditioned air indoors. A very airtight house without ventilation can develop indoor air quality issues under some circumstances. A blower door test can also indicate construction quality as well as compliance with design or program standards.

http://www.eere.energy.gov/consumer/your_home/energy_audits/index.cfm/mytopic=11190

http://www.energyconservatory.com/applications/applications3.htm