Measuring house air leakage with a blower door ~> Air leakage can increase heating and cooling costs over 30% and contribute to comfort, health and safety problems. Finding hidden air leakage sites, called bypasses, can be difficult without the use of a blower door. This diagnostic equipment uses a fan to pressurize (force air into) or depressurize (force air out of) a building. When the fan operates, it is easy to feel the effects of infiltration – air leaking through cracks in the building envelope. Blower doors have gauges which can measure the relative leakiness of a building. One measure of a home’s leakage rate is air changes per hour (ACH), which estimates how many times in one hour the entire volume of air inside the building leaks to the outside. Leakier houses have higher ACH’s, therefore higher heating and cooling costs, and greater potential for moisture, comfort, and health problems. To determine ACH50, the blower door creates a pressure difference of 50 Pascals between inside and outside. Fifty Pascals is approximately equivalent to a 20 m.p.h. wind blowing against all surfaces of a building. The leakier the house, the harder the fan must work to maintain the pressure. The amount of air the fan blows, measured in cubic feet per minute (CFM), is used to determine ACH.
Blower Door / Duct Blaster Test
Total Leakage ~> Duct leakage testing equipment is connected to the air handler to pressurize (or depressurize) the taped-over duct system to 25 Pascals. This is about the pressure that an HVAC system normally experiences. The blower door is not used for this test. The Total CFM25 amount of duct leakage is determined.
Leakage to outside ~> Since some duct leakage may occur within the conditioned space and is not necessarily bad from an energy standpoint, an additional duct test is performed to measure Leakage To Outside. For this test, the blower door is used to pressurize the house to 25 Pascals and the duct leakage testing equipment pressurizes the ductwork to the same level. All duct leakage that is measured is lost to the outside, or unconditioned space, and represents heating or cooling energy that is directly wasted.