Measured Duct Leakage and Resulting Envelope Pressure Differences

As concern about IAQ has increased, forced-air distribution systems are being viewed as a potentially important factor in preventing the transport of indoor and outdoor pollutants. Duct leakage can be a confounding factor in attempts to use the forced-air system for this purpose. Leakage from outside into the return side of the system brings outdoor air directly into the distribution system through the leak. Supply leakage depressurizes the house which increases infiltration of outdoor air through the envelope. This paper presents results from three projects on field measurements of duct leakage, covering 77 homes in three regions of the U.S.: the Pacific Northwest, Wisconsin, and Central Illinois. These homes range in age from new to over 100 years old. Changes in house pressures due to duct leakage are reported. Duct leakage results are also compared to predicted changes in infiltration based on blower door results and infiltration models.