Evaluation of two new duct leakage measurement methods in 51 homes

Duct leakage in forced-air distribution systems has been recognized for years as a major source of energy losses in residential buildings. Unfortunately, the distribution of leakage across homes is far from uniform, and measuring duct leakage under normal operating conditions has proven to be difficult.
Recently, two new methods for estimating duct leakage at normal operating conditions have been devised. These are called the nulling test and the delta-Q test. This paper presents the results of a study on 51 homes to evaluate these new methods relative to an independent benchmark and a method that is currently used. The nulling test was found to perform well as long as wind effects
were minimal. Unfortunately, the time and difficulty of setup can be prohibitive, and it is likely that this method will not be practical for general use by contractors except in homes with no return
ducts. The delta-Q test was found to have a bias, resulting in overprediction of the leakage, which qualitatively confirms the results of previous laboratory, simulation, and small-scale field studies.
On average, the bias was only a few percent of the air-handler flow, but in about 20% of the homes the bias was large. A primary flaw with the delta-Q test is the assumption that the pressure between the ducts and the house remains constant during the test, as this assumption does not hold true.