Secondary Author(s)

Withers Jr., Charles; Gu, Lixing; McIlvaine, Janet; Sonne, Jeffrey; Fairey, Philip; Lombardi, Matthew

Report Number




Simulation; Buildings; HVAC; Air Flow; Cooling; Energy Efficiency


In order to determine the impact of air handler location upon heating and cooling energy use, the amount of air leakage which occurs in the air handler cabinet needs to be known. Also, the leakage which occurs at the connections between the air handler cabinet and the return and supply plenums needs to be known as well because these connection leaks would also be located in the attic or any other location.

In order to assess this leakage, testing was performed on a total of 69 air conditioning systems. Thirty systems were tested in the year 2001 under funding from the Florida Department of Community Affairs. Twenty-nine additional systems were tested in 2002 also under funding from the Florida Department of Community Affairs. Ten additional systems were tested in 2002 under funding from the Brookhaven National Laboratory.

In each case, air leakage (Q25) at the air handler and two adjacent connections was measured. Q25 is the amount of air leakage which occurs when the ductwork or air handler (or any enclosed space) is placed under 25 pascals of pressure with respect to its surrounding environment. Q25 can also be considered a measurement of hole size. In order to obtain actual air leakage as the system is actually operated, it is necessary to also measure the operating pressure differential between inside and outside the air handler and adjacent connections. In other words, it is necessary to know the hole size and the pressure differential operating across that hole. By knowing both Q25 and operational pressure differentials, actual air leakage into or out of the system can be calculated. Throughout this report, the airtightness testing which has been performed is "total" (that is, leakage to both indoors and to outdoors). The only exception is during testing of the entire duct system in 20 of the 69 homes, both Q25,out and Q25,total were measured.

Date Published



Reference Publication: Cummings, J., Withers, C., Gu, L., McIlvaine J., Fairey, P., and Lombardi, M. "Field Testing and Computer Modeling to Characterize the Energy Impacts of Air Handler Leakage," FSEC­CR­1357­02

Local Subjects

Buildings - Air Flow; Buildings - Cooling; Buildings - Energy Efficiency; Buildings - HVAC; Simulation


FSEC Energy Research Center® Collection



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