Primary Author(s)

Florida Solar Energy Center

Secondary Author(s)

Cummings, James; Moyer, Neil

Report Number




Air Flow; Buildings; Ducts; Florida; Energy Consumption; Blower Door; HVAC


Testing for air leakage in air distribution systems was done in 160 central Florida homes. Tracer gas tests found that infiltration rates were three times greater when the air handler was operating that when it was off, indicating that there are large leaks in the air distribution system. Infiltration averaged 0.91 air changes per hour (ach) with the air handler (AH) operating continuously and 0.28 ach with the AH off. Return leaks were measured by tracer gas and found to average 10.7% of AH total flow. House airtightness, in 99 of these homes, determined by blower door testing, averaged 12.7 air changes per hour at 50 Pascals (ACH50). When the duct registers were sealed, ACH50 decreased to 11.1, indication that 12.7% of the house leaks were in the air distribution system.

Duct leaks were repaired in 50 of the 160 homes. Blower door tests were done on these houses before and after repair. Before repair airtightness was 12.5 ACH50. After repair house ACH50 decreased to 11.2, indicating that 63.7% of the duct leaks were repaired. Infiltration tests were done before and after repair on 25 of these homes. Infiltration rates with the AH on decreased from 16.0% to 4.5% of total air handler flow.

Cooling energy use decreased as a result of duct repairs. Data was available for 46 of the 50 homes. Air conditioner energy use decreased by an average 17.2%, yielding estimated space conditioning energy savings of $110 per year. Duct repairs are a very cost-effective retrofit. At an average cost of $200 per home, duct repairs have a simple payback of less than two years.

Duct leaks have a dramatic impact upon peak electrical demand. While no peak demand data has yet been measured, theoretical analysis indicates that a 15% return leak from the attic can increase cooling electrical demand by about 90%. Detailed theoretical analysis of a winter Florida morning indicates that duct repairs in a typical, electrically heated Florida home reduce winter peak demand by about 1.6 kW per house at about one-sixth the cost of building new electrical generation capacity. Repair of ducts in 3 million Florida homes could reduce winter peak demand by 5000 megawatts, of 13% of the state's generating capacity. This effort would be very cost effective, since the generation capacity made available by duct repair would cost only abut one-third to one-eighth what new capacity would cost, depending upon type of generation facility.

Date Published



Reference Publication: Cummings, J.B., Tooley, J. Jr., Moyer N., "Investigation of Air Distribution System Leakage and Its Impacts in Central Florida Homes", Prepared for the Governor's Energy Office, FSEC­CR­397­91, January 31, 1991.

Local Subjects

Buildings - Air Flow; Buildings - Blower Door; Buildings - Ducts; Buildings - Energy Consumption; Florida; Buildings - HVAC


FSEC Energy Research Center® Collection



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