Publication Index:

Conclusions Select Acknowledgements Executive Summary Building America Partnership Factory Visits, Data Collection, and Data Description Observations Challenges to Achieving Duct Tightness Recommendations Achieving Duct Tightness Recommendations Duct Tightness Data Economics of Duct Tightening in Manufactured Housing (see Appendix C) References Data Sources Appendix A - Examination of Single Factory's Progress Appendix B - Duct Leakage and House Pressure Concepts Appendix C - Letters from Manufacturers Regarding Cost

Reduced duct leakage has been proven to reduce homeowner utility bills while improving comfort, durability, and indoor air quality (Compilation of findings in Cummings, et al, '91 and '93, Davis '91, Evans, et al, '96, and Manclark, et al '96.) Duct leakage prevalence has been documented among site built homes (Cummings, et al, 1991, 1993, 2003), new manufactured homes (Tyson, et al, 1996. MHRA, 2003), and manufactured homes in failure due to moisture and air flow control issues (Moyer, et al, 2001).

BAIHP researchers measured total duct leakage (CFM25_total, Qn_total) and duct leakage to the outside (CFM25_out, Qn_out) in 190 new manufactured homes or sections between 1996 and 2003. The data set is described in Table 10. Taped  (58) and mastic sealed (132) duct systems are included.

Factories implementing duct tightening recommendations showed steady progress and were able to consistently produce duct systems that met the target tightness of Qn_total<=6%.

80 floors with mastic sealed duct systems were tested for both total and outside leakage. 58 achieved both Qn_total ≤ 6% and Qn_out ≤ 3%. Only one system achieved Qn_total ≤ 6% but not Qn_Out<=3%. This exception had a Qn_out=4.1%. An additional 14 mastic sealed systems met the Qn_out ≤ 3% with a Qn_total >6%, exceeding the total leakage goal.

BAIHP researchers will continue to use the Qn_Total<=6% target with manufacturers. The average ratio of outside leakage to total leakage in the mastic sealed systems was slightly lower than expected at 36%. This helps explain how some manufacturers not meeting the Qn_total ≤ 6% goal still met the Qn_out ≤ 3% goal.

Though measuring duct leakage to the outside is the only positive way to verify that the Qn_Out goal has been met, BAIHP feels confident recommending the approach documented here for assisting home manufacturers with meeting the Qn_Out<=3% goal. Of the 24 factories discussed in this paper, 22 were able to achieve the Qn_total ≤ 6% and/or the Qn_out ≤ 3% goals they set.

Summary of BAIHP Approach to Achieving Tight Ducts in Manufactured Housing:

• Set goal with factory management of achieving Qn_Out<=3% using Qn_Total<=6% as a surrogate measurement while houses are in production.
• Evaluate current practice by testing a random sample of units
• Report Qn_Total and Qn_Out findings; make recommendations for reaching goals
• Assist with implementation and problem solving as needed
• Evaluate results and make further recommendations until goal is met
• Assist with development of quality control procedures to ensure continued success

Finally, duct tightness goals can be achieved with minimal added cost. Reported costs range rom $4 to $8, including in-plant quality control procedures (testing) critical to meeting duct tightness goals.

Achieving duct tightness goals provides benefits to multiple stakeholders. Improving duct tightness diminishes uncontrolled air (and moisture) flow, including infiltration of outside air, loss of conditioned air from supply ducts, and introduction of outside air into the mechanical system. Uncontrolled air flow is an invisible and damaging force that can affect the durability of houses, efficiency and life of mechanical equipment, and sometimes occupant health. With improved duct tightness, manufacturers enjoy reduced service claims and higher customer satisfaction, while homeowners pay lower utility bills, breathe cleaner air, and have reduced home maintenance.

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