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Appendix A:   Examination of Single Factory's Progress

A review of progress at a single factory gives a sense of the process of improving duct systems. Data and observations here are from a factory visited in February, April, and July of 2000. Initially, the duct systems were at Qn_total=10%.

The factory managers set out to achieve the Qn_total ≤ 6% goal, in preparation for building homes under the EPA Energy Star Program for Manufactured Housing. The managers and staff reached the goal by the third visit.

February 2000

The initial visit revealed that the factory was already using mastic. Two randomly selected sections were tested. Floor 1, a floor system, measured a Qn_total=10% falling short of the tightness goal. Floor 2, an overhead system, measured a Qn_total=5% meeting the goal.

Several problems with floor system assembly were observed and brought to the managers' attention in a trip report. These included misalignment of the trunk duct with the floor risers/boots cutouts; free hand hole cutting; insufficient mastic application to seal the floor boots, crossover collars, and furnace plenum; and loose straps.

Researchers recommended:

• Circle cutting tools
• Strap tightening tools (for flex duct zip ties)
• Improve placement of trunk ducts under riser holes precut in the sub-floor,
• Templates for cutting holes in the trunk duct to improve dimensional matching with the risers
• Increasing the size of the bead of mastic applied to joints.

April 2000

The second visit was to evaluate progress in implementing the recommendations made and achieving the goal of duct tightness, Qn_total ≤ 6%.

No ceiling systems were tested based on the performance found during the first visit and observation that all recommendations for overhead systems in the Trip Report had been implemented.

Observation of the floor system assembly found that alignment had improved, however, other issues were still unresolved:

• Holes for cross over collars and floor risers were still being cut free hand, leading to a host of assembly difficulties. For example, trunk duct holes were being cut too large, making riser attachment difficult and sometimes impossible.
• Workers were confused about where to seal the furnace plenum
• Not all the duct joints were being sealed
• Some joints were not getting adequate mastic

These improvements and remaining challenges were reflected in test results. Researchers tested two randomly selected sections with floor systems. Floor 1 measured a Qn_total=7%, down from 10% but just shy of the 6% goal. Floor 2 proved even closer to the goal at Qn_total=6.3%.

Recommendations reemphasizing the need to address these observed issues were detailed in a Trip Report.

July 2000
The third visit to the factory found substantial improvement to the floor duct system which was reflected in the test results. Three randomly selected houses were tested:

House 1
Floor 1 CFM25_total=45 (AHU side)
Floor 2 CFM25_total=27 (non-AHU side)
Combined CFM25_total=72
Combined Qn_total=5.4%

House 2
Floor 1 CFM25_total= 43(AHU side)
Floor 2 CFM25_total= 30(non-AHU side)
Combined CFM25_total=73
Combined Qn_total=4%

House 3
Floor 1 CFM25_total= 46(AHU side)
Floor 2 CFM25_total= 16(non-AHU side)
Combined CFM25_total=62
Combined Qn_total=3.8%

All three houses met the Qn_total = 6% goal after the recommendations for assembly improvement were implemented. This factory’s experience echoes that of other factories that BAIHP has worked with.

Continue to Appendix B - Duct Leakage and House Pressure Concepts >>