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Figure 4. No mastic on return duct in plenum serving packaged heating and cooling unit. Mastic used elsewhere in the plenum and throughout house.

Figure 5. Above Misalignment of round duct to round cutout. Arrow shows where components should mate. Below Misalignment/insufficient connection surface at round duct collar to rectangular duct.

Challenges to Achieving Duct Tightness Recommendations

After BAIHP makes recommendations in a Trip Report, the factory staff work out solutions to the problems identified. Often, problems identified during a test can be quickly located in other duct systems on the production line. The problems most often encountered mirror those identified by BAIHP staff during field work with moisture and air flow damaged manufactured homes (Moyer, et al, 2001). The most commonly encountered challenges include:

• Leaky supply and return(Fig. 4) plenums
• Misalignment of components (Figure 5), for example, floor boots not reaching or not being lined up with trunk ducts (in-line floor ducts)
• Free-hand cutting of holes in duct board and sheet metal without templates, often with “home made” tools or utility knives (Fig. 6), for example, a hole for a crossover collar not being round creates a poor collar connection, holes in trunk duct for floor boots cut too large for floor riser, creating a hard-to-seal hole)
• Insufficient connection area at joints (Fig. 5, bottom), for example, supply plenum and drop-out collar that are same dimension as the trunk duct.
• Mastic applied to dirty (sawdust) surfaces
• Insufficient mastic coverage
• Mastic applied to some joints and not others
• Loose strapping on flex duct connections
• Incomplete tabbing of fittings (Fig. 7, bottom)
• Poor tape application

Figure 6. Left Holes cut free hand do not mate well with duct system components. Note round duct is jammed into an oval shaped cut out. Right Imprecise rectangular cutout for ceiling register creates poor joint.

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