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PVC duct fittings
Ducts in Attics and Crawlspaces
Breaches can result in significant air leakage, since both supply
and return ducts are under typical pressures of 40-80 pascals
(Pa). All of the concerns for attic duct systems apply to crawlspace
systems, except high temperatures that speed the breakdown of
duct tape may not be present.
" Metal ducts. Breaches can be located at the joints where
both round and square metal duct lengths connect to each other
and where they attach to fittings and plenums. However, little
leakage comes from the longitudinal shop-bent joints (snap-lock)
in round and square ducts and from the factory swivel joints in
metal elbows (see Figure 3).
" Flex ducts. Leaks in flex ducts are found at connections
of the flex to junction boxes and fittings, and to leaks in the
junction boxes or fittings themselves. Duct board junction boxes
put together with foil-backed duct tape come apart over time,
and thus are a potential source of leakage. The metal collars
that fit into these boxes leak between the collar and the duct
board cut-out (see Figure 4). Metal junction boxes and fittings
used with flex duct have fabrication joints that also leak.
Ducts in concrete slabs. If bare galvanized ducts are used, sealing
all joints with mastic is recommended. The procedures for completely
encasing metal ducting joints with concrete will probably result
in little leakage. When using reinforced fiberglass ducts, the
common metal connectors, butyl gaskets, and PVC tape wrap should
provide an adequate seal.
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PVC
duct fittings
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