Furnace Installation and Owners Manual
41
LDJ620_E01_R03_2006.03
Models LDJ620-9 and LDJ620-10
AIR DISTRIBUTION SYSTEM INSTALLATION AND SEALING
Flexible nonmetallic ducts should not have an air-permeable
core. Flexible ducts must be stretched to their full length and
cut to fit (not compressed) using the minimum length required
to make the connection. Flexible duct that is not fully stretched
has high air-flow resistance and tends to sag between
supports. Connections and joints must be mechanically
fastened using drawstraps and sealed using mastic. Bends in
flexible ducts should not exceed 90 degrees and should have a
radius greater than one duct diameter.
A
I R
H
A N D L E R
Because system pressures are highest at the air handler, holes,
cracks, and other openings at the air handler will cause more
air leakage than elsewhere in the system. Air handlers located
in the attic, garage, or crawlspace, or outside in single-
packaged heat pumps or gas-packs, warrant special attention.
Use mastic, cork rope or tape, or caulk to permanently seal
unused holes, seams, wire penetrations, and refrigerant and
condensate line penetrations in the air handler cabinet. Use
approved pressure-sensitive tapes to seal access panels.
Connections between the air handler
cabinet and the main supply and
return plenums or ducts should be
sealed with mastic or approved
pressure-sensitive tapes. It is
sometimes easier to remove service
panels and seal these areas from the
inside using mastic.
P
L E N U M S
Fiberglass duct board is often used
to build supply and return plenums.
Mastics or approved tapes may be
used to assemble butt joints on
fiberglass duct board components
such as plenum boxes. Although it is
not recommended, closets, spaces
under stairs, and other such areas of
the house are often used as return
plenums. Because these plenums are
located inside the house, the need to
FLEX DUCT SEALING TIPS
seal them is often overlooked. Unless they are well sealed,
these plenums will frequently allow unconditioned air to be
drawn into the system from the attic, crawl space, or outside.
Be sure to seal all such plenums completely—all seams, gaps,
and penetrations through the ceiling, floor, and walls. Seal the
air handler unit to the shelf of a closet return system.
D
U C T
B
O O T S
A N D
E
L B O W S
Seal all joints between ducts, duct boots, and/or elbows with
mastic or approved tapes. Seal any leaks in the boots or elbows
with mastic, approved tape, or elastomeric caulk. Extend duct
boots at the supply and return registers through the wall,
ceiling, or floor material and make sure duct boots are sealed to
the ceilings, walls, or floors. Sometimes boots may be most
easily sealed from the inside, after installation; however, the
sealing material must be installed so that it does not interfere
with installation or removal of the register.
