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HVACR115 – Mechanical for
Gas Heat
Sheet Metal Installation
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• http://www.youtube.com/watch?v=LJbFUM0Lnnw
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Sheet Metal Tools
• Sheet Metal Hammer
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• Tin Snips
– Right Hand: Red Handle-cuts left
– Left Hand: Green Handle-cuts right
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• Crimpers: Turns the end of metal pipe or fittings into a
crimped male end for connecting.
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• http://www.youtube.com/watch?v=uH5wRVVmgh8
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• Notchers: Used to notch corners of rectangular
ductwork before bending.
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• Folding Bar: Makes 1” bends for flanges or ½” “ears”
for connecting ducts with drive cleats
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• Hand Seamers: Makes ¼” to 1” bends
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• Bulldog Snips: Makes straight cuts of large sections of
sheet metal
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• Duct Stretchers: Brings the “ears” of two ducts closer
together in order to connect drive cleat.
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• Scratch Awl: Makes well defined lines in sheet metal
when laying out fittings.
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• Adjustable Dividers (Scribers, Compass): Used to
scribe radius angles on sheet metal.
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• Common method of connecting rectangular sheet metal
ducts:
– Using drive cleats and S-slip.
– S-slip or S-locks slide over horizontal edges of one piece of
rectangular duct.
– Vertical edges are folded back ½” to form “ears.
– Horizontal edges of second piece of duct are slipped into slock
– Drive cleats are hammered onto the two sets of ears.
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Drive Cleat
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• http://www.youtube.com/watch?v=WF8JZ1t_nm4
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• Hole Cutter: Make precise hole in sheet metal
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• http://www.thisoldhouse.com/toh/video/0,,20504377,00
.html
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• Flex duct cutter: Has knife for slicing flex membrane
and insulation, and pliers for cutting spiraled wire.
Comes with sheath.
• Hint: Never cut wire with tin snips.
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• Flex strap tightener
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• Turbo shears: Can be electric or air powered for fast
cuts
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• Stapler: Used to wrap insulation around duct.
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• Small tape measure for measuring radius,
circumference.
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Sheet Metal Fabrication Machinery
• Pittsburg (Lockformer) Machine:
• One side of a piece of sheet metal is run through
machine and formed to receive a ¼” edge on opposite
side.
• Flat sheet is bent into rectangle shape,
• Pittsburg is opened slightly with screwdriver,
• ¼” edge is inserted,
• Pittsburg is hammered over, locking into place.
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• http://www.youtube.com/watch?v=n8GLOFkOxjM&fe
ature=related
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• http://www.youtube.com/watch?v=-p4P4qoXMzQ
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• http://www.ronhazelton.com/projects/replacing_a_centr
al_air_conditioning_system
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Break: Used to bend sheet metal.
Can be 8’ for shop,
Or 4’ to transport to job for furnace replacements.
Counter weighted for ease of operation.
Never place hand between upper leaf and
bending leaf.
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• Shear: Used to slice sheet metal.
– Can be pneumatic with foot pedal,
– Or operated with foot lever.
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• Roller: Puts curves in
heels and thrats of
fittings.
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• Easy Edger: Puts ¼”
bead on cheeks of
fittings.
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Trunk Fittings
• Plenum: Also called bonnet.
• Is a sheet metal box attached to furnace or
air handler on either SA or RA side.
• Sides are cut into, and takeoffs attached.
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Takeoffs
• Usually have a ½” hem or flange.
• May have a clinch type collar
• Side that attaches to the plenum will have
½” hem or flange.
• This sides dimension should be larger than
the duct size to allow air to flow smoother.
• Should have a 2-3” rise for same reason.
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Elbows
• Flat 90, 45: wide dimension turns
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• Vertical 90/45: skinny dimension turns
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• Offsets: Navigate around obstructions
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• Transitions: Change dimensions of duct
• Can be Flat One Side or On Center
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• Boston Elbow: Used for return drops
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• Filter Boot: Flanged to attach to side of furnace or
filter housing
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• Tee
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• Pair of Pants:
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Ductmate/ TDC
• Alternative to slip and drive connections
• Flange attached to duct ends so it can be bolted together
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Prefabricated Fittings
• Typically used for branch runs
• Round Pipe: Used in floor bays
• Oval Pipe: Used inside wall cavity
• Stack Duct: Rect. Duct used inside wall-2 ¼” or 3 ¼”
thick
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• Round Elbows: Can be turned from 0 to 90 degrees
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Takeoffs:
Can be Air tight (attics, crawl)
or Adjustable Clinch type (basements)
Top, Side, W/ or W/out Damper
Square to round (prefer) or round collar.
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Ceiling Boxes
• Top Box or Side Outlet
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• Hand Damper: adjust and balance airflow
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Register Boots
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Terminate in floor or wall
90 boot
End Boot
Straight Boot
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Oval Fittings
• Elbows:
• Vertical and Flat 90’’s/45’s
• Oval to round
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Oval Fittings
• Stack head fitting: Terminates in wall for register
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• Toe kick: under cabinets
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Duct sealing
• Necessary to prevent loss of heating/cooling
capacity to un-conditioned spaces.
• Code enforcement: Some towns require
pressure test for ductwork.
• Problem spots:
– Plenum/takeoff connections,
– end caps,
– pipe seams,
– joints
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• Foil Tape: (use spreader)
• Mastic: Usually applied with a paint brush
• Butyl Tape: Seals like mastic, less messy,
adheres like glue.
• Caulking: Silicone, mastic
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