McQuay IM 987
45
Mechanical Installation
Installing Ductwork
On bottom-supply/bottom-return units, if a McQuay roof curb
is not used, the installing contractor should make an airtight
connection by attaching field-fabricated duct collars to the
bottom surface of either the roof curb’s duct flange or the
unit’s duct opening. Do not support the total weight of the duct
work from the unit or these duct flanges. See
Figure 52
.
Units with optional back return, side discharge, or end
discharge all have duct collars provided. To expose the
discharge duct collars on a side discharge unit, remove the
plenum section access door and the door gasketing.
Use flexible connections between the unit and ductwork to
avoid transmission of vibration from the unit to the structure.
To minimize losses and sound transmission, design duct work
per ASHRAE and SMACNA recommendations.
Where return air ducts are not required, connect a
sound-absorbing T or L section to the unit return to reduce
noise transmission to the occupied space.
Ductwork exposed to outdoor conditions must be built in
accordance with ASHRAE and SMACNA recommendations
and local building codes
.
Figure 52: Installing Duct Work
WARNING
Mold can cause personal injury. Materials such as gypsum wall
board can promote mold growth when damp. Such materials
must be protected from moisture that can enter units during
maintenance or normal operation.
NOTICE
Installer must provide access in the ductwork for
plenum-mounted controls.
Once duct work is installed in units with side discharge, access
to plenum-mounted components is difficult.
U n i t D u c t O p e n i n g
U n i t B a s e
9 . 7 6 "
4 . 5 8 "
R o o f C u r b
D u c t F l a n g e r
i n R o o f C u r b
F l e x i b l e
C o n n e c t o r
D u c t w o r k
