2
ACOUSTICAL CONSIDERATIONS
In order to minimize sound transmitted to the space, please
conform to the following recommendations (see Fig. 1):
Location
• Avoid locating the unit above sound-sensitive areas.
Instead, locate the unit above restrooms, storage areas,
corridors, or other noise-tolerant areas.
• Avoid mounting the unit in the middle of large roof
expanses between vertical supports. This will minimize
the phenomenon known as roof bounce.
• Install the units close to vertical roof supports (columns
or load bearing walls).
• Locate the units at least 25 ft away from critical areas. If
this is not possible, the ductwork and ceiling structure
should be acoustically treated.
• Consider the use of vibration isolators or an acoustic curb.
Ductwork
• Utilize flexible connectors between the unit and the sup-
ply and return ducts.
• Supply and return air main trunk ducts should be located
over hallways and/or public areas.
• Provide trailing edge turning vanes in ductwork elbows
and tees to reduce air turbulence.
• Make the ductwork as stiff as possible.
• Use round duct wherever possible because it is less
noisy.
• Seal all penetrations around ductwork entering the space.
• Make sure that ceiling and wall contractors do not attach
hangers or supports to ductwork.
• Provide as smooth and gradual transition as possible when
connecting the rooftop unit discharge to the supply duct.
• If a ceiling plenum return is utilized, provide a return
elbow or tee to eliminate line-of-sight noise to the space.
Face the entrance of the return duct away from other
adjacent units.
Acoustic Insulation
• Provide acoustic interior lining for first 20 ft of supply
and return duct or until the first elbow is encountered.
The elbow prevents line-of-sight transmission in the sup-
ply and return ducts.
• Install a double layer of 2-in. low density quilted fiber-
glass acoustical pad with a
1
/
8
-in. barium-loaded vinyl
facing on top of the roof deck before building insulation
and roofing installation occur. Place the material inside
the curb and for 4 to 8 ft beyond the unit perimeter,
dependent upon unit size (larger units require a wider
apron outside the curb). Openings in the pad should only
be large enough for the supply and return ducts. An alter-
nate approach is to use two layers of gypsum board with
staggered seams in addition to the acoustical pad.
CAUTION
DO NOT re-use compressor oil or any oil that has been
exposed to the atmosphere. Dispose of oil per local codes
and regulations. DO NOT leave refrigerant system open to
air any longer than the actual time required to service the
equipment. Seal circuits being serviced and charge with
dry nitrogen to prevent oil contamination when timely
repairs cannot be completed. Failure to follow these proce-
dures may result in damage to equipment.
FLEXIBLE
CONNECTORS
SUPPLY AND
RETURN
VIBRATION
ISOLATORS
IN ROOF
CURB
INTAKE
PLENUM
SUPPLY
FAN
DISCHARGE
PLENUM
COMPRESSOR/
CONDENSING
SECTION
ALL ROOF
PENETRATIONS
SHOULD BE
SEALED
AIR TIGHT
ROUND DUCT CONTROLS
RUMBLE BEST
SUPPLY AND RETURN
DUCTS LINED WITH
ACOUSTICAL DUCT LINER
Fig. 1 — Acoustical Considerations
