8
• Design the duct work according to Manual D by the Air
Conditioning Contractors of America (ACCA).
• The ducts must be properly sized not to exceed the
units maximum ESP rating at 400 SCFM per nominal
ton of cooling capacity.
• Duct work should be attached directly to the unit flanges
for horizontal applications.
• If a roof curb is installed, the ducts must be attached to
the curb hangers, not the unit.
• It is recommended that the outlet duct be provided
with a removable access panel. The opening should
be accessible when the unit is installed in service and
shall be sizes so that smoke or reflected light may be
observed inside the casing to indicate the presence of
leaks in the heat exchanger. The cover for the opening
shall be attached in a way that will prevent leaks.
• If outside air is utilized as return air to the unit for
ventilation or to improve indoor air quality, the system
must be designed so that the return air to the unit is not
less than 50° F (10° C) during heating operation.
• If a combination of indoor and outdoor air is used, the
ducts and damper system must be designed so that the
return air supply to the furnace is equal to the return air
supply under normal, indoor return air applications.
Unconditioned Spaces
All duct work passing through unconditioned space must
be properly insulated to minimize duct losses and prevent
condensation. Use insulation with an outer vapor barrier.
Refer to local codes for insulation material requirements.
Acoustical Duct Work
Certain installations may require the use of acoustical
lining inside the supply duct work.
• Acoustical insulation must be in accordance with the
current revision of the Sheet Metal and Air Conditioning
Contractors National Association (SMACNA) application
standard for duct liners.
• Duct lining must be UL classified batts or blankets with
a fire hazard classification of FHC-25/50 or less.
• Fiber duct work may be used in place of internal duct
liners if the fiber duct work is in accordance with the
current revision of the SMACNA construction standard
on fibrous glass ducts. Fibrous duct work and internal
acoustical lining must be NFPA Class 1 air ducts when
tested per UL Standard 181 for Class 1 ducts.
• The vent termination must be located at least 3 feet
above any forced air inlet located within 10 feet.
• The vent termination must be located at least 4 feet
below, 4 feet horizontally from, or 1 foot above any
door, window, or gravity air inlet into any building.
• The unit should be installed in a way that prevents any
obstruction of the vent termination during accumulating
snow.
• Verify exhaust gases will not impinge on windows
or building surfaces, which may be compromised or
damaged by condensation.
• Do not install the unit such that exhaust from the vent
termination is directed into window wells, stairwells,
under decks, or in alcoves or similarly recessed areas.
CIRCULATING AIR SUPPLY
WARNING:
Products of combustion must not be allowed to
enter the return air ductwork or the circulating air
supply. Failure to prevent products of combustion
from being circulated into the living space can
create potentially hazardous conditions including
carbon monoxide poisoning that could result in
personal injury or death.
All return ductwork must be adequately sealed,
all joints must be taped, and the ductwork must
be secured to the unit with sheet metal screws.
When return air is provided through the bottom
of the unit, the joint between the unit and the
return air plenum must be air tight.
The roof curb or cement pad that the unit is
mounted must provide sound physical support of
the unit with no gaps, cracks, or sagging bewteen
the unit and pad.
Return air and circulating air ductwork must not
be connected to any other heat producing device
such as a fireplace insert, stove, etc. Doing so
may result in fire, explosion, carbon monoxide
poisoning, personal injury, or property damage.
Air Ducts
This unit is designed only for use with a supply and return
duct. Air ducts should be installed in accordance with the
standards of the National Fire Protection Association
“Standard for Installation of Air Conditioning Systems”
(NFPA 90A), “Standard for Installation of Residence Type
Warm Air Heating and Air Conditioning Systems” (NFPA
90B), and all applicable local codes. NFPA publications
are available by writing to: National Fire Protection
Association, Batterymarch Park, Quincy, ME 02269 or
visit www.NFPA.org on the web.
