10
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 on which the unit is
mounted must provide sound physical support of
the unit with no gaps, cracks, or sagging between
the unit and the curb or pad.
Return air and circulating air ductwork must not
be connected to any other heat producing device
such as a fi replace insert, stove, etc. Doing so
may result in fi re, 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.
• Design the duct work according to Manual D by the Air
Conditioning Contractors of America (ACCA).
• The ducts must be properly sized and not exceed 0.2”
W.C. pressure drop at 400 scfm per nominal ton of
cooling capacity.
• Duct work should be attached directly to the unit fl anges
for horizontal applications.
• If 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 refl ected 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.
Air Filter Requirements
WARNING:
Never operate the unit without a fi lter in place.
Dust and lint could accumulate on internal parts,
resulting in loss of effi ciency, equipment damage
and possible fi re.
• A suitable air fi lter must be installed upstream of the
evaporator coil of the return air system. Refer to Table
1 for recommended fi lter sizes.
• All return air must pass through the fi lters before entering
the evaporator coil.
It is important that all fi lters be kept
clean and replaced frequently to ensure proper operation
of unit. Dirty or clogged fi lters will reduce the effi ciency
of the unit and result in unit shutdowns.
• Air fi lter pressure drop must not exceed 0.08 inches WC.
• Downfl ow Installations require an internal fi lter accessory
kit to be installed.
• Horizontal Installations require the air fi lter system be
installed in the return air ductwork.
NOTE TO INSTALLER: After installing or replacing the
fi ltration system for this unit, add the following statement
on or adjacent to the fi lter service panel: “Replace
fi lter(s) installed in your system only with the same
dimensional size fi lters that are being replaced.”
Table 1. Air Filter Requirements
Nominal
Cooling
(Tons)
Approximate
Air Flow
Range (CFM)
Approximate
Filter Area
(Sq. In.)*
Recommended
Filter Size
(In. x In.)
3.0
1,100 - 1,300
625
25 x 25
4.0
1,400 - 1,800
850
18 x 24 (2 required)
5.0
1,800 - 2,200
1,000
20 x 25 (2 required)
* Based on velocity of 300 ft/min for disposable fi lters and
500 ft/min for high velocity (cleanable) Filters.
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.
