8
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.
• 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 flanges 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 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.
Air Filter Requirements
WARNING:
Never operate the unit without a filter in place.
Dust and lint could accumulate on internal parts,
resulting in loss of efficiency, equipment damage
and possible fire.
• A suitable air filter must be installed upstream of the
evaporator coil of the return air system. Refer to
• All return air must pass through the filters before entering
the evaporator coil.
It is important that all filters be kept clean
and replaced frequently to ensure proper operation of unit.
Dirty or clogged filters will reduce the efficiency of the unit
and result in unit shutdowns.
• Air filter pressure drop must not exceed 0.08 inches WC.
• Downflow Installations require an internal filter accessory
kit to be installed.
• Horizontal Installations require the air filter system be installed
in the return air ductwork.
NOTE TO INSTALLER:
After installing or replacing the
filtration system for this unit, add the following statement
on or adjacent to the filter service panel:
“Replace filter(s)
installed in your system only with the same dimensional
size filters that are being replaced.”
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.
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 filters and 500 ft/min for
high velocity (cleanable) Filters.
