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 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 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 not to exceed the unit
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
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.
• This unit is not supplied with air filter(s) and has no factory
equipped means for accommodating internal filter(s). A
suitable air filter must be installed upstream of the evaporator
coil of the return air system. Refer to
for recommended
filter sizes.
• 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.
• Horizontal and downflow 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.
Table 1. Air Filter Requirements
NOMINAL
COOLING
(TONNAGE)
APPROXIMATE
AIR FLOW
RANGE (CFM)
APPROXIMATE
FILTER AREA
(SQ. IN.)*
RECOMMENDED
FILTER SIZE
(IN. x IN.)
2
700 - 900
450
20 x 25
3
1,000 - 1,300
625
25 x 25
4
1,500 - 1,900
915
18 x 25 (2 required)
5
1,600 - 2,000
975
20 x 25 (2 required)
* Based on velocity of 300 ft/min for disposable filters.
