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 0.30 inches
WC pressure drop per 100 feet of equivalent duct 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 duct supports, 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.
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.
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.”
Table 1. Recommended External Air Filter Sizes
EXTERNAL FILTER SIZES
NOMINAL COOLING
(TONNAGE)
FILTER SIZE
(IN. X IN.)
APPROXIMATE AIR FLOW
RANGE (CFM)
APPROXIMATE FILTER
AREA (SQ. IN.)*
2.0
20 x 25
600-900
450
2.5
20 x 30
750-1200
550
3.0
25 x 25
1100-1300
625
3.5
24 x 30
1200-1600
750
4.0
18 x 24 (2 required)
1400-1800
850
5.0
20 x 25 (2 required)
1700-2200
1000
INTERNAL FILTER SIZES
CABINET
HEIGHT
OUTDOOR
FAN DIAMETER
FILTER SIZE
(IN. X IN.)
APPROXIMATE AIR FLOW
RANGE (CFM)
APPROXIMATE FILTER
AREA (SQ. IN.)*
30”
20
(2) 14”x25”
700 - 1300
700
24”
(1) 12”x20” and (1) 16”x25”
640
34”
20
(2) 16”x25”
900 - 1400
800
24”
(1) 12”x20” and (2) 10”x25”
740
38”
20”
(2) 18”x25”
1100 - 1600
900
24”
(1) 12”x20” and (2) 12”x25”
840
42”
20”
(2) 20”x25”
1300 - 1800
1000
24”
(1) 12”x20” and (2) 14”x25”
940
* Based on velocity of 300 ft/min for disposable filters.
