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to (-).02" WC, as measured at the 5/16" over fire air tap (See Fig. 12). This tap is provided in the upper
burner mounting plate. To measure the flue draft, punch a small hole in the vent connector pipe as close
to the furnace as possible and always before the draft regulator.
Note: Draft over fire may be positive for high fire applications but not to exceed (+).02" WC.
D. DUCT WORK/AIR CONDITIONING:
If the furnace is used in connection with summer air conditioning (cooling), the furnace should be installed
parallel with or on the upstream side of the evaporator coil to avoid condensation in the furnace heat
exchanger. If the cooling unit is installed with a parallel flow arrangement, dampers or other means used
to control flow of air should be provided to prevent chilled air from entering the furnace. If such a damper
is manually operated, it must be equipped with a means to prevent operation of either unit, unless the
damper is in the full heat or cool position.
The duct system should again follow the current design standard of Air Conditioning Contractors of
America (ACCA) or ASHRAE Fundamentals
volume. The most common location for the A-shaped coil (A
style) is shown in Fig. 8.
Fig 8: Acceptable locations for the air conditioner evaporator coil.
NOTICE: The minimum coil pan clearance for a sectional or drum type heat exchanger is three inches
unless specified otherwise by the individual coil manufacturer.
NOTICE: The minimum return air temperature is 55° F.
Airflow Requirements and Sizing of Duct Work:
The duct system must be sized and installed by a qualified installer or service person, following the
design standards of the Air Conditioning Contractors of America (ACCA) or the American Society of
Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). This furnace has been designed to
operate against a maximum external static pressure of 0.5 in. W.G. This is equivalent to 0.1 in.
W.G. supply, and 0.1 in. W.G. return, and 0.3 in. W.G. for evaporator coil.
1. Supply and return air ducts have to be furnished by the installer and run between the appliance,
which must be installed outdoors, and the interior of the structure the appliance serves. These ducts
must be sealed to the casing of the appliance.