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57UH-PRC002-EN
Mechanical
Specifications
High Efficiency Propeller and
Centrifugal Fan Gas Unit
Heaters
General
Units are completely factory assembled,
piped, wired, and test fired. All units are
AGA Certified and conform with the
latest ANSI Standards for safe and
efficient performance. Units are provided
with two-point suspension hangers on
propeller fan unit heaters and with four-
point suspension hangers on centrifugal
fan unit heaters. All units are available
for operation on either natural or LP
(liquid propane) gas.
Casing
Casings are die-formed, 20-gauge
galvanized steel and finished in baked
enamel. The bottom panel is easily
removed to provide service access to the
burners, pilot and orifices. The pilot is
also accessible through a side panel
access plate. All units provided with
independently adjustable horizontal
louvers with stops to prevent total
closure.
Heat Exchanger
Standard heat exchanger construction
consists of seam welded 20-gauge
aluminized steel tubes and 18-gauge
aluminized steel headers.
The heat exchanger, burner and draft
hood assembly carry a non-prorated
warranty to be free from defective
material and workmanship for a period
of ten years from date of manufacture,
excluding loss due to misuse,
negligence, or corrosion by chemicals
precipitated in the air.
Burners
Burners are die-formed, corrosion
resistant aluminized steel, with stainless
steel port protectors. Port protectors
reduce scale or foreign matter from
obstructing the burner ports. Burners
individually removable for ease of
inspection and servicing. Each burner is
provided with an individually adjustable,
manually rotated air shutter adjustment.
Fans
Fan blades are constructed of aluminum
with an aerodynamic contour. All fans
are dynamically balanced for quiet,
efficient operation and supplied with a
protective type fan guard. Rubber-in-
shear isolators provide isolation
between the fan/motor combination and
the unit heater casing.
All Motors
Standard motors are 115V, 60 Hz, single
phase, open drip-proof with built-in
thermal overload protection.
Optional Fan Unit Motors
All motors are 115V, 60 Hz, single phase
totally enclosed with built-in thermal
overload protection and permanently
lubricated bearings.
Controls
A factory installed junction box is
provided for all power connections.
Standard units are provided with a 24V
combination single stage redundant gas
valve, consisting of a combination pilot
solenoid valve, automatic electric gas
valve, pilot filter, pressure regulator, pilot
adjustment and manual shutoff. A flue
vent fan relay and combustion air
proving switch is also provided as
standard. Standard equipment includes
spark-ignited intermittent pilot system
with electronic flame supervision. A 24V
control transformer, high limit and fan
time delay relay are provided. The fan
time delay relay delays the fan start until
the heat exchanger reaches a
predetermined temperature. It also
allows the fan to operate after burner
shutdown, removing residual heat from
the heat exchanger.
Two-Stage Gas Valve
(N/A on 30-75 MBh units)
Provides two stages of heat. Ignition is at
low fire (50% of the furnaces rated input).
Requires the use of a two-stage
thermostat.
Hydraulic Modulating Gas Valve
(N/A on 30-75 MBh units)
Provides modulated heat output. Ignition
is at low fire (50% input) and discharge
temperature sensing bulb located in the
air stream modulates the gas input from
100% to 50% rated input. Provided with
an automatic electric valve in series
which cycles the unit in response to a
low voltage single-stage thermostat
(thermostat not included).
Hydraulic Modulating Gas Valve with
Bypass
(N/A on 30-75 MBh units)
An additional electric valve in parallel
bypasses the hydraulic modulating
valve, overriding the discharge
temperature sensing bulb, allowing full
fire. Requires the use of a separate
thermostat to control the electric valve.
Electronic Modulating Gas Valve (Natural
Gas Units Only)
(N/A on 30-75 MBh units)
Provides modulated heat output. Ignition
is at full fire (100 percent input), and
modulates the gas input from 100 to 50
percent rated input. Available for use
with room thermostat or duct thermostat
with remote setpoint adjustment. Duct
thermostat available with optional
override room thermostat which causes
the unit to go to full fire when the room
temperature falls below the override
room thermostat.
Electronic Modulating
4-20 mA/0-10VDC Input
Provides modulated heat output. Ignition
is at full fire (100 percent input), and
modulates the gas input from 100
percent to 40 percent rated input.
The modulating gas valve shall operate
in response to a 4-20 mA or a 0-10 VDC
input from an external DDC control.
Flue Vent Fan
Flue vent fan provides power venting.
Provided factory assembled to a sealed
flue collection chamber. The flue vent fan
is activated in response to a low voltage
(24V) single-stage thermostat (NOTE:
thermostat must be ordered.) A
combustion air pressure switch is
provided as standard to verify proper
powered vent flow prior to allowing the
gas valve to operate.