Gas Connection; Leak Check; Start-Up Operation - Mr. Heater MHU 45 Operating Instructions And Owner's Manual

NOTE The MHU/HSU series unit heaters use a direct spark
ignition system. There is no pilot necessary as the spark lights the
main burner as the gas valve is turned on. The direct spark ignition
control board emits radio noise as the sparking process is
underway. The level of energy may be sufficient to disturb a logic
circuit in a microprocessor controlled thermostat. It is
recommended that an isolation relay be used when connecting
the unit heaters to a microprocessor controlled thermostat. Install
the thermostat according to instructions provided. Select circuit
protection and wire size according to the unit rating plate. Install a
separate disconnect switch (protected by either fuse or circuit
breaker) near the unit so that power can be turned off for
servicing. Connect wiring through knockout on the junction box
located on the side of the unit heater. Refer to heater wiring
diagram for connection information. Use 18 gauge wire or larger
for thermostat connections.
Electrically ground unit in accordance with local codes or, in the
absence of local codes, in accordance with the current National
Electrical Code (ANSI/NFPA No. 70) in the U.S.A., and in Canada
with the current Canadian Electrical Code, Part 1 CSA C22.1.
NOTE Uninsulated ground wires must be wrapped in electrical
tape to avoid damage to the electrical system.
Make line voltage connections as shown in figure 7. Connect
field wiring as shown on wiring diagram on unit. Also refer to
typical diagram in this manual. An additional thermostat wire must
be run to terminal "G" on heater when continuous blower is
desired.

GAS CONNECTION

When connecting gas supply, the length of the run from the
meter must be considered in determining the pipe size to avoid
excessive pressure drop.
A line pressure of 7" w.c. (178mm w.c.) for natural gas should be
maintained when sizing piping. A line pressure of 13" w.c. (330mm
w.c.) should be maintained for liquefied petroleum (LP) gas.
For correct sizing of piping, refer to the (American) National Fuel
Gas Code ANSI Z223.1 or (Canada) CSA B149.1, Natural Gas and
Propane Installation Code or consult the utility having jurisdiction.
A drip leg should be installed in the vertical pipe run to the unit. In
some localities, codes may require that a manual main shutoff
valve and union (furnished by installer) be installed external to the
unit. Union must be of the ground joint type. A drip leg should be
readily accessible to permit cleaning and emptying. See figure 8.
NOTE If a switch box is mounted over electrical knockouts on back
of unit, leave a minimum of 4" (102mm) clearance between switch
box and drip leg.
A 1/8" NPT plugged tap shall be installed immediately upstream of
the gas supply connection to the heater.
NOTE Compounds used on threaded joints of gas piping must be
resistant to the actions of liquefied petroleum gases.

LEAK CHECK

After gas piping is completed, carefully check all piping
connections, (field and factory), for gas leaks. Use a soap
solution or other preferred means.
11
Enerco | Compact Unit Heater
CAUTION DO NOT use matches, candles, flame or other sources
of ignition to check for gas leaks.
IMPORTANT The heater and its individual shut off valve must be
disconnected from the gas supply piping system during any
pressure testing of that system at test pressures in excess of 1/2
psig (3.45kPa).
The appliance must be isolated from the gas supply piping system
by closing its individual manual gas shutoff valve during any
pressure testing of the gas supply system at test pressures equal
to or less than 1/2 psig (3.45kPa). See figure 9.
NOTE In case emergency shutdown is required, shut down main
gas valve and disconnect main power to unit. These devices should
be properly labeled by the installer.
START – UP AND OPERATION
UNIT START–UP
FOR YOUR SAFETY READ BEFORE LIGHTING
BEFORE LIGHTING smell all around the appliance area for gas. Be
sure to smell next to the floor because some gas is heavier than
air and will settle on the floor.
Use only your hand to push in or turn the gas control knob. Never
use tools. If the knob will not push in or turn by hand, do not try to
repair it, call a qualified service technician. Force or attempted
repair may result in a fire or explosion.
MHU45/75 and HSU45/75 unit heaters are equipped with an
automatic spark ignition system. There is no pilot. In case of a
safety shutdown, move thermostat switch to OFF, then return the
thermostat switch to HEAT position.
Should overheating occur, or the gas supply fail to shut off, shut
off the manual gas valve to the appliance before shutting off the
electrical supply.
GAS VALVE OPERATION FOR ROBERTSHAW
2000DER SERIES VALVE (FIGURE 10)
1. STOP! Read the safety information at the beginning of this
section.
2. Set the thermostat to lowest setting.
3. Turn off all electrical power to appliance.
4. This appliance is equipped with an ignition device which
automatically lights burner. DO NOT attempt to light the
burners manually.
5. Depress knob on gas valve; knob will snap to OFF.
(See Figure 10)
6. Wait five minutes to clear out any gas. If you then smell gas,
STOP! Immediately call your gas supplier from a neighbor's
phone. Follow the gas supplier's instructions. If you do not
smell gas go to next step.
7 . Turn knob on gas valve 90
8. Turn on electrical power to unit.
9. Set the thermostat to desired setting.
10. The combustion air blower will start. The burners will light
within 40 seconds.
Operating Instructions and Owner's Manual
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counterclockwise to ON.
04/07 Revision B #60016