LAARS Mighty Therm LO-NOx VW (Sizes 250/400) - Installation, Operation and Maintenance Instructions - Manual (Page 14)

LAARS Heating Systems Page 14
6. Install a non-restrictive manual gas shutoff valve
for service and safety. Check the local codes.
7. Disconnect the heater and its individual shutoff
valve from the supply gas system during pressure
testing of the system at pressures higher than 1/2
pounds per square inch (psi) (3.4 kilopacals
[kPa]). If the test pressusre is equal to or less than
1/2 psi (3.45 kPa), close the manual shutoff valve
on the heater during the piping pressure test.
8. Gas supply pressures to the heater are listed in
Table 6.
NOTE: The heater and all other gas appliances
sharing the heater gas supply line must be firing at
maximum capacity to properly measure the inlet
supply pressure. Low gas pressure could indicate
an under-sized gas meter and/or obstructed gas
supply line.
9. Do not exceed the maximum inlet gas pressures
specified. Excessive pressure will result in
damage to the heater's gas controls. The
minimum pressure specified is for gas input
adjustment.
10. The correct burner manifold gas pressure is
stamped on the rating plate. The regulator on the
gas valve is preset at the factory, and does not
normally need adjustment.
11. Before operating the heater, test the complete gas
supply system and all connections for leaks using
a soap solution.
Caution
Since some leak test solutions (including soap and
water) may cause corrosion or stress cracking,
rinse the piping with water after testing.
2.8 Electrical Wiring
WARNING
Electrically ground the heater in accordance with
the latest edition of the National Electrical Code,
NFPA 70. In Canada, use the latest edition of the
Canadian Electrical Code CSA C22.2 No. 0. Do not
rely on the gas or water piping to ground the metal
parts of the heater. Often, plastic pipe or dielectric
unions isolate the heater electrically. Service and
maintenance personnel who work on or around the
heater may be standing on wet floors and could be
electrocuted by an ungrounded heater.
1. Check heater wiring and pump for correct
voltage, frequency, and phase. Check to make
sure heater is wired for 120 volts alternating
current (VAC). If 240 VAC, contact local factory
representative or Laars.
2. Wire the heater and pump exactly as shown in the
wiring diagram supplied with the heater. See
Figures 28 through 31 for a typical example of a
wiring diagram.
3. Electrically interlock the pump and heater so the
heater cannot come on unless the pump is
running.
Distance from Gas Meter or Last Stage Regulator
0-100 feet 100-200 feet 200-300 feet
0-30 m 30-60 m 60-90 m
Boiler Nat. Nat. Nat.
Size in. mm in. mm in. mm
250 1¼ 32 1¼ 32 1½ 38
400 1¼ 32 1½ 38 2 51
Notes:
1. These numbers are for natural gas (0.65 Sp. Gr.) and
are based on ½ inch (13mm) water column pressure
drop. Check supply pressure with a manometer, and
local code requirements for variations.
2. Check supply pressure and local code requirements
before preceding with work.
3. Pipe fittings must be considered when determining gas
pipe sizing.
Table 5. Natural Gas,
Pipe Size Requirements.
Supply Pressure Natural Gas
Water Column in. mm
Minimum 6 152
See Rating Plate
Maximum 10.5 267
Table 6. Gas Supply Pressure Requirements.
Figure 25. T-Fitting and Sediment Trap.
MANUAL SHUT-OFF
VALVE
GAS
SUPPLY
INLET
T-FITTING
3" (76 mm)
MIN.
UNION
NIPPLE
CAP
TO
BOILER
INLET
OUT OF
PRODUCTION