3.9 Gas piping
Note
Due to the precision of modern modulating boilers it is important to pay special attention to
gas pressure regulation.
Important: Check gas supply pressure to each boiler with a manometer or other high-
quality precision measuring device. Pressure should be monitored before firing the boiler,
during operation throughout the boiler's full modulation range, and after the call when the
regulator is in a "lock-up" condition.
Pay special attention to retrofit situations where existing regulators may have an over-sized
orifice and/or worn seats, causing pressure “creep” and high lock-up pressures.
A high quality regulator will maintain constant pressure above the boiler’s minimum
specification at all firing rates, and will not exceed the boiler’s maximum pressure rating
when locked-up with no load.
3.9.1 Gas pressure
The boilers require a minimum inlet gas supply pressure of 4.0" w.c. for natural gas or propane
during high fire operation. For either fuel, the inlet pressure shall be no greater than 14.0" w.c.
Confirm this pressure range is available with your local gas supplier.
The inlet gas connection to the boiler is 1" NPT (female).
The high gas pressure switch setpoint is set at 14" wc and the low gas pressure setpoint is set at
3.5" wc. To locate the switches on the boiler, see Figure 42 or Figure 43 .
Adequate gas supply piping must be installed with no smaller than 1¼" Schedule 40 (e.g. Iron Pipe
Size (IPS) and using a 1" w.c. pressure drop, in accordance with the following chart.
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