CFC-E Installation Manual
Part No. 750-459 1-13
1.5.5 - Gas Supply Pipe Sizing
For proper operation of a single unit or a multiple unit installation, we recommend that the gas piping
be sized to allow no more than 0.3" w.c. pressure drop from the source (gas header or utility meter) to
the final unit location. Higher supply pressure systems may allow for a greater pressure drop. In ALL
cases, minimum supply pressures must be met for proper operation of the boiler(s). The gas supplier
(utility) should be consulted to confirm that sufficient volume and normal pressure are provided to the
building at the discharge side of the gas meter or supply pipe.
For installations of new boilers into an existing building, gas pressure should be measured with a
manometer to ensure sufficient pressure is available. A survey of all connected gas-using devices
should be made. If appliances other than the boiler or boilers are connected to the gas supply line, then
a determination must be made of how much flow volume (cfh) will be demanded at one time and the
pressure drop requirement when all appliances are firing.
The total length of gas piping and all fittings must be considered when sizing the gas piping. Total
equivalent length should be calculated from the utility meter or source to the final unit connection. As a
minimum guideline, see gas piping tables below. The data in these tables is from the NFPA 54 source
book, 2006 edition.
To verify the input of each device that is connected to the gas piping, obtain the btu/hr input and divide
this input by the calorific value of the gas that will be utilized. For instance, a unit with 750,000 btu/hr
input divided by a gas calorific value of 1060 will result in a cfh flow of 707. The single boiler is
approximately 20 feet from the gas supply header source. And with a measured gas supply pressure
of 10" w.c. we find from Table 1-6 that a supply pipe size of 1-1/4” should be used as a minimum.
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