Appliance details
2.10Gas piping & connections 
Before connecting the gas supply, check the rating plate on the right side of the heater to be sure that the heater is rated for the same gas to which it will be connected.
In the United States: The installation must conform with local codes or, in the absence of local codes, the National Fuel Gas Code ANSI Z223.1/NFPA 54.
In Canada: The Installation should conform with CGA B149 INSTALLATION CODES and/or local installation codes.
GAS LINE SIZING
The gas supply piping should be sized according to the Applicable Plumbing Code for a maximum draw of 175,000 BTUH. First determine the effective length of the gas supply line by measuring the actual length of piping, and then adding 5 ft. (1.52m) for every elbow or “T” to the actual length. Use the charts in Fig. 22 to determine the pipe diameter necessary to accommodate the BTU (Wh) demand of the unit. If there are more gas drawing appliances on the line, size according to the maximum amount of BTU (Wh) demand.
Note: It is important that if any flexible gas line is used, above or below ground between the gas supply meter/ regulator and the water heater, that it be sized properly; we recommend the use of
Fig. 20 Vertical venting installation - Masonry Chimney (combustion air piping not being shown)
A condensate trap (drain tee) must be used for any vertical exhaust vent installation. The condensate trap should be positioned as near to the top of the heater as possible.
Inlet gas particle screen
Gas piping
Fig. 21
BInstall a manual gas shut off valve, on the gas supply line.
BThe use of a union when connecting gas pipe to the gas inlet connection is critical, this will facilitate any necessary servicing and cleaning of the inlet gas particle screen.
BFlexible gas line connectors are not recommended because they are commonly undersized and restrict gas flow. Oversize the diameter of any flexible gas line connector if one must be used.
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