What size gas line does a Rinnai Tankless Water Heater require?

Rinnai Tankless water heaters are designed to provide maximum performance and efficiency using either a 3/4" or 1/2" gas line, as long as sufficient gas flow is available. An undersized gas line can stress a tankless system and possibly reduce its lifespan, all Rinnai tankless water heaters are equipped with technology that safely ceases operation if they detect an inadequate gas flow. This innovative feature safeguards the unit from compromising performance and efficiency.

The table below lists the maximum length for both 1/2" and 3/4" gas lines when paired with Rinnai tankless water heater models.  


Rinnai Tankless Water Heater Models
Name Plate Ratings (BTU/H)
SCH 40 Metallic Pipe Size (Maximum Equivalent Length)
1/2 Inch
3/4 Inch
V53e 120,000 100' 450'
V65e, V65i 150,000 70' 300'
RUC80i, RU80i 152,000 70' 166'
RL75i, RL75e 180,000 50' 200'
V75i, V75e 180,000 50' 200'
RLX94i 192,000 40' 175'
RUC98i, RU98e 199,000 40' 175'
RL94i, RL94e 199,000 40' 175'

INTENDED USE: Initial Supply Pressure: 8.0" w.c. or greater; Inlet Pressure: <2 psi; Pressure Drop: 3.0" w.c.; Specific Gravity: 0.60

Source: NFPA 54/ ANSI X223.1 National Fuel Gas Code


Here are the steps needed to properly size your gas line:

  • Determine what type of gas is being used
  • Determine inlet pressure
  • Determine the allowed pressure drop
  • Determine what other types of gas appliances are sharing the gas line
  • Determine the maximum loads expected on the whole system as stated in the National Fuel Gas Code

For complete information on gas sizing for Rinnai tankless water heaters, consult the 'Operations and Installation Manual' that comes with your unit. Or, consult a licensed Rinnai installation professional who can help guide you through the process.


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