Permanent Fuel Line Installation for Standby Generator
Why this matters
The fuel supply system is the largest single point of failure outside the generator itself. A standby generator on natural gas needs a properly sized, well-installed, and code-compliant gas line from the meter to the generator. Undersized lines, leaks, or poor installation result in the generator running poorly or not at all during an outage. This article covers the installation procedure, but it's important to note that the work requires a licensed plumber / gas fitter in most jurisdictions. The pest control / electrical / generator company doesn't perform this work - the fuel line install is a coordinated handoff to the gas trade.
When to use this procedure
- New standby generator installation requiring permanent gas line
- Upgrading from undersized existing line
- Replacing a damaged or leaking line
- Adding generator to existing gas service (often requires utility coordination)
Tools and materials
- Pipe wrenches (multiple sizes)
- Pipe cutter
- Pipe threading set (manual or power)
- Pipe dope OR Teflon tape (gas-rated only)
- Pipe schedule appropriate to the application
- Drip leg components (T fitting, plug)
- Manual shutoff valve (full-port ball valve)
- Pressure regulator (if needed for the generator's pressure spec)
- Pressure gauge for testing
- Leak detection solution (soap solution for testing)
- PPE: eye protection, gloves
- Excavation tools (for buried line)
Safety
Gas line work is regulated. Most jurisdictions require a licensed plumber, gas fitter, OR specifically a Master Plumber with gas endorsement. Performing this work without the appropriate license is a code violation and creates significant legal exposure. The work involves:
- Open flame and natural gas (explosion hazard if leaks)
- Regulated gas pressure (gauges, regulators, code-required venting)
- Pressure testing (safety considerations during the test)
- Permit and inspection (gas system permits are typically required)
Refer the fuel line install to a licensed professional. This article is for the generator service company to understand what the gas fitter does, what to look for during the install, and how to coordinate.
Gas line sizing
The single most important specification: the gas line must deliver the required volume at the required pressure.
For natural gas, generator manufacturers specify:
- BTU consumption at full load (e.g., 250,000 BTU/hr for a 22 kW generator)
- Required gas pressure at the generator inlet (typically 5-11 inches water column / "WC)
- Maximum equivalent length (the longest run the gas line can support at the given diameter)
Pipe sizing depends on:
| Variable | Range |
|---|---|
| Total gas demand | Generator's draw plus any other gas appliances on the same line |
| Pressure available | Utility's supply pressure |
| Pipe diameter | 3/4 inch, 1 inch, 1-1/4 inch, larger |
| Total equivalent length | Straight pipe + 90° bends (each bend = ~2-5 feet) |
A typical calculation:
- 22 kW Generac generator: 250,000 BTU/hr demand
- Distance from meter to generator: 50 feet straight + 4 bends = ~60 feet equivalent
- Available pressure: 7" WC delivered from meter
- Pipe sizing from manufacturer's chart: typically 1-1/4 inch black iron pipe
Undersized pipe is the #1 fuel supply failure mode. Specify generously rather than tightly.
Materials options
| Material | Use |
|---|---|
| Black iron pipe (galvanized OK in some jurisdictions) | Standard above-ground installation |
| CSST (Corrugated Stainless Steel Tubing, e.g., Gastite, OmegaFlex) | Flexible inside walls, faster install; specific bonding requirements per NEC 250.104(B) |
| Polyethylene (PE) pipe with tracer wire | Underground; specific code requirements; needs riser to transition above ground |
| Copper (Type L) | Some jurisdictions allow for gas; verify code |
Each material has installation specifics:
- Black iron: threaded fittings; pipe dope or gas-rated Teflon tape on threads
- CSST: proprietary fittings; bonded with #6 AWG copper to grounding electrode per NEC
- PE: heat-fused or compression fittings; transition fittings to metal for risers
Connection to the gas meter
The line starts at the gas meter:
- Coordinate with the utility - some require utility presence for meter-side connections
- Verify the meter is sized for the additional load (the utility upgrades the meter if needed)
- Verify the regulator is sized appropriately
- Some installations require a separate utility meter for the generator (commercial)
Drip leg / dirt leg
Required by code at the generator's gas inlet:
- T-fitting installed near the generator
- Vertical drop pipe (typically 4-6 inches long) closed with a plug at the bottom
- Captures any water condensate or debris before it reaches the generator
- Required per fuel gas code (IFGC 408.4)
A missing drip leg is a common code violation found at inspection.
Manual shutoff valve
Required by code:
- Full-port ball valve immediately upstream of the generator's gas inlet
- Accessible without tools
- Marked / labeled
- Used during service and emergency shutoff
This is a critical safety device. Verify it operates smoothly during install and at every service visit.
Pressure regulator (if needed)
Some installations need a secondary regulator:
- Utility meter delivers a specific pressure (often 7" WC residential, higher commercial)
- Generator may need lower pressure (typical Generac residential: 5-7" WC)
- Secondary regulator drops the pressure to the generator's spec
The regulator must be:
- Rated for the gas type and pressure
- Listed for outdoor use (most gas regulators)
- Vented per the manufacturer (vent termination per IFGC)
Pressure testing
After installation, the system is pressure tested:
- Connect a pressure gauge to the system
- Pressurize to the test pressure (typically 1.5x the operating pressure, OR the code-specified test pressure)
- Hold for the test duration (typically 15 minutes to 2 hours per code)
- Verify no pressure drop
- Document the test result for the inspector
The test must be witnessed by the inspector in most jurisdictions, OR documented by the licensed installer with their signature.
Leak detection at the connections
After pressure test passes and gas is restored:
- Brush soap solution on every connection
- Bubbles indicate leakage
- Re-tighten and re-test
- Don't trust untested connections - even pressure-tested systems can develop leaks at threads
Underground line installation
For buried lines:
References
- IFGC (International Fuel Gas Code)
- NFPA 54 (National Fuel Gas Code)
- NFPA 58 (Liquefied Petroleum Gas Code)
- NFPA 37 (Stationary Combustion Engines)
- NEC 250.104(B) (CSST bonding)
- ASME / ANSI Z21.21 (Connectors and Tubing for gas appliances)
- State / local gas codes
- Manufacturer documentation (Generac, Kohler, etc.)
- Manuall internal: Whole House Generator Install, Codes and Permits, Generator Natural Gas Conversion