Key takeaway
Gas pipe is sized from appliance demand, pressure, material and the complete route—not by copying the old pipe diameter.
Safety and jurisdiction
Gas installation, modification and pressure testing are qualified-professional work, not a DIY project. If you smell gas or hear a suspected gas leak, leave immediately without operating switches, flames or phones inside. Call 911 and the gas utility from a safe location. Do not re-enter or restore service yourself.
Codes and permit rules vary by city and change over time. Confirm requirements with your local building department and a licensed contractor.
01Know which side of the meter is involved
People often say 'main gas line' when they mean the customer-owned house piping downstream of the meter. Utility mains, service lines and meters have different ownership and authorization requirements. A contractor and the utility should establish that boundary before any work is proposed.
A larger appliance can affect more than its short branch connection. The meter, regulator and shared upstream piping may need review. Never assume that a connection capable of running an old appliance can supply a new tankless heater or several appliances at once.
02Ask for a load and route calculation
A proper design accounts for appliance nameplate input, all relevant connected loads, developed pipe length, fittings, gas type, available pressure and allowable pressure drop. Tables for one material or pressure regime cannot simply be applied to another.
Roseville's California guidance illustrates the kind of submittal to expect: pipe segments, lengths, diameters, materials and appliance BTU ratings. It is a useful explanation of the design process, not a permit approval for Santa Ana or Irvine. Your local authority and gas supplier set the applicable requirements.
03Buried materials need local approval
Buried piping needs the correct listed material, corrosion protection where applicable, approved transitions and means of locating the route as required. Underground gas-rated polyethylene is not ordinary water pipe and is not a general-purpose indoor gas material.
Irvine publishes specific local underground-piping amendments. A material accepted in another California city may not be accepted in the same location in Irvine. Utility locating, safe excavation, separation and authorized connection work must be planned before digging.
- Utility versus customer responsibility identified
- Appliance loads and full route documented
- Meter capacity and local material approvals verified
- Required permit, rough inspection and final approval included
04Testing and putting the line into service are separate
An inspection test checks the piping under a controlled, prescribed condition. It is not the normal pressure supplied to an appliance, and a passing test does not authorize an unqualified person to open valves or restore service.
The qualified installer must protect or isolate equipment as required, complete the approved test, and coordinate inspection and safe commissioning with the authority and utility. Ask for the inspection record and equipment commissioning documentation—not just a picture of a gauge.
Sources and further reading
- City of Roseville — 2025 Gas Piping Information (opens in new tab)A California jurisdiction example, not Santa Ana or Irvine approval. Includes sizing submittals and its 10 psi / 15-minute inspection test.
- City of Irvine — Building Codes and Standards (opens in new tab)2025 standards apply to new plan review applications from January 1, 2026; local amendments matter, particularly for underground piping.
- 2025 California Plumbing Code — chapter directory (opens in new tab)Code reference, not a substitute for the edition and amendments applicable to your permit. Detailed sections may require an account.