Gas Line for a New Commercial Appliance

Every gas system has three ceilings, and a new appliance can hit any of them first.

1. 1The pipe. Each section of pipe carries a set volume over a set length. The fuel gas code's sizing tables show how fast that falls off: at standard pressure, Table 402.4(1) rates 1-inch steel at 215 cubic feet per hour over 50 feet but only 148 over 100 feet.
2. 2The meter. Southwest Gas owns the meter and sized it for the load you had when it was set. Its Central Arizona commercial package lists capacities by model; an AL 425, for example, is rated for 425 cubic feet per hour at standard delivery pressure.
3. 3The pressure under load. Even if the math looks fine, a long or restricted line can drop pressure when everything fires at once.

Natural gas carries roughly 1,000 Btu per cubic foot for sizing, so a 199,000 Btu water heater adds about 199 cubic feet per hour. Southwest Gas's tariff puts the average heating value at not less than 900 Btu per cubic foot, so when the margin is close we use the utility's number.

The question comes up anywhere a business adds gas equipment:

• Water heaters and boilers going up in size, or a tank swapped for a high-input tankless unit. See whether a bigger commercial water heater needs a bigger gas line.
• Laundromat and hotel laundry dryers, where a new bank of dryers can double a building's load. Our laundromat plumbing page covers the rest of that building.
• Standby generators, which Glendale requires to have a separate gas pipe of their own, and which the fuel gas code says can never be rigidly connected to the piping. See gas lines for commercial generators.
• Patio heaters and fire features on a restaurant patio. See gas lines for patio heaters.
• A new fryer, range or oven on a working cooking line.

We start with what's actually there, not what the drawings from ten years ago say.

Inventory. Every appliance on that meter and its input from the rating plate, plus the new one.

Measure the run. The length from the meter to the farthest appliance, and the pipe size of each section along the way.

Measure the pressure. A.O. Smith's commercial water heater handbook gives the field test: read supply pressure static, then with every appliance on the main firing at full capacity. If it drops more than 1.5 inches of water column as gas starts to flow, the handbook says the supply system, including the gas line or regulator, "may be restricted or undersized."

Read the meter. The model on the meter tells us its rated capacity, which we compare against the new total.

The result is one of three answers. It fits, and you get a new branch. The pipe is short, and a section gets upsized or a dedicated line runs from the meter. Or the meter is the limit, and Southwest Gas has to make a change before the new appliance can run at full fire.

A bigger meter is Southwest Gas's call, not ours. Its tariff says the customer must tell it about load changes, and a larger meter or higher delivery pressure is made at the utility's option, with the customer possibly reimbursing it. Its commercial package adds that a load over 1,000 cubic feet per hour may need a rotary meter designed and built, which takes a minimum of 2 weeks.

That's why we check the meter before you buy the equipment. A wait on a meter change is a scheduling problem if you know about it in advance and a crisis if you find out after the dryers arrive. Our page on getting a bigger Southwest Gas meter covers the request, and 2 psi delivery is the other lever for large loads.

In Phoenix, adding Btu load that requires piping capacity calculations is permit work with a city inspection and a city clearance. The good news is the testing. Section 406.1.3 says only the newly installed branch needs the pressure test, while the joint where it ties into the old pipe is checked with leak-detecting fluid. So the existing system usually stays in service while the new branch is built and tested, with a short shutdown for the tie-in. Other Valley cities set their own test pressures; see commercial gas pressure testing.

If you're replacing an appliance with one of the same or lower input in the same spot, with no piping changes, Phoenix's clearance table says no permit is needed and no capacity check is triggered. That's a kitchen equipment hookup or a straight swap. And a load calculation on paper is something your mechanical engineer or equipment dealer can run first; we're happy to check their numbers against what's in the wall.

We inventory the load, measure pressure under full fire, read the meter, size the new branch or the upsized section, pull the permit, build and test it, and send the clearance to Southwest Gas. We're licensed and insured, and the estimate is free with an upfront price before work starts. Related: commercial gas line service, commercial water heaters and commercial plumbing.