Why the appliance is the easy part
When people plan to add a gas range, a tankless water heater, a gas dryer or a fireplace, they focus on the appliance, and understandably so, it is the visible, exciting part. But the appliance is the easy part. The question that actually decides whether it works is whether the gas line feeding it can deliver enough gas, at enough pressure, to run it alongside everything else already on the system. Get that wrong and the shiny new appliance underperforms or does not run right at all.
This is why a good gas line job starts with a load calculation, not a trip to buy pipe. Every gas appliance has a demand rating, and the line has to be sized to carry the total load of everything that might run at once, over the actual distance from the meter, without the pressure dropping too far. It is a real calculation with real numbers, and it is the step a rushed install skips, which is how you end up with a range that will not reach high heat when the water heater is also firing.
| Adding | Why the line matters |
|---|---|
| Tankless water heater | High peak demand often needs the line upsized |
| Gas range / cooktop | Must run at full output alongside other appliances |
| Gas dryer | Adds to the total load the line must carry |
| Converting from electric | New line, sizing and venting from scratch |
| Second big appliance | System sized for the original load may not feed it |
The tankless catch specifically
The appliance that most often surprises people here is the tankless water heater, because its gas demand is deceptively high. A tankless does not sip gas steadily like a tank; it fires a large burner hard the moment you open a hot tap, drawing a high peak that is often more than the existing line was ever sized to deliver. That is why so many tankless installs require upsizing the gas line, and why a quote that ignores the line is not a real quote.
Starve a tankless of gas and it cannot hit its rated output: it runs lukewarm, short-cycles, or throws errors, and the homeowner blames the unit when the real problem is the line. The same principle applies to adding a second big appliance to a system that was sized for what it originally had. So before committing to a gas conversion or a new high-demand appliance, the honest first question is whether the line and the meter can actually feed it, which a plumber determines with the load calculation, not a guess.
CSST, black iron, and doing it safely
Gas piping is not a place for improvisation, because the failure mode is not a leak of water. Two materials are common: traditional black iron pipe and modern flexible CSST (corrugated stainless steel tubing). Both are fine when installed correctly, but each has requirements. CSST in particular must be properly bonded and grounded so that a nearby lightning strike cannot arc through it and puncture it, a step that gets missed by anyone treating gas like water.
This is exactly why gas work is permitted, pressure-tested and inspected rather than done casually. A proper install sizes the pipe for the full load, uses the right material and fittings, pressure-tests every line before it goes back into service, and gets it inspected. Those are not bureaucratic hoops; they are what stands between a working gas system and a genuinely dangerous one. It is the clearest case in plumbing where cheap and fast is the wrong priority.
What to do (and what to do if you smell gas)
The practical takeaway for a Chapel Hill homeowner planning a gas addition is simple: start with the line, not the appliance. Have a plumber run the load calculation for what you want to add against what you already have, confirm whether the line and meter can feed it or need upsizing, and build that into the plan and the budget from the start. That is how you avoid the disappointment of a new appliance that cannot perform because it is being starved.
And one safety note worth stating plainly, unrelated to any project: if you ever smell gas, a distinct rotten-egg odor, treat it as an emergency. Do not flip switches or hunt for the source; leave the building and call the gas utility from outside first, then a plumber for the repair. Gas safety is not the place to save a phone call. For planned work, the same seriousness is why the load calculation, the correct material, and the pressure test are not optional extras but the actual job.
A final planning note: if you are buying the appliance yourself before the install, it is worth sharing the model with your plumber first, because its BTU rating is exactly the number the load calculation needs. Knowing the demand of the specific unit you have chosen, rather than a generic estimate, is what lets us tell you up front whether your line and meter can feed it or need work. That one piece of information, shared before you commit, is what turns a gas addition from a hopeful guess into a job we can scope accurately.
Questions we get
Sometimes, but only if the line can carry the added load at the right pressure over its length. Many additions, especially a tankless, need the line upsized. A load calculation answers it; connecting first and hoping is how you get an appliance that underperforms.
Because it fires a large burner hard the instant you open a hot tap, drawing a much higher peak than a tank. That peak is often more than the old line was sized for, so it frequently has to be upsized, or the unit runs lukewarm and short-cycles.
Both are fine installed correctly. Black iron is traditional and rigid; CSST is flexible and faster to route but must be properly bonded and grounded for lightning safety. The right choice depends on the job, and correct installation matters more than the material.
Yes. Gas lines are permitted, pressure-tested and inspected because the failure mode is dangerous, not just inconvenient. That process is what stands between a safe system and a hazardous one, so it is not a step worth skipping to save time.
Treat it as an emergency. Do not flip switches or search for the source, leave the building and call the gas utility from outside first, then a plumber for the repair. Gas safety always comes before convenience.
Planning a gas range, tankless or conversion?
We size and run the line correctly first, so your new appliance actually performs.