Adding a Gas Appliance? Ask for the Load Calculation First

First, the thing that is not optional

If you ever smell gas, stop and leave the building. Do not operate light switches either way, do not use a phone indoors, and do not go looking for the source or hunting for a valve if that means staying inside longer.

From somewhere safely away from the property, call the emergency line for Puget Sound Energy, which is the natural gas provider across this area, and call the fire service. That call comes before any plumber, including us.

Our part starts afterwards, once the people whose actual job this is have made the supply safe. If any company suggests you go hunting for the source before those two calls have been made, that suggestion alone tells you enough about them.

Everything else on this page is about planned work, where there is time to do it properly.

Why the answer is so often no, or not yet

Any gas installation is dimensioned around the total draw expected of it on the day it goes in. Diameters get selected so every connected appliance can pull what it needs at the same moment without pressure falling under the minimum any one of them will tolerate.

Picture what that meant when a Federal Way house went up in 1985. Whoever specified the pipework was working to a furnace, a storage water heater, and perhaps a cooker or a dryer. Nobody had reason to build in spare capacity for equipment that had not been invented, and nobody was going to pay for oversized pipe the property did not need.

Four decades on, someone wants a generator, a fire pit or a high draw heater, and the truthful opening answer is that nobody can say until the sums have been done. Quite often the run to the appliance falls short. Sometimes the culprit is the leg feeding that half of the building. Now and then the meter itself will not deliver the combined load once the new item joins the list.

Each of those is a different scale of work. The third involves the utility rather than just a contractor.

What the calculation actually considers

It is not mysterious and any competent contractor can walk you through it.

Every gas appliance has a rated input, published by the manufacturer, expressed as an energy figure per hour. The calculation adds up everything connected to the system, including whatever you want to add.

Then it looks at the pipe. Carrying capacity depends on internal diameter and on the length of the run, because pressure is lost along the way. A pipe that comfortably supplies an appliance ten feet from the meter may not supply the same appliance forty feet away. Branches complicate it further, since each section carries only what is downstream of it.

Finally it checks the meter and the delivery pressure, because the pipe can only distribute what is arriving in the first place.

The output is a straightforward yes, a yes with specified pipe upsizing, or a no without utility involvement. Ask to see it. A contractor who cannot produce the reasoning has not done the assessment, whatever number they have quoted.

One nuance worth understanding, because it explains results that otherwise look odd. The calculation is normally done against everything running at once, which is deliberately pessimistic, since a household rarely fires the furnace, the cooker, the dryer and the water heater simultaneously. Some appliances are treated differently on the reasonable basis that they will not coincide. That is a legitimate engineering judgement rather than a shortcut, and if a contractor has made one it is fair to ask them to say which appliances they assumed would not run together and why.

The four requests, and what each really depends on

A gas range in a kitchen that has always been electric. The demand is moderate, so this is usually about route rather than capacity. The question is where the nearest adequate line runs and how to get from there to the kitchen without unreasonable disruption.

A high demand water heater. This is the one where capacity most often bites, because heating water on demand requires a very large burst of gas the instant a tap opens rather than a steady modest draw. That constraint is covered in more detail in the piece on why tankless quotes come in high.

An outdoor kitchen or fire feature. Route, materials and depth for any buried section, plus permitting. Buried gas piping is its own specification and it is not a place for improvisation.

A standby generator. This is the one people most underestimate, because a generator draws sustained load at the same time as the rest of the house, and it does so during exactly the conditions when everything else is also running. The total connected load calculation matters more here than anywhere else on the list.

Why this is not work to informalise

Gas piping in this state is governed by the state code, and the consequence of getting it wrong sits in a different category from the consequence of getting a drain wrong. A poor joint on a waste line produces a smell and a mess. A poor joint on a gas line produces something else.

Pressure testing is what unofficial work leaves out more than anything else. Before a new run carries any gas it should be brought up to pressure and watched, and passing that watch is what separates pipework somebody reckons is fine from pipework that has proved it. Ask whether the test is in the price and ask what the reading was.

Earthquakes come into it too. The ground here moves, and the thinking that produces strapping rules for a hot water tank carries straight over into how gas pipe gets held up and where a flexible connector is and is not appropriate.

And unpermitted gas work is genuinely bad to discover during a property sale or an insurance claim, which are the two moments it reliably surfaces. What proper gas line work involves is set out on the service page.

Two things worth checking on what you already have

Flexible appliance connectors have a service life, and older uncoated brass connectors have been the subject of long standing safety concerns. If an appliance is being moved for any reason, replacing its connector at the same time is a small cost against a real risk.

And look at the condition of exposed piping, particularly in the crawl space, which is the same space a leak investigation would take somebody into. Black iron is durable but it is not immune to time, and this is a wet region with a long damp season, which is harder on metal than a dry climate would be. Corrosion at points where piping passes through a wall or a slab, and at buried transitions, is worth looking at rather than assuming.

Neither of those is urgent in the way a gas smell is. Both are the kind of thing worth mentioning to a contractor who is already on site for something else.