Seismic Gas Shutoff and Excess Flow Valves
Why this matters
Two kinds of device can shut a house's gas off with nobody touching a valve, and customers mix them up, techs mix them up, and the confusion shows up as a no-heat call nobody can explain or a tankless install that dies every time the furnace starts. One closes on shaking. The other closes on flow too high for the line, which is what a broken line looks like. They sit in different places, belong to different people, reset differently and are required by different layers of law. A tech who knows which is which can answer the customer's question correctly, recognize a trip, and avoid an install that trips one.
The three devices side by side
| Utility excess flow valve | Seismic gas shutoff valve | Customer-side excess flow device | |
|---|---|---|---|
| Who owns it | The gas utility | The property owner | The property owner |
| Where it sits | In the service line, usually near the tap on the main, underground | On the house piping just downstream of the meter, above ground | At the meter outlet or at an appliance connection |
| What closes it | Flow above its trip point, as from a severed service line | Ground motion past the threshold its standard sets | Flow above its rating, as from a broken connector or pipe |
| Required by | Federal pipeline rules on new and replaced residential service lines | Some local jurisdictions | Some local jurisdictions, sometimes as an alternative to a seismic valve |
| Who resets it | Usually resets itself once the leak is stopped; otherwise the utility | Manual reset by a qualified person after a leak check | Per its listing; many reset once downstream is closed |
| Who may work on it | Utility only | Licensed installer, under permit where required | Licensed installer, under permit where required |
The middle column is a mechanical valve that holds a ball or a weighted latch in a cradle; shaking dislodges it and it drops onto a seat. The two outside columns measure nothing but flow: when flow through them rises above a set point, the pressure drop across the valve snaps it shut.
The federal layer: excess flow valves on service lines
49 CFR 192.383 requires a gas operator to install an excess flow valve on any new or replaced service line to a single-family residence before the line is put into service. Rules adopted in 2017 widened it to branched residential service lines, multifamily buildings and small commercial customers with known loads up to 1,000 standard cubic feet per hour per service. The same section lists exceptions, among them a service line that does not operate at 10 psig or more throughout the year, and it requires operators to notify customers on existing lines that they may ask to have one installed. Who pays for an installation on request is set by your state utility commission's tariffs, not by the federal rule; this is not legal advice, and the utility is the one to ask.
Two things that rule is not. It is not a requirement on the house piping, so it never obligates the plumber or HVAC shop, and an existing service line with no excess flow valve is lawful until that line is replaced. And it does not protect against a leak inside the house of the size a loose fitting produces: a valve set to pass a whole house's peak load will not notice a leak smaller than that load.
The local layer: seismic shutoff valves
No federal rule requires a seismic gas valve. Requirements are local and mostly Californian. Some cities and counties there require one on new construction and on alterations above a size or value threshold their ordinance sets, Los Angeles being the most cited example, and California requires that valves sold or installed in the state meet the certification its Division of the State Architect administers. Outside California, a few jurisdictions in other seismic regions have local requirements; most have none. The consensus performance standard for these valves is ASCE/SEI 25, Earthquake-Actuated Automatic Gas Shutoff Devices, which binds only where a law or ordinance adopts it by reference.
Some jurisdictions accept a listed excess flow device on the house side as an alternative to a seismic valve, on the reasoning that what causes fires after a quake is a broken line flowing gas, and a flow device closes on that whether or not the ground shook. Check what your local ordinance accepts.
What a trip looks like on a service call
Seismic valve tripped. Every gas appliance in the house is out at once, pilots included, and the meter is not turning. There may or may not have been a quake the customer felt: these valves also trip when the piping is bumped hard, by a vehicle backing into the meter set, a kick, or someone hanging something heavy on the pipe. The reset is a lever or knob on the valve, and it is not the first step. With the valve still closed, find out why it tripped. If anyone smells gas, everyone leaves the house, no switches touched, no lights, no phone used inside, and the gas utility is called from outside. If not, check the house piping and appliance connections for anything the event could have moved, then reset per the valve maker's instructions, leak-test the appliance connections you can reach with an approved solution or a detector, and relight every pilot, watching each appliance light and run normally (steady flame, draft established at any draft hood) before you leave. A valve reset with a broken connector downstream refills the house with gas at full line pressure.
Utility excess flow valve tripped. This usually follows a line strike in the yard or a large break, and the house loses gas entirely. The valve is underground and belongs to the utility; nobody else digs for it. Many reset themselves through a small bypass once the downstream leak is closed and pressure equalizes, which can take some minutes. If gas does not return, the call is to the utility.
After a quake. Customers ask whether to shut their own gas off. The utilities' consistent answer: only if you smell gas, hear a hiss, or see the meter dial moving with every appliance off, and once it is off, the utility or a qualified technician restores it and relights. See related: How to Check a House for Earthquake Readiness on a Service Call.
Worked example: the tankless swap that trips a valve
A customer wants to replace a 40,000 Btu per hour tank water heater with a 199,000 Btu per hour tankless unit. The house is on a service line replaced six years ago, so it carries a utility excess flow valve, and it has a seismic valve at the meter. Appliance inputs are off the nameplates; the excess flow valve's sizing is an illustrative figure standing in for what the utility's records actually show.
Convert the load. Natural gas carries roughly 1,000 Btu per cubic foot; local heating value runs a few percent higher, so this is a slightly conservative approximation.
- Furnace 80,000 + tank water heater 40,000 + range 65,000 + dryer 22,000 = 207,000 Btu/h, about 207 cubic feet per hour.
- After the swap: 207,000 minus 40,000 plus 199,000 = 366,000 Btu/h, about 366 cubic feet per hour, an increase of 159 cubic feet per hour, so the new load is roughly 1.8 times the old one (366 over 207).
Compare with what the line was built for. Say the utility sized the excess flow valve for a connected load near the old 207 cubic feet per hour, with headroom to a trip point somewhat above that. On a cold morning with the furnace and the tankless firing together, the house can now draw well above the old connected load. That is the condition an excess flow valve exists to treat as a broken line. The customer's symptom is a tankless that faults with low gas pressure, then the whole house losing gas, with nothing broken anywhere.
Compare with the seismic valve. The seismic valve at the meter also carries a flow capacity, and it was chosen for the old piping. If its rating sits below the new load, it does not trip, but it adds pressure drop, and the tankless starves at full fire. Check its rating on the valve tag against the new load.
What the shop actually does. Before quoting, it sends the new connected load to the utility's load-change or new-service desk. The utility checks the meter, regulator, service line and excess flow valve against 366 cubic feet per hour and tells the shop what it will change and when. The house piping is sized separately, by the fuel gas code's tables as adopted, for the new load and the developed length. The install date goes after the utility's work, not before.
What changes the answer. A house on an old service line with no excess flow valve has nothing at the main to trip, but the meter and regulator still have capacities and the utility still has to approve a load increase. A house served at elevated pressure with a regulator at the meter may have line capacity to spare and an excess flow valve sized generously. The fact that decides it in every case is the utility's record, which the shop does not have and should not guess.
Questions customers ask, and straight answers
"Do I have one of those valves the utility is supposed to put in?" If your service line was installed or replaced since the federal requirement took effect around 2010, very likely; the utility can tell you, and under the federal rule it has to offer one on request for most existing residential lines.
"Should I install a seismic valve?" In a jurisdiction that requires one, the decision is made. Elsewhere it is a reasonable choice in a high-shaking area, with two costs worth stating plainly: a bump can trip it, and after any trip every pilot in the house has to be relit, which in a winter quake with the whole region calling means a cold house until someone gets there.
"Can you reset it?" A tripped seismic valve, yes, after finding out why it tripped and checking the piping. A utility valve, no.
How to verify you read the house right
- The ticket says which device tripped and how you knew: every appliance out with a seismic valve showing tripped, or loss of supply at the meter inlet.
- No reset happened before the leak check, and the leak check is recorded.
- Any load increase went to the utility with the before and after totals in cubic feet per hour, and the utility's answer is in the job file.
References
- 49 CFR 192.383, excess flow valve installation on service lines, as amended in 2017
- ASCE/SEI 25, Earthquake-Actuated Automatic Gas Shutoff Devices, where adopted by local ordinance, and the California Division of the State Architect's valve certification program
- The fuel gas code your jurisdiction has adopted, for house piping sizing on a load change
- See related: How to Strap a Water Heater for Earthquakes; Anchoring Equipment and Ducts in Seismic Regions; How to Check a House for Earthquake Readiness on a Service Call