How to Tell If You Have a Gas Leak
Knowing how to tell if you have a gas leak can protect your family from fire, explosion, and carbon monoxide poisoning. Natural gas is odorless on its own, but utilities add a chemical called mercaptan that smells like rotten eggs so leaks are easier to notice. Still, not every leak announces itself with a strong smell, and some leaks happen outdoors or in places you rarely visit. This guide covers every warning sign, what to do the moment you suspect a leak, and how a professional finds and fixes the problem.
The Rotten Egg Smell
The sulfur-like, rotten egg odor is the sign most people recognize first. Gas companies add mercaptan to natural gas precisely because it is so hard to ignore. If you notice this smell near a stove, furnace, water heater, fireplace, or gas meter, treat it as a possible leak until proven otherwise. The smell may be faint if the leak is small or if it is outdoors where wind disperses the gas. It may also be stronger in one room than another, which can help you narrow down the source, but do not go hunting for it with your nose pressed to pipes and fittings.
There are a few reasons the smell can be misleading. A dry drain trap can produce a sewer-gas odor that smells similar. A dead animal in a wall or a plumbing problem can also mimic it. Even so, never assume a rotten egg smell is harmless. If the smell is new, persistent, or seems to come from a gas appliance or line, leave the area and call for help. A gas utility will typically come out free of charge to check for a leak, and that free check is always worth it. If you want to understand what a professional inspection involves, see our guide to gas line inspection cost and what is included.
Hissing or Blowing Sounds
A damaged or disconnected gas line can release gas under pressure, producing a distinct hissing, whistling, or roaring sound. You might hear it near a gas meter, at a shutoff valve, behind a stove, or around a furnace connection. Outdoors, a leak in a buried line can blow dust or dirt into the air or create a visible cloud of dust above the ground. In wet weather, you may see bubbles in a puddle or standing water over a buried line.
Sound alone is not a reliable test. Small leaks often make no noise at all, and background noise from appliances can mask a hiss. If you do hear an unexplained hissing sound near any gas equipment, do not try to tighten a fitting or shut off the gas yourself unless you already know exactly where the shutoff valve is and can reach it safely without using any electrical switches. The safest move is to get everyone out of the house and call from outside. For more on the rules around gas work, read who can legally install a gas line.
Dead Grass and Dying Plants
An outdoor gas leak can kill grass, shrubs, and other plants in a defined patch or strip above the buried line, even when the rest of the lawn is green and healthy. Natural gas displaces oxygen in the soil, starving roots. If you notice a patch of dead or yellowing grass that does not respond to watering, or a line of dead vegetation running from the street toward your gas meter, a buried line leak is a real possibility. You may also see a white mist or fog hovering over the ground on a cool morning, or dust blowing from a small hole in dry soil.
Outdoor leaks are easy to overlook because the gas disperses into the air and the smell fades quickly. If you see unexplained dead vegetation near a known gas line route, call your gas utility and report it. In the United States, you can also call 811 before any digging project so underground lines are marked for free. Never dig to investigate a suspected buried leak yourself. Striking a gas line with a shovel or digging equipment can turn a slow leak into a dangerous one in seconds.
Physical Symptoms to Watch For
Exposure to leaking natural gas can cause headaches, dizziness, nausea, fatigue, eye and throat irritation, and difficulty breathing. In an enclosed space, gas displaces oxygen, and carbon monoxide from a malfunctioning gas appliance can cause confusion, chest pain, and loss of consciousness. These symptoms are especially dangerous because they can come on gradually, and people often blame them on a cold, allergies, or poor sleep.
One useful clue is whether symptoms improve when you leave the house and return when you come back. If several people in the household feel ill at the same time, or if a pet that stays indoors becomes lethargic or vomits, take it seriously. Move everyone, including pets, outside into fresh air and call emergency services. If anyone is unconscious, has trouble breathing, or shows signs of carbon monoxide poisoning, call 911 right away. Do not re-enter the house to grab belongings or to open windows. Fresh air and distance are the priorities.
Higher-Than-Normal Gas Bills
A sudden, unexplained increase in your natural gas bill can be a quiet sign of a leak. Compare your current bill with the same month last year and with recent months. If usage has jumped while your habits and the weather have not changed much, gas may be escaping somewhere in the system. A running gas appliance, such as a water heater cycling more than usual, can also be a clue. Keep in mind that rate increases and colder weather also raise bills, so a higher bill alone does not prove a leak, but combined with any other sign on this list it is worth reporting.
Many utilities offer free leak checks and will investigate a usage spike if you call them. When you call, mention the bill change and any other symptoms you have noticed. The technician can test the meter and lines with a combustible gas detector, which is far more sensitive than your nose. If a leak is found on the utility side of the meter, the utility usually repairs it. If it is on your side of the meter, you will need a licensed plumber or gas fitter, and you may want to review gas line permit requirements before any repair work begins.
What to Do Immediately
If you suspect a gas leak, act fast and keep it simple. First, leave the house right away. Get every person and pet out, and do not stop to collect valuables. Second, once you are safely outside and away from the building, call 911 and then your gas utility emergency line. Tell them you smell gas or suspect a leak, and give your address. Third, stay outside and away from the house until emergency responders or the utility say it is safe to return. Do not go back inside for any reason while the leak is unresolved.
If the leak is outdoors and you can smell gas near the meter, move upwind and keep neighbors away from the area. If you know where your gas meter shutoff valve is and you can reach it safely from outside without entering the building, some utilities advise turning it off, but only if you are certain you can do so safely. Never turn the gas back on yourself. Only the utility or a qualified professional should restore service after a leak, because lines must be pressure-tested first. For a comparison of common gas piping materials used in repairs, see CSST vs black iron gas pipe.
What NOT to Do
When gas is leaking, a single spark can ignite it. Do not flip light switches, garage door openers, or any electrical switches on or off, because switches can spark. Do not use a landline phone or cell phone inside the house, and do not unplug appliances. Do not light matches, candles, or cigarettes, and do not start a car parked in an attached garage. Do not use a flashlight inside the affected area unless it is rated for hazardous locations, since standard flashlights can spark when switched on.
Do not try to find the leak with a flame, a lighter, or a soapy-water test on your own. Do not attempt to repair a gas line yourself unless you are qualified and licensed for gas work in your area. Gas work done incorrectly can create a much larger hazard than the original leak. Also, do not open windows and doors to ventilate and then stay inside, thinking the problem is handled. Ventilation does not make a leaking home safe, and the gas will keep flowing. Leave, call, and wait for professionals.
Getting the Leak Fixed
Once the utility confirms a leak, the next step depends on where it is. Leaks on the street side of the meter are generally the utility's responsibility. Leaks on your side, including appliance connectors, interior piping, and the line to an outdoor grill or pool heater, are the homeowner's responsibility and must be repaired by a licensed professional. The technician will locate the leak with a gas detector or pressure test, isolate the damaged section, and replace or repair it. After the repair, the system is pressure-tested again before gas service is restored.
Costs vary with the location and extent of the damage. A simple appliance connector replacement may cost a few hundred dollars, while replacing a long run of buried or concealed piping can cost several thousand. Most homeowners also use the opportunity to have the whole system inspected, since one leak can signal aging pipe or corroded fittings elsewhere. If your home still has old piping, ask the technician about the condition of the rest of the system and whether an upgrade makes sense. Keep records of the repair, including the permit and inspection sign-off, since buyers and insurers may ask for them later. For more background, browse our gas lines hub for guides on inspections, materials, permits, and safe installation.
If you suspect a gas leak right now, do not wait to finish reading. Leave the house, and from outside call 911 and your gas utility. For non-emergency questions about inspections or repairs, call (877) 762-1902.