Gas Smell in the House? Here's Exactly What to Do First
You walk into the kitchen in the morning to make coffee and stop. That rotten-egg smell hits you — faint, somewhere between a skunk and something burnt. You check under the sink. Nothing obvious. You wonder if maybe you're imagining it.
You're not imagining it. That smell means something. The question is whether it means leave the house right now and call 911, or whether it means your basement floor drain has gone dry. Those are not the same situation, and treating them the same wastes time in one case and keeps you in a house you should have left in the other.
Here's what the different smells actually tell you and what to do about each one.
Quick Reference: Gas Smell Sources at a Glance
| What you smell | Where it concentrates | Most likely source | Action |
|---|---|---|---|
| Strong rotten eggs | Throughout house, near appliances | Natural gas leak — call 911, leave now | Evacuate, don't touch switches |
| Faint rotten eggs, clears quickly | Near stove after lighting | Normal pilot lighting | Monitor; call if it doesn't clear |
| Rotten eggs near floor drains or basement | Basement, laundry area | Dry P-trap or sewer gas | Run water down drains; call a plumber |
| Rotten eggs from hot water tap only | Kitchen or bathroom sink | Anode rod reaction in water heater | Call a plumber |
| Rotten eggs with gurgling drains | Anywhere in the house | Sewer line problem | Call a plumber |
| Rotten eggs after fall furnace startup | Near furnace or vents | Dust/residue burning off or heat exchanger | Run for 20 minutes; if it persists, call |
What you're actually smelling
Natural gas has no odor on its own. Neither does propane. Gas companies add a chemical called mercaptan — sometimes called an odorant — specifically so you can detect a leak. It smells like rotten eggs, skunk spray, or sulfur. The concentration is small: just enough for a human nose to catch it even at low leak levels.
When that smell hits your house, your nose is doing exactly what it was designed to do in this system.
But here's what that system can't do: tell you whether the rotten-egg smell is coming from the gas line or from somewhere completely different. Hydrogen sulfide — the compound behind that odor — gets produced naturally by bacteria in drains, sewer systems, and water heaters. It smells almost identical to mercaptan. This matters because the correct response to a dry P-trap is not evacuating your house and calling 911.
Where the smell is coming from makes all the difference
Near the stove, range, or oven. A faint gas smell that appears when you turn a burner to light it and clears within a few seconds is normal. Gas flows through the burner for a brief moment before igniting. But if the smell lingers after the flame is lit, or if you smell gas when no burner is on, that's not normal and needs attention.
Near the furnace. The first time you fire the furnace up in fall after months of sitting idle, dust and residue burn off the heat exchanger and burners. You might smell something odd for 10 to 20 minutes. If it clears, that's typical. If you're getting a rotten-egg smell around the furnace that won't clear, or you hear a hissing near the gas line feeding the unit — stop the furnace and call. A cracked heat exchanger can push combustion gases into the airflow throughout your house. That's the kind of problem that doesn't show symptoms until someone is sick.
Near floor drains or in the basement. Floor drains in basements and laundry rooms have P-traps — curved pipe sections that hold a small plug of water as a vapor seal. When a drain goes unused for two to four weeks, that water evaporates. Without the seal, sewer gases rise up through the opening into the room. This is extremely common in basements where the floor drain never gets any water. The fix is as simple as running a gallon of water down the drain. If the smell comes back within a couple of days, you've got a venting problem, not just a dry trap.
From the hot water tap only. If the rotten-egg smell comes specifically from hot water and not cold, the source is almost certainly the anode rod in the water heater reacting with bacteria in the water. High sulfur content — common in areas with private wells or older municipal supplies — accelerates this reaction. This is a plumbing problem. Not a gas emergency.
Everywhere in the house at once. A smell that's present throughout multiple rooms, that doesn't seem to be coming from any one appliance, that's getting stronger rather than fading — treat it as a gas leak.
What natural gas does vs. what propane does
Most homes in eastern Pennsylvania run on natural gas from a utility. Some rural properties use propane from a tank. They behave differently in one important way: natural gas is lighter than air, so it rises. Propane is heavier than air — it sinks.
A natural gas leak accumulates near the ceiling first. An open window can help vent it out. Propane from a leaking line or appliance drops to the floor. It collects in basements, crawl spaces, and low spots — pooling there without the smell ever reaching the main living areas. This is why propane leaks can be harder to notice until the concentration is already significant.
If your home runs on propane, the floor-level spaces are where a leak would concentrate: the basement, under kitchen cabinets, and any sunken room. That's also where your detector should be mounted — within 18 inches of the floor, not up near the ceiling where you'd put a natural gas detector.
What to do if you think you have a gas leak
This is the sequence that matters. Each step has a reason.
Leave the house. Don't stop to turn things off. Don't grab belongings. Get everyone out, including pets.
Don't touch any electrical switches. Light switches, thermostats, doorbells, and phone chargers all create a small arc when they toggle. That arc is enough to ignite the gas that's collected in the room.
Don't use your phone inside the house. Step well outside — 300 feet or more — before calling anyone.
Don't open or close the garage door. The opener is an electrical device and will spark.
Leave the front door open on your way out. It helps ventilate, and you're already moving.
Once you are outside: call the gas utility's emergency line, then 911. Utility companies have a 24/7 emergency response and bring equipment to test the gas concentration before anyone goes back inside. Don't go back in. Don't try to find the leak yourself.
And don't turn the gas back on yourself once the utility clears the scene. Someone with the right equipment should relight pilot lights and verify all appliances are running correctly after any suspected leak.
What happens after you call the gas company
The utility sends a technician with a combustible-gas detector — an electronic instrument that reads gas concentration in the air. They test every room and around every appliance. If they find a leak at the meter, the service line, or the main shutoff, they'll cut the gas at the street and tag the line.
If the leak is inside the house, in your own piping, they hand off to a licensed plumber. The utility is responsible for lines up to and including the meter. Everything from the meter into the house is the homeowner's side of the line.
A plumber will pressure-test the interior gas system to locate the source, then repair or replace the affected section. Gas piping work requires a license. Any repairs to the gas system should be permitted and inspected before the gas is turned back on.
Why older homes deserve extra attention
A lot of homes in eastern Pennsylvania were built before 1980 — many in the 1940s through 1960s. The gas piping in those homes is typically black iron pipe with threaded fittings at every joint.
Black iron pipe itself holds up reasonably well. The fittings are the weak point. Thread compound dries out over decades. Fittings that have been vibrated by nearby construction, freeze-thaw movement, or just normal settling can develop hairline leaks. Homes that have had appliance upgrades over the years — a new furnace, a new water heater, an added gas dryer — may have a mix of old iron pipe and newer flexible corrugated stainless steel tubing (CSST) connected without proper bonding.
Think of an old gas fitting like a jar lid that's been opened and resealed dozens of times. Each time, the seal gets a little less reliable. It doesn't fail dramatically — it just allows a small amount of gas to escape, often not enough to smell under normal ventilation, but enough to build up in a closed basement or a room that rarely gets opened.
If your home is more than 40 years old and you haven't had the interior gas system inspected, that's worth doing before you ever smell anything.
How to reduce the chances of this happening
Annual inspection of every gas appliance — furnace, water heater, stove, dryer — catches deteriorating burners, cracked heat exchangers, and worn connectors before they become leaks. A plumber or HVAC technician can also inspect the visible gas supply lines while they're servicing equipment.
Install a gas detector. A natural gas or propane detector (depending on what your home uses) plugs into a wall outlet and alarms before the gas reaches a dangerous concentration. These run $30 to $80. They are separate from carbon monoxide detectors — you need both.
Keep infrequently used floor drains wet. Pour a gallon of water down any basement or laundry drain once a month. Thirty seconds of work keeps the vapor seal intact and prevents the sewer-gas-vs.-gas-leak confusion entirely.
Have the gas system pressure-tested if you are buying an older home, adding a gas appliance, or haven't had any inspection in more than five years. A pressure test applies air to the gas line and checks for pressure drop — the definitive way to confirm whether any section of pipe is losing gas.
Frequently Asked Questions
Not always, but always worth attention. A smell that appears briefly when a gas appliance lights and then clears is normal. A smell that lingers, comes back repeatedly, or gets stronger is not. When you can't explain where it's coming from or it won't clear with ventilation, leave the house and call.
Yes, depending on concentration. Hydrogen sulfide from sewer gas is toxic in high amounts. The concentrations from a dry P-trap usually aren't dangerous, but prolonged exposure in a poorly ventilated space can cause headaches and nausea. If you're smelling it regularly, find the source.
If your homes are from the same era and use similar piping, a failure next door is a good reason to have your own system checked. Aging infrastructure across similar conditions tends to fail within similar windows.
The utility or fire department will tell you when it's safe. They test the gas concentration on instruments and clear the scene when it drops below threshold. Don't estimate this yourself based on how much time has passed.
Barometric pressure changes during storms affect how gases move through the plumbing vent pipes on your roof. Low pressure can push sewer gas down into the house through any gaps in the system. If rain consistently brings a rotten-egg smell, the vent stack is worth inspecting for blockages or damage — leaves, bird nests, and broken caps are common culprits.
Work on interior gas piping is permitted work. A licensed master plumber or gas contractor pulls the permit, completes the repair, and the work gets inspected before the gas is turned back on. This isn't optional — it's how you confirm the repair was done correctly.
Gas smells don't always mean an emergency, but they always mean something. The fastest way to figure out which situation you're dealing with is knowing where the smell is coming from and whether it's growing or fading. A rotten-egg smell that won't clear after 10 minutes of ventilation, that appears throughout the house, or that you simply can't place, deserves a call — to the gas utility first, then to a plumber for whatever they find inside the house.
