You Smell Gas. Here's Exactly What to Do — and What Not to Do.
- Lamont Plumbing & Heating
- Mar 3
- 6 min read
Updated: Mar 3
Let's start with the thing that matters most: if you smell gas strongly and suddenly — stop reading this, get everyone out of the house, and call 911 and your gas utility from outside. That's it. Don't look anything up. Don't grab belongings. Don't flip a light switch. Just get out.
If you're reading this because something smelled a little off and you're not sure what it was, or you want to know what to do before it ever happens — this post is for you. We've worked with gas lines for our entire careers as licensed Massachusetts gasfitters, and we want you to know exactly what we'd tell our own families.
🥚 Why Gas Smells Like Rotten Eggs — and Why That's Intentional
Here's something most people don't know: natural gas and propane are both completely odorless in their natural state. You cannot smell them at all. The rotten egg or sulfur odor you associate with a gas leak is a chemical called mercaptan, which gas utilities add deliberately so that leaks can be detected by smell alone.
It takes only a tiny amount of mercaptan to produce a very noticeable odor — which means if you can smell it at all, there is enough gas present to warrant your full attention. The smell is not subtle by design. If you're catching a whiff of rotten eggs anywhere near a gas appliance, a gas line, or for no apparent reason at all — that is not something to dismiss.
💡 Good to Know
Some people have a reduced ability to detect mercaptan — particularly older adults. If you live with someone whose sense of smell isn't sharp, a natural gas detector installed near your appliances is an inexpensive and genuinely important safety device. We recommend one near the water heater, furnace, and kitchen range.
🚨 Strong Gas Smell — Do This Right Now
A strong, sudden smell of gas is an emergency. Treat it like one. Here is the exact sequence — memorize it or share this post with everyone in your household.
🚨 Emergency Protocol — Strong Gas Smell
Follow these steps in order. Do not skip any.
1.Don't touch any switches.Do not turn lights on or off. Do not unplug anything. Even a small electrical spark can ignite gas. Leave everything exactly as it is.
2.Don't use your phone inside.Get outside first, then call. A ringing phone has ignited gas before.
3.Leave the door open as you go.This helps ventilate — don't slam it, just leave it open.
4.Get everyone out — people and pets.Don't go back for anything.
5.Once outside, call 911and then your gas utility — National Grid: 1-800-233-5325 or Eversource: 1-800-592-2000.
6.Wait outsideand away from the building. Do not re-enter until emergency responders clear it.
🚫 What NOT to Do — Ever
Do not turn light switches on or off
Do not light a candle, match, or lighter anywhere in or near the house
Do not use your cell phone, garage door opener, or any electronic device inside
Do not turn the stove on to "burn off" the gas — this is a myth and it is dangerous
Do not open windows to air it out and then stay inside to wait
Do not assume the smell will go away on its own
Do not re-enter the building until a professional has cleared it
👃 Faint Smell — What Does That Mean?
A faint, intermittent smell of gas is a different situation — it warrants real attention, but it isn't necessarily the same emergency as a strong sudden smell. It could be a pilot light that went out, a burner that didn't ignite fully, a loose fitting on a connection, or a small leak that has been slowly developing.
The right response to a faint gas smell: ventilate the space by opening windows, turn off any nearby gas appliances at their control knobs — do not use the electrical switches — and call your gas utility or a licensed gasfitter to inspect. Do not try to find the leak yourself.
⚠️ One Important Distinction
A faint smell near a gas range right after you've tried to light a burner and it didn't catch is usually just unburned gas dissipating — open a window and try again after a minute. A faint smell with no obvious source, or a smell that keeps coming back, is a different story entirely. That one needs a professional.
💨 Carbon Monoxide — The Leak You Can't Smell At All
While we're talking about gas safety, we'd be doing you a disservice not to address carbon monoxide — because it's the thing that actually kills people, and it has no smell whatsoever.
Carbon monoxide is produced by incomplete combustion — any gas appliance that isn't burning cleanly can produce it. A cracked heat exchanger in a furnace. A blocked flue. A gas water heater in a poorly ventilated space. A malfunctioning boiler. You cannot detect it without a detector. It causes headaches, dizziness, nausea, and confusion — symptoms that are easy to attribute to a cold or flu — before it becomes life-threatening.
400+ Americans die from CO poisoning annually — most in their own homes
100K+ ER visits each year from unintentional CO exposure
#1Cause of fatal poisoning in the US — most cases are preventable
🚨 If Your CO Detector Sounds
Treat it identically to a gas leak — get out immediately.
✅ Detectors Every Home Should Have
Carbon monoxide detectors on every level of the home and outside every sleeping area — Massachusetts law requires them. Natural gas detectors near your appliances — not required by law but genuinely recommended. Both should be tested monthly and replaced every 5–7 years. The combination CO/gas detector units are a cost-effective option.
🔴 The Red Tag — What It Means and Why You Can't Ignore It
If a gas utility technician — from National Grid or Eversource — has visited your home and placed a red tag on one of your gas appliances or your gas meter, that appliance has been shut off and condemned as unsafe to operate. The gas has been turned off to that unit specifically, or in some cases to the whole house.
A red tag is not a suggestion. It is a safety order. The utility has the legal authority to shut off your gas and will not restore it until a licensed gasfitter has repaired the problem, signed off on the work, and the utility has re-inspected. Removing a red tag yourself and restoring the gas is illegal and genuinely dangerous.
What a Red Tag Means
A safety violation has been found
The appliance or line is unsafe to operate
Gas has been shut off to that unit
A licensed gasfitter must make repairs
Utility re-inspection required to restore
Common Red Tag Causes
Improper venting on an appliance
Corroded or deteriorating gas line
Unlicensed gas work discovered
Failed pressure test on a line
Appliance too close to combustibles
If you've received a red tag, call us. We handle red tag corrections regularly — we'll assess what needs to be done, pull the proper permits, make the repairs, and coordinate with the utility to restore your gas service as quickly as possible.
🔍 Proactive Gas Safety — What a Smart Homeowner Does
The best gas emergency is the one that never happens. Here's what we'd suggest for any MetroWest homeowner with gas appliances:
💡 Proactive Gas Safety Checklist
Install detectors — CO detectors on every level, gas detector near appliances. Test monthly.Know your shutoffs — know where the gas shutoff is at your meter and how to use it. Every adult in the house should know this.Never ignore a smell — even a faint, occasional smell of rotten eggs near gas appliances. Call it in.Schedule annual appliance maintenance — your furnace, boiler, and water heater should all be inspected and serviced annually by a licensed professional. A clean, well-maintained appliance is a safe one.Don't do your own gas work — in Massachusetts, all gas work must be performed by a licensed gasfitter, permitted through your town, and inspected. There are no exceptions. Unlicensed gas work voids your homeowner's insurance and is genuinely dangerous.
Gas is a safe, efficient fuel source when it's properly installed and properly maintained. In twenty years of licensed gas work in MetroWest, we've seen very few emergencies in homes where the systems were properly installed and regularly serviced. The emergencies we see are almost always in homes where something was ignored, something was done without a permit, or something was deferred for too long.
Take the five minutes to test your detectors. Know your shutoffs. And if something smells wrong — trust your nose.
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Licensed Massachusetts Gasfitter · Holliston, MA · Serving MetroWest Boston