Smell Gas Near Your Furnace? What to Do First

Natural gas is odorless until a utility adds a smell to it, and that smell is your warning. When it reaches your nose near a furnace, the safe response is the same every time: get out, then call. Everything about the furnace itself comes after that.

What should you do the moment you smell gas?

Leave first and make every call from outside. Spire's page lists 800-887-4173 as its Eastern Missouri number for reporting gas leaks and other gas emergencies at any hour, and says to leave the area immediately before calling Spire or 911.

1. Walk out of the building now. Take people and pets, but do not search for belongings.
2. Do not flip light switches, use the garage door opener, light a match or start a car in an attached garage.
3. Use a phone from outside, preferably away from the house, to call 911 or Spire at 800-887-4173.
4. Stay outside until responders say the building is safe.
5. Do not return to relight, test or repair anything.

After you are safe and the utility has cleared the building, you can call a specialist about the furnace.

Should you shut off the gas before you leave?

No. Spire says only the utility should turn gas service back on once it has been shut off, and every second spent hunting for a valve is a second spent inside. The trade-off is real: a faint smell near a furnace shutoff tempts people to reach for it. Resist, because a valve handle is a surface that has to be touched near the leak, and the crew has tools to shut the service off safely.

What about neighbors and shared buildings?

Warn people by knocking with your hand, not by ringing a doorbell, because PHMSA notes a doorbell or metal knocker can spark. In an apartment or duplex, tell the other units on your way out and let the utility's call cover the whole building. Tell the landlord or manager after you are safe. If you use propane, call your propane supplier's emergency line and 911, and know that propane odor can fade, so a detector matters more.

What does a gas leak smell like, and what else should worry you?

Utilities add a chemical called mercaptan to natural gas so people can notice a leak. A September 2025 report from First Alert 4 notes that Spire described the rotten-egg smell as mercaptan, a harmless odorant added for safety. The odor is the signal, not a cause of harm.

Other signs call for the same caution:

• A hissing or whistling sound near a gas line or appliance
• A burner flame that burns yellow or orange instead of steady blue, which signals poor combustion and needs a technician
• A carbon monoxide alarm that sounds, which is a separate emergency handled the same way

Is every furnace smell a gas leak?

No, and the table below helps you sort them. When you are unsure, treat it as gas and leave.

Why can the smell be misleading?

Your nose gives you a yes or a maybe, never a no. Spire warns that escaping gas can migrate underground and through structures and collect far from the source. Natural gas also tends to collect at the highest point of a space, so a smell near a basement ceiling or an upstairs closet does not prove the leak is there. PHMSA's advice is to leave on foot and not try to locate the source. The practical rule is that any odor you cannot explain is reported, whether or not it fades.

Why would gas leak near a furnace?

Leaks near a furnace come from a short list of places. Gas valves, flexible connectors, threaded fittings and old pilot assemblies are the usual suspects. Appliances reconnected after a move or a remodel can be left with a loose union. Corrosion on old iron pipe in a damp basement can also open a pinhole.

A cracked heat exchanger is not a gas leak, but it can send carbon monoxide into the house, which is why a technician should check the furnace before it runs again after any shutdown. Our emergency furnace repair page explains the visit, and the furnace repair page covers ignition and valve faults. Homes with hot-water boilers have their own gas train; see boiler service.

How is a leak actually found and fixed?

A technician typically checks suspect fittings with a combustible gas detector and a bubble solution, then isolates sections of piping and watches a gauge to see whether pressure holds. A gauge that drifts down means a leak somewhere in that section. Our guide to passing a gas inspection covers what an inspector looks for.

The repair choices carry trade-offs. A worn flexible connector or a loose union is a low-cost fix. A leaking gas valve or a corroded section of old iron pipe costs more, and on a furnace near the end of its commonly quoted 15-to-20-year life, a failed gas valve can tip the repair-or-replace question. Ask which fitting leaked, what was replaced, and what the pressure test showed.

How do you prepare before a gas smell ever happens?

Ten minutes now saves confusion at 2 am. Use this checklist.

• Save 800-887-4173 in every adult's phone and post it near the door.
• Pick a meeting spot at the curb or a neighbor's walk and agree who makes the call.
• Walk the exit routes from bedrooms and the basement, and teach children not to touch switches.
• Check that a CO alarm sits near each sleeping area and test it monthly.
• Learn where the meter and appliance shutoffs are, for information only.
• Keep furnace and boiler service current, so valves and connectors get a look each year.

From the field: gas problems found and fixed

Two Google reviews describe gas work from the customer's side. Frederick E. wrote that after a gas inspection, the technician found the leaks, fixed them, tested the pressure and passed Spire's reinspection when the utility returned. A Google reviewer whose gas had been shut off for a leak wrote that Kenan Corporation arrived on the day of the call at the time promised and talked them through the process.

What to take from both: have the piping pressure-tested after a repair and ask what was found. We cannot promise an arrival time for your call, and these are individual stories, not guarantees.

What happens after the utility clears the home?

After the utility clears the home, a repair visit starts with the piping. The technician locates the leak, explains it in plain language, and gives a clear, upfront quote before work starts. After the repair, a pressure test shows whether the lines hold, and the utility may need to reinspect before service is fully restored.

If the leak was at an appliance, ask whether other gas appliances were checked. Once the home is cleared, Kenan Corporation can be reached at any hour, with same-day visits when the schedule allows. Keep any paperwork from Spire or a home inspection and give it to the technician. Ask for every gas appliance to be checked, including the water heater, range and dryer, not just the furnace. In Richmond Heights, the drive from our base near Spanish Lake is about 35 minutes in normal traffic, and Maplewood is about 40 minutes.