Furnace Gas Leak: Warning Signs and Emergency Steps
Suspect a furnace gas leak? Leave the building immediately. From a safe location away from the suspected leak, call 911 in the United States and your gas utility’s emergency number. Do not stay near the furnace to troubleshoot it.
Accuracy review: September 15, 2026. This guide addresses suspected fuel-gas leaks and carbon monoxide concerns.
What to do if you smell gas near the furnace
- Get everyone out. Move away from the building and the suspected leak.
- Avoid ignition sources. Do not operate light switches, the thermostat, breakers, plugs, phones or vehicles in the affected area. Do not smoke or use flames.
- Call from a safe location. Contact emergency services and your gas utility. Tell them where you noticed the odor or sound and whether anyone feels unwell.
- Wait for responders. Do not go back inside to investigate or collect belongings. Follow their instructions about re-entry and restoring service.
These steps follow PG&E’s gas emergency guidance and PHMSA’s leak-response guidance. Outside the United States, use your local emergency number and gas supplier.
Warning signs do not require a DIY confirmation test
A sulfur or rotten-egg odor, or an unusual hissing sound around gas equipment, can signal a leak. An absent odor does not establish that an area is safe. Do not search for the source with a flame, perform a bubble test during a suspected emergency, tighten fittings, relight burners or operate the gas meter yourself. Leave assessment and repairs to the gas utility and qualified professionals.
PHMSA advises against operating pipeline valves or attempting to extinguish a natural-gas fire. Report what you noticed from safety; do not return to obtain better photos or a model number.
Natural gas, carbon monoxide and water leaks are different
| Concern | What matters |
|---|---|
| Fuel-gas leak | Escaping fuel can create a fire or explosion hazard. Treat a suspected leak as an emergency. |
| Carbon monoxide (CO) | CO is an odorless, colorless poisonous gas associated with fuel burning. Smell cannot detect it. |
| Water around the furnace | A puddle alone does not establish a fuel-gas leak or a cracked heat exchanger. Water requires a separate diagnosis. |
If a CO alarm sounds, leave immediately and call 911 from outside. Headache, dizziness, weakness, nausea, vomiting, chest pain or confusion can be symptoms of CO poisoning. Get to fresh air and obtain immediate medical help if exposure is suspected. Do not delay leaving while trying to identify the appliance. See CDC’s CO guidance and CPSC’s CO alarm guidance.
After the emergency has been made safe
Ask the responding utility or emergency service who must complete the repair and what must happen before gas service or the furnace can be used again. Do not assume the furnace is safe because the odor has faded.
Keep the incident or service reference number, the responder’s instructions and any written repair findings. For subsequent HVAC work, request an explanation of the confirmed fault, the proposed repair and the checks needed before the equipment returns to service. A symptom alone is not a reason to order a replacement gas valve.
Preventive checks when there is no emergency
Have fuel-burning heating equipment serviced by a qualified technician each year. Maintain CO alarms according to their instructions and replace them at the specified end of life. Alarms complement maintenance; they do not replace it. CDC explains prevention and annual servicing.
If responders have ruled out a gas or CO emergency and your actual problem is water, use the separate furnace leaking water guide. For a non-emergency ignition failure, see furnace won’t ignite: owner checks.
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