It’s concerning if you smell gas near your furnace. Natural gas smells like rotten eggs (thanks to an additive in the gas), which is an indication that there is a leak in your furnace or its gas source. While it’s okay to smell a tiny bit of gas near your furnace during its ignition sequence (if you have an electronic ignition), you shouldn’t smell gas when your furnace is off, or if it has been running for a minute. If you smell gas, then you may have a dangerous leak, and you should act right away to close off the source of the leak. Here’s what you should do if you smell gas leaking from your furnace:

1. Turn off your furnace at the thermostat — there should be an “off” setting.
2. Open nearby windows to dissipate any gas that has built up. Leave these windows open for several minutes to ensure that the space is safe.
3. Turn off the gas valve to your furnace. You should be able to locate the gas line that approaches your furnace, and the gas valve switch. Turn the switch off.
4. If your gas valve is malfunctioning, shut off the gas main for your home.
5. Contact an HVAC technician to take a look at your furnace and to assess the source of the leak.

Take note, you should not breathe in natural gas, since it is dangerous to your health. In addition, if you note that the gas levels are high and you think it is unsafe to turn off the gas yourself, you should vacate your home and contact emergency services to report a gas leak.