Your furnace comes on and you suddenly notice a strange odor, but you aren’t sure what it could be. This scenario happens more often than you might think, and sometimes it’s not a cause for concern. There are also times when a strange odor can be a sign of a serious problem that could result in an electrical fire or exposure to deadly carbon monoxide. That’s why it’s essential to understand what different furnace odors can mean and when they may indicate an emergency.
Burning Smell
You’ll usually notice a burning smell when you first turn your furnace on in the fall. Furnaces can collect quite a bit of dust when they sit unused over the summer. Once you turn the furnace on, the dust quickly starts burning off and producing a noticeable odor that spreads around the house through the air ducts. The smell usually goes away within 30 minutes or so, but it could linger for a few hours. If the odor gets stronger or doesn’t go away, shut off the furnace at the thermostat and schedule furnace repair services. It’s also essential to immediately shut off your furnace if you notice a burning smell any time other than when first turning your heating on.
A burning smell can be a sign that the furnace or blower motor is overheating. While there’s a safety switch that’s designed to cause an immediate shutdown if overheating occurs, the switch could be faulty or not trip as it should. An overheating blower motor may also start to smoke. Another possibility is that there’s a damaged or frayed wire. Electrical issues can lead to wiring melting, creating the potential for a dangerous electrical fire.
Rotten Smell
You should be seriously concerned if you notice a smell similar to rotten eggs or sulfur. This type of smell is usually a sign of a gas leak, which can lead to a major fire or even a massive explosion. If the smell is only faint, close the valve on the furnace’s gas line and then immediately get everyone and your pets outside. If the smell is strong, don’t worry about closing the gas valve and just leave immediately. Once you’re outside and a safe distance away from your house, call 911 and report the gas leak.
Metallic or Chemical Smell
A metallic or chemical smell can also be a sign of overheating or electrical issues that could lead to a fire. If you notice a chemical odor similar to formaldehyde, it usually indicates that there’s a crack in your furnace’s heat exchanger. Not only is a cracked heat exchanger extremely dangerous, but it also means that you’ll need an immediate heating replacement.
The heat exchanger is sealed to ensure that the combustion fumes get vented outside. If there’s a crack in it, the combustion fumes can leak out and mix with the hot air inside the furnace. This is a serious concern, as it can expose everyone to carbon monoxide. While carbon monoxide itself is odorless, the formaldehyde smell is a sure sign that combustion fumes are leaking out.
Annual heating maintenance and safety inspections are crucial for avoiding and detecting issues like a cracked heat exchanger. Maintenance also helps reduce the risk of overheating and other issues that can lead to unusual smells and safety hazards.
Musty Smell
Musty smells are less of a concern, but they can indicate issues that negatively impact your indoor air quality or potentially damage your furnace. One possibility is that the furnace filter is clogged and needs to be replaced. Musty odors can also be a sign of dirty ductwork.
If you have a high-efficiency condensing furnace and you notice a mold or mildew smell, water is likely leaking out of the condensate drain system. This usually happens because of a clog in the drain line. It’s also possible that the drain pan is leaking or that one of the pipes has come loose. This type of issue is something you need a professional to fix as soon as possible due to the risk of components rusting. The biggest concern is if the heat exchanger rusts, as rust can lead to a crack or hole.
What to Do Next
There are a few things you can do to potentially troubleshoot certain unusual smells. The following checklist will explain what steps you can take.
- Turn the furnace off and replace the air filter.
- Check for signs of water around the furnace.
- Wait around 30 minutes and then turn the furnace back on to see if the smell returns.
- If the smell returns, turn the furnace back off and call for an inspection.
For over 90 years, National Heating & Air Conditioning has been providing trusted HVAC services to Cincinnati homeowners and businesses.
We offer 24/7 emergency heating services and are ready to expertly handle your concerns. To schedule a furnace inspection or maintenance service, contact us today.
