8 Smells Coming From Your Furnace That You Should Never Ignore

Yuck! The autumn chill is here and you just turned on the furnace for that cozy, warm air, only to be greeted with a stinky smell. An odor in your home is unpleasant enough, but when it comes from the furnace, it can be quite startling. Some furnace smells aren't uncommon, especially if you haven't run it for a while. Still, other times, an odor could waft through the home that could be a major red flag for your furnace that you should never ignore. The odor may be from something simple like an air filter, but other causes can be overheating components, melting wires, a gas leak, and other serious issues. For the best health and safety of your home, you should contact a professional HVAC repair service for a complete inspection.

Like all home appliances, furnaces can suffer breakdowns or issues, so they do require maintenance to keep running. If you often neglect maintenance tasks, such as scheduling an annual inspection or not changing your filter regularly, it might result in problems building up in your system. That neglect can start to show over time, announcing itself with weird smells. Sometimes, the issue may be with your blower motor, filter, or wiring, or overheating. For gas furnaces, the smell might accompany other signs of a carbon monoxide leak. Even if these smells may seem minor, they still warrant an inspection to ensure you can operate your furnace safely this season so you can enjoy your furnace without worry.

Turning on your furnace for the first time, you might smell dust burning. This odor comes from dust buildup on the heat exchanger and other components, gradually fading away as it burns off after a while. If the smell lingers for several hours, it may point to a deeper issue. A dirty air filter, particularly one clogged with pet dander and debris, can struggle with air circulation, pushing the dust around the unit. Try replacing your filter, and if that doesn't fix the problem, contact an HVAC service to check it out.

Did you know an unexpected reason your house smells musty can be your furnace? If there's a little moisture near the unit when you first turn it on, you might smell a brief musty odor that disappears. The lingering mustiness shouldn't be ignored though, as you might have mold spores and mildew in your air filter, or even worse, infecting the system. You can try changing the air filter if it's been a while, but you should contact professionals to guard against a full-blown mold takeover.

When you notice your furnace has the distinct smell of chemicals such as formaldehyde, this likely indicates you have a problem with your heat exchanger. The heat exchanger is a crucial element in your furnace, absorbing the cool air, warming it, then distributing it throughout your home. The smell of chemicals coming from a furnace often means it is cracked, which requires immediate attention. A cracked heat exchanger can emit carbon monoxide and other gases, so turn off the furnace, open the windows, and wait for a professional to address the situation.

Burning plastic odors can be a sign of overheating, but it may also be from a foreign object falling in the ducts. Perhaps your child pushed a small toy into the vent, and now it's melting as the furnace circulates warm air. Turn off the system, then check your vents for any loose objects. If you don't find anything, then it may be from loose wiring or an electrical short, with the smell originating from the wires' insulation burning. Contact an HVAC tech for an inspection to avoid damaging your system or causing a fire hazard.

Smells of rotten eggs (sulfur) are huge warning signs for your gas furnace. Gas lacks an odor, so companies add a chemical odorant in case of a gas leak. Take action immediately and evacuate. Open your windows to air out the home, then call 911, your gas company, or the fire station for assistance. If you live in an apartment or condo, notify your neighbors of the odor as well. If you don't have a gas furnace and yet still notice a sulfuric odor, it may be a plumbing issue.

The air from in home smelling like car exhaust likely means your furnace's exhaust pipe is blocked, so it can't correctly vent the gases created during the combustion process. The blockage may come from debris or bird nests lodged in the exhaust pipe, meaning the gases flow back into your home. Open your home's windows immediately to introduce fresh air and call for emergency service to help prevent falling ill or suffering fatality from carbon monoxide poisoning.

Furnaces with sewage smells may be warning signs of a gas leak in your home or a problem with the condensate drain line. This part carries water vapor away from your furnace after the system creates it during the fuel burning process. If you smell the stench of sewage and notice pooled water, you likely have a clog or blockage. However, because the problem may also be a nearby cracked sewage line, it's important you have a professional check it out as soon as possible to avoid getting sick from methane gas.

A dirty air filter in your furnace can cause a lot of problems, including creating a smoke smell. Swap out your clogged air filter for a new one and see if the odor lingers or dissipates. Another possibility is that your furnace currently has an overheated motor, which creates the smoke smell as it struggles to keep up to the desired temperature. Because it could be any of these issues or a more serious electrical problem with your furnace, you shouldn't ignore it. Instead, power it down and call an HVAC tech.