Why Does My Furnace Smell When I First Turn It On?

After waking up to a particularly cool home on a September morning, you switch on your furnace and notice an unusual odor. While it’s sometimes normal to experience furnace smells when it’s first turned on, there are specific odors that indicate a problem. At Elkhorn Heating, Air Conditioning, Plumbing & Electrical, we can quickly diagnose your unusual odor and determine if it’s dust settling on the unit or something else.

If you smell gas, immediately evacuate the area without operating electrical switches or electronics. Once you are safely outside, call your utility provider’s emergency line or 911. Similarly, if you see smoke or fire, evacuate and call 911 before performing any of the following checks.

What the Different Odors May Mean

When dealing with furnace odors in Denver, it helps to consider the type of smell and when it occurs. While the odor description provides a strong clue about what is going on, it is not a diagnosis. For professional diagnostics, reach out to our experienced Comfort Specialists.

The following are some of the most common smells you may notice.

Mild Dusty Odor

If your heat smells like burning dust when it first starts up, that is probably exactly what the odor is. This is especially common at the end of fall and beginning of winter. Dust builds up in the furnace as it sits unused over the summer, leading to a furnace burning smell during the first use of the season. If this is the case, the smell should go away in a few minutes.

Persistent Burning or Plastic/Electrical Smells

A temporary burning odor at startup might not be an issue, but it’s an immediate concern if it doesn’t go away. Ongoing burning, hot plastic, or electrical smells can occur if the electrical components are overheating. Because of the potential fire and electrocution risks involved, you should immediately shut off your unit and call for repairs.

Sulfur or Rotten-Egg Odors

This is another smell that requires immediate action. Natural gas contains an additive that smells like rotten eggs so that it’s easier to detect leaks. If you notice a sulfur-like smell, there may be a gas leak in your system. You should immediately evacuate your home. Once everyone is in a safe area, call 911 or your gas utility’s emergency line.

Musty Scents

If your furnace produces a musty smell, it may be due to mildew or mold growth in your ductwork, vents, or blower compartment. To protect your family’s indoor air quality (IAQ), you should schedule an IAQ assessment and furnace inspection.

Carbon Monoxide Leaks

Carbon monoxide (CO) is an odorless, colorless gas. Because of this, you won’t be able to detect dangerous carbon monoxide from your furnace by smell. Even if your furnace does not produce any odor, you should schedule seasonal tune-ups to inspect the system for combustion, venting, and other safety issues. Additionally, test your home’s CO alarms monthly, replace batteries as needed if they are replaceable. You should also replace the alarms according to the manufacturer’s recommended service life.

Possible Causes Behind a Startup Smell

If a furnace smells when first turned on, there are several potential causes that could be responsible. Dust on heating surfaces, restricted airflow, overheating, electrical malfunctions, and motor problems can cause this symptom. 

While dampness, mold growth, and contamination are possible reasons for musty odors coming from your vents, they are not the only potential cause. Because of this, you should always have your system evaluated by a professional. The smell alone will not be enough to diagnose which part failed.

What Homeowners Can Safely Observe

As a homeowner, you should not do any troubleshooting if you hear an alarm, notice smoke or fire, or suspect gas. If it is safe to do so, you can use the following steps to safely observe the issue and rule out a few basic causes.

• Note when the odor occurs and any airflow or noise issues. Pay attention to whether it fades and returns.
• After turning your equipment off, you should inspect the filter and replace it with the correct type. 
• Check the return vents to see if they are blocked or obstructed. Do not open any equipment panels to do so.
• Never restart equipment repeatedly to reproduce the odor. You should also never clean burners, open the cabinet, test wiring, or adjust gas controls yourself. 
• Do not spray fragrance or cleaners into the vents. This will not fix the problem. 

After completing these basic checks, you can reach out to our team for a full diagnostic if the problem has not gone away.

When To Call for Service or Emergency Help

While a furnace smell after summer is sometimes a normal symptom, there are situations where emergency help may be needed. To protect your furnace, family, and home, use the following emergency response steps if you notice any concerning symptoms.

• Persistent, Unidentified Burning: In this situation, you should immediately stop the system if it is safe to do so. Do not keep operating it to see what happens. Once the unit is off, reach out for emergency repairs.
• Suspected Gas: If you suspect a gas leak, leave the area right away. Do not try to operate electrical switches, adjust the thermostat, use your phone, or do anything else that might cause a spark. Once all of the home’s occupants are at a safe outdoor location, you should call your gas utility’s emergency line or 911. Never try to find the leak yourself. Additionally, do not delay leaving in order to ventilate.
• CO Alarm or Suspected Exposure: If a CO alarm goes off or you suspect CO exposure, have everyone evacuate your home. Then, call 911.
• Smoke or Fire: For smoke or a fire, you should evacuate all of the home’s occupants. Then, call emergency services. Do not allow anyone to go back inside until emergency responders confirm that your home is safe.

After you have completed the appropriate steps, you can contact our Comfort Specialists for professional help. One of our technicians will come to your home to inspect your unit’s airflow, electrical condition, combustion, and overheating. Then, we will provide a no-pressure recommendation for solving the problem.

Frequently Asked Questions

Is a dusty smell normal when the furnace first starts? 

If your heater smells like burning dust when you first start it, the odor will likely go away. This type of odor can occur after downtime. After a few minutes, the dust buildup will burn off, and the odor should go away. If the odor remains, worsens, or is unfamiliar, you should have your furnace looked at by a professional.

How long should I wait for a furnace smell to go away? 

There is no universal waiting period for unusual odors. Instead, you need to consider what other signs are present and the type of odor. If you are unsure about the cause of the smell, you should reach out for help instead of waiting for the odor to go away.

What if my furnace smells like burning plastic? 

When a furnace smells like burning plastic, it may be due to overheated or melting electrical insulation, debris in the ductwork, or a faulty electrical component. No matter what the cause is, you should stop using the furnace if it is safe to do so. Then, immediately call for an inspection. 

Any indications of smoke, a fire, a CO alarm, or gas should be treated as an emergency. In this situation, you should immediately leave the area and call 911 or your utility provider.

Can I smell carbon monoxide from my furnace? 

No, you cannot. CO is an odorless gas, which is why homes have CO alarms installed to detect it. If your alarm goes off, you should immediately go outside and call emergency services. Do not try to investigate the problem or fix the furnace yourself.

Schedule a Furnace Inspection

If your furnace smells when first turned on, we can help. Our Comfort Specialists can evaluate your system and determine the cause of the odor. We offer upfront pricing and prompt services, so Denver and Littleton homeowners can get the support they need.

Reach out to schedule your next furnace inspection.