What’s That Smell Coming From My Furnace? Here's What You Need to Know

A strange smell coming from your furnace or heater is never a welcome surprise. But before you panic, let’s figure out what’s causing it and whether you need to take action.

In this guide, we’ll cover the most common furnace smells, what they mean, and when it’s time to call in the pros.

Key Takeaways

• A burning smell when first turning on your furnace is often just dust burning off, but if it lasts longer than 24 hours, turn off the system and call a professional.
• A musty or moldy smell could mean mold or mildew in your furnace or ducts, which could become a health concern.
• A rotten egg smell is a sign of a gas leak. Leave your home immediately and contact your gas company and an HVAC technician.

Now, let’s take a deeper dive into what each smell could mean for your furnace or heater.

Burning Smell: Dust or Something More?

If you notice a burning smell when you turn on your furnace for the first time in a while, don’t worry right away. It’s fairly common for dust to accumulate on the heat exchanger when your furnace hasn’t been used for months. When the system heats up, it burns off the dust, causing that brief burning odor.

However, if the burning smell continues beyond the first 24 hours of running the furnace, it’s time to take action. Prolonged burning odors could indicate:

• Overheating components
• Electrical issues
• Melting parts inside the system

In this case, it’s important to turn off your furnace immediately, shut off the gas, and contact an HVAC technician. Waiting could lead to more serious damage or even a fire hazard.

Musty or Moldy Smell: A Sign of Mold or Mildew

A musty or moldy odor coming from your furnace or heater is never a good sign. It usually points to the presence of mold or mildew either inside your system or in your ducts. While mold is less common in dry climates like Arizona, it can still develop, especially during humid times like monsoon season.

Ignoring mold or mildew can lead to:

• Poor air quality
• Respiratory issues
• Unpleasant odors throughout your home

If you detect this smell, it’s essential to investigate the issue before it escalates. Mold can spread quickly and create a serious health risk for you and your family. Contact an HVAC professional to assess the situation and clean your system if necessary.

Rotten Egg Smell: A Potential Gas Leak

A rotten egg smell is the most alarming of furnace odors, as it usually indicates a gas leak. Natural gas is odorless, but utility companies add a sulfur-like scent to help homeowners detect leaks.

If you notice this smell—especially if it’s stronger near your furnace—follow these steps immediately:

1. Evacuate your home and make sure all household members get out safely.
2. Do not use any electronics or anything that could ignite a spark.
3. Call your gas company and then contact an HVAC technician for emergency assistance.

A gas leak is dangerous and can lead to explosions, so it’s crucial to act fast. Never try to fix this issue on your own.

When Should You Call a Professional?

While some furnace smells are harmless and short-lived, others can indicate serious problems that require professional help. If you experience any of the following:

• A burning smell that lasts more than 24 hours
• A musty or moldy odor that persists
• A rotten egg smell (gas leak)

Don’t hesitate to contact Parker & Sons. Our team can diagnose and resolve any furnace issues to ensure your home is safe and comfortable.