Why Does The Furnace Smell Bad When You First Turn It On?

Many people wait to turn their furnaces on until it’s necessary each fall and winter. However, some people are shocked when they turn on the furnace and notice weird smells. So, why does the furnace smell bad when you first turn it on?

The furnace may smell bad when you first turn it on due to a buildup of dust, pet hair, and debris in your air ducts and furnace components. This can also happen if your furnace filter or air ducts are moldy, as mold can build up throughout the year. Turn your furnace off if you notice a rotten egg smell.

The rotten egg smell may indicate a gas leak, which is a serious emergency that requires professional intervention. Move to a safe location, then call emergency services, as you may put yourself at risk of serious injury if you stay. Follow along as we explore why your furnace smells bad when you first turn it on.

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

Whether it's due to manufacturing oils or moldy ductwork, you may notice weird furnace smells for many reasons. Like any other piece of HVAC equipment, a furnace is prone to problems that can contribute to bad odors at home. That said, the bad smell you notice when running the furnace is likely due to one of a few common reasons, including:

1. Burning Dust

HVAC systems collect a lot of dust, pet hair, and debris throughout the year. That said, you may not necessarily notice the smell of the dust as strongly when your air conditioner runs, since air conditioners provide cool air and don’t utilize any heating elements.

However, the dust that collects in your furnace is bound to burn when you finally run your furnace for the first time of the season. After a moment, the heating element will burn some of the dust and debris in your furnace, and the smell will permeate. Some people naturally panic and call an HVAC service right away, fearing a major problem.

The HVAC technician may ask a few questions and let you know that the smell is normal. Otherwise, they may play it safe and visit your home to inspect the system. Either way, you should expect a burning dust smell each fall when you run your furnace. The burnt hair and dust smell typically goes away within 10-15 minutes unless there’s another culprit.

2. Electrical Problems

Every renter or homeowner should familiarize themselves with the smell of burning electrical equipment and wires. That way, you know you’re dealing with an emergency when you notice this smell when you run the furnace. The smell of burning rubber and plastic can indicate that you have some burning electrical equipment and wiring.

A fishy smell can also indicate that the wire’s coating is burning or melting off, which is also scary. Unfortunately, you may not be aware of any electrical problems with your furnace if you haven’t run it in months. You may only find out about electrical problems when you first turn your furnace on.

Turn your furnace off right away if you notice a fishy, plastic, or burning rubber smell. This can indicate a serious emergency, and there is a big fire risk if you don’t act fast. Turn the furnace off and call an emergency HVAC line right away.

3. Mildew And Mold

HVAC systems are prone to mold and mildew, and that includes your furnace. Mold and mildew can grow on several furnace components and inside your air ducts and filter. This is common, as air ducts have the perfect environment for mold and mildew to thrive as they’re often dark, damp, and relatively warm throughout the year. That, paired with the dead skin cells and loose hair that enter air ducts, can contribute to mold. Moldy air ducts can contribute to mold throughout your home, as spores travel through vents.

That’s why it’s worth scheduling air duct cleanings every 3 to 5 years, or as needed. Otherwise, you’ll likely smell some mold and mildew burning off your furnace’s coils or spreading throughout your ductwork. Luckily, a musty, moldy odor isn’t typically an emergency, but you should still schedule an inspection to ensure it won’t spread.

4. Dead Animal

While somewhat rare, the bad smell you notice when first turning on the furnace could be due to a dead animal. That’s especially true if you live in a wooded area with lots of squirrels, opossums, raccoons, and mice. Unfortunately, animals sometimes enter homes through gaps and cracks and work their way into HVAC systems.

Once inside, rodents and other small animals often get stuck and eventually die. You may not notice the smell right away, as the decomposition rate varies based on many factors. For example, they may take longer to decompose if your house is cold and you’re still using the AC.

However, the animal will eventually decompose, and you will notice a foul odor coming from your vents. In some cases, this can coincide with you running your furnace for the first time of the year. Call a professional, as they have the protocols and equipment to safely remove dead animals.

5. Gas Leak

Turn your furnace off right away and leave your house if you smell rotten eggs when you first turn your furnace on. The smell of rotten eggs and sulphur can indicate a gas leak, which is dangerous. You must also dial 911 to reach emergency services or call your gas provider’s emergency line right away.

This problem won’t go away without intervention, and continually running your furnace can make things more dangerous. Don’t even run any other electronics in your home until professionals can intervene, fix the problem, and deem your house safe. Furnace gas leaks typically indicate that the heat exchanger, a key component, is cracked.

This can also happen if the gas valve, gas supply line, or thermocouple is damaged. Don’t attempt to diagnose the cause of the problem on your own, as it’s not worth the risk. Every minute you stay in the house is a risk, so leave it to the professionals.

6. Your Furnace Is New

Everyone knows about the new car smell, but have you heard of the new furnace smell? Like other HVAC equipment, furnaces are coated and treated with oil before they’re shipped out to customers and retailers. Naturally, these coatings will emit an odor when you turn your furnace on for the first time.

The lubricant and other coatings may emit a chemical smell when you run your furnace. It’s easy to panic when you notice this, but you must use context clues. The fact that your furnace is brand new should be enough to tell you it’s not likely an emergency.

However, you should still familiarize yourself with the other furnace odors we’ve mentioned in this guide. This makes ruling out other causes easier, but it’s typically caused by the furnace itself if you just had it installed. The HVAC technician who installs the furnace may even warn you about the smell.

Summing It Up

Bad furnace smells can indicate dust, debris, mold, and even dead animals in your air ducts. If your furnace is brand new, you’ll notice a chemical smell when you first turn it on, and that’s normal. However, you must turn your furnace off and call the gas company’s emergency line if you smell sulphur and rotting eggs. That points to a gas leak, which can be deadly.

Related Guides:

• Seven Tips To Help Your Furnace Work Better
• Why Does My Furnace Keep Tripping The Breaker