Effective and efficient heating may not be a concern of yours during the warmer seasons. However, once temperatures start to drop in the beginning of fall, you will turn your furnace on to start heating.

Certain furnace odors are completely normal when you first start heating your home. But lingering smells are concerning, since heating equipment is the second-highest cause of house fires. This guide will help you understand and deal with common furnace odors from the vents that stick around.

These most common furnace odors include:

  • Burning or metallic smell
  • Gas or rotten eggs
  • Dust
  • No smell but carbon monoxide detector going off
  • Damp or musty
  • Car exhaust

1. Furnace Smells Like Burning

When you first turn on your heating system in the fall, you might notice a burning smell from the furnace or a burning smell from the furnace vent. This is normal and not something to worry about, because your furnace can gather dust over the spring and summer.

As your furnace ignites to start heating, the dirt and dust burns off, flowing through the ductwork and eventually into your home. This smell typically goes away in a few minutes to a few hours.

Most experts recommend having the furnace and evaporator coil of your heating and cooling system cleaned before the heating season begins. This ensures all dust and debris is removed from the combustion chamber before it is burned off after starting the furnace. It’ll also keep that annoying burning dust smell at bay.

However, if this burning smell lingers, the furnace or its blower motor may be overheating. This is especially true if your furnace smells like electrical burning, hot plastic or burning plastic, which means wiring or components could be melting.

Most furnaces are designed to shut themselves down if they overheat. An electrical or mechanical issue may prevent this safety feature from working properly. The burning metallic smell may also indicate frayed wiring.

No matter what the cause, you should shut off your furnace immediately to prevent a potential house fire. Then contact an HVAC technician for furnace repair.

2. Furnace Smells Like Gas or Rotten Eggs

If you’re noticing a gas smell from your furnace, or your furnace room smells like rotten eggs, that smell is probably sulfur. This indicates you have a significant natural gas leak, because gas companies add this odor to alert you. Gas leaks could stem from a variety of issues, so having your system addressed by a licensed HVAC technician is imperative.

If you smell odors like this, turn off your gas supply via the shutoff valve, if you can do this safely. Then exit your house immediately, call 911 and your gas company. Exposure to natural gas may cause the following symptoms:

  • Headache
  • Dizziness
  • Nausea
  • Vomiting
  • Eye irritation
  • Nasal irritation
  • Breathing issues
  • Skin rashes and blisters

Seek out emergency medical care if you exhibit the above symptoms after noticing your furnace smells like gas. Without proper medical care, exposure to natural gas can be life threatening.

Less commonly, a furnace rotten egg smell can mean there’s not a problem with your furnace, but with your sewer lines. If your furnace smells like sewer, you might be smelling a dry sewer trap, which is located near your furnace. You can remedy this smell by pouring water down the floor drain in your basement.

Or you might be dealing with a sewer leak. Either way, a company that specializes in sewer lines can help you get to the bottom of this smelly problem quickly.

3. Furnace Smells Like Dust

Dirt and dust can be a problem when heating your home because they can build up inside your furnace, air ducts and air filter during the cooling season.

A dusty odor may also stem from a clogged filter that’s accumulated dust, dirt and other allergens that will flow through the ductwork and into your home along with the heated air.

If the filters are clogged with dirt and dust, conditioned air will not flow efficiently into your home. This not only leads to dusty air quality, but it also increases heating costs. Depending on the style of furnace filter you use, you’ll want to replace it every three to six months.

4. Furnace Doesn’t Smell but Carbon Monoxide Detector is Going Off

Not smelling anything but your carbon monoxide detector is going off? Your furnace may be leaking carbon monoxide, often due to a cracked heat exchanger.

A heat exchanger component exhausts gases naturally created during the heating process. If it breaks, carbon monoxide fumes can leak into your home and create a big problem, as this gas is colorless, tasteless and odorless. In some instances, a chemical smell from your furnace, like a sweet or formaldehyde-like odor, can be a sign it’s failing.

This part is designed to be durable and last for a furnace’s lifetime. Unfortunately, the metal is not made to last forever, and some things can cause it to fail sooner. Replacing a heat exchanger is expensive, so it’s usually best to do furnace installation if it fails.

Why Heat Exchangers Crack

Things that can cause yours to crack include:

  • Furnace is too big or too small for your home, which puts more stress on the metal.
  • Furnace is short cycling, or turning on and off frequently, which is constantly causing the metal to expand and contract.
  • Not changing your air filter frequently, which can make your furnace overheat.
  • Skipping annual maintenance, which can make your furnace work harder.

Carbon monoxide is fatal in large doses, so it’s important to have working detectors and have a heating professional do furnace maintenance each year. This allows an HVAC professional to spot problems with your furnace’s combustion chamber, along with other issues.

Having your furnace distribute carbon monoxide fumes is a serious problem that you can avoid with a regular maintenance schedule. Lakeside Heating & Air Conditioning offers affordable furnace maintenance in Denver, CO, and surrounding areas.

5. Furnace Smells Damp or Musty

If you notice a damp smell or musty smell when you come home, that may mean that water has seeped into the furnace. This strange smell coming from your furnace can happen at any time if there’s a loose hose connection on your furnace’s drain pan.

This furnace smell usually dissipates quickly after turning up the heat. But if it persists, you’ll want to contact an HVAC professional.

6. Furnace Smells Like Car Exhaust

If you smell car exhaust in your home or a strong odor from furnace exhaust, this usually means that there’s a problem with how your furnace is vented. Your furnace uses a vent pipe to get rid of gases that are created during the combustion process.

If you have a high-efficiency furnace, it’ll be vented with PVC pipe. Make sure this pipe is free of obstructions, like snow, ice or bird nests. Otherwise you risk having deadly gases like carbon monoxide spill back into your home.

Call Us for Affordable Furnace Repair

It’s always a good idea to have your heating system inspected professionally if you’re experiencing any strange furnace smells. If you’re wondering why your furnace smells like burning dust or plastic burning, it could be an indication that there is a serious problem with your HVAC system, and even small issues can lead to costly repairs. If you think one of these signs might apply to you, contact Lakeside Heating & Air Conditioning at 303-412-8015 or request an appointment online.