Skip to Content

10 Reasons Why Your Furnace Smells Like Rotten Eggs

As a homeowner, you would love your home to be tranquil and a place of refuge. So you set up a furnace for the cold nights of the fall and winter, and all is well. However, recently your furnace has been giving off a nasty smell like rotten eggs or gas, and you’re disturbed by it.

There are several reasons why your furnace smells like that. To find the solution to the rotten egg smell, visit this site.

Here are the reasons why your furnace smells like rotten eggs:

Cracked Components

Your home furnace as a unit could last appreciably longer than most of its parts. For example, a significant number of home furnaces suffer from cracked heat exchangers. The moment a heat exchanger gets any damage, that crack or hole releases a putrid smell similar to formaldehyde, which is why your furnace smells like rotten eggs.

We suggest replacing your heat exchanger immediately if that is the case. That problem could lead to your home furnace being inefficient and a fire outbreak. Carbon monoxide problems could also arise.


If your home furnace is in a damp part of your home, this dampness could settle on the furnace unit. When you finally light the furnace, it turns on and gets hot. The moisture begins to evaporate, creating a smell of dampness throughout your home.

If this is the case, you’re lucky. This odor may resolve itself as the furnace continues to burn.

Excess dust

During summer, while your furnace is dormant, dust could accumulate inside and outside of your furnace. So when you finally heat up your home in the winter and fall for the first time in the year, the furnace burns this dust. If your warm house smells like gas for a short period, chances are the odor will fade shortly.

To prevent this unwanted smell, you can dust your furnace before you switch it on for the on-season

Gas leaks

Natural gas used for heating is laced with sulfur to give it a rather distinct odor of rotten eggs. Adding sulfur is done to alert the homeowners of any gas leaks, if there are any. If your furnace smells like rotten eggs, leave the area and call an HVAC technician and your gas company.

Possible Contaminated air intake

Most furnace units installed today intakes air from the outside of your home. Meaning that anything close to this intake system is most likely to change the smell of the heated air in your home. An example could be if your furnace is smelling like sewage; chances are the odor is likely coming from a sewer opening close to your air intake system. Please be sure to look at the area surrounding your air intake vent.


In a few situations, mold could grow on your damp furnace. Mold on furnaces is very common in places with higher humidity and in homes where the furnace unit stays cool and moist. Mold could smell a little similar to the smell of rotten eggs or gas, but the scent generally doesn’t go away as quickly as you’d expect it. Mold could also smell quite musty or earthy. Chances are your oil furnace smells like rotten eggs because of mold.


If there’s an obstruction in your home furnace unit, one of the initial signs that you’ll likely notice is the change in the smell of the air coming out of it. The scent of the air coming out of your furnace depends on the type of obstruction in the unit. For example, an obstacle in the chimney could make your furnace smell like smoke, while a rodent stuck in the furnace unit would smell like decay or rot. Once this happens, you’ll have to turn off the system and get it inspected to resolve these underlying issues without the risk of poor furnace venting that could lead to carbon monoxide buildup in your home.

Old filters

Your furnace is fitted with internal filters that help maintain the excellent air quality in your home. After an extended period, the filter may become clogged with dirt, pollen, or even mold and debris. Not only will an aged air filter hamper the efficiency of your furnace, but you will smell the dirt buildup as well.

An old furnace filter, sometimes, could smell like motor oil. However, if replacing the filter does not stop the smell, the unit could have a significant oil leak, which requires professional attention. Contact an HVAC service to thoroughly check your furnace to avoid further damage to your furnace.


Besides the gas leak-related odors discussed in the fourth section, you cannot, under any circumstance, ignore electrical, hot metal, or other such odors coming from your furnace unit, as these make your electric furnace smell like rotten eggs.

These odors are a typical indication of a problem related to overheating and could mean a faulty auto-shutoff. Unless you’re an HVAC specialist, do not attempt to fix an electrical problem. You could get electrocuted.

Vent contamination

Similar to the area around your outdoor intake system, what surrounds your indoor vents can affect your furnace’s smell. Some of the prevalent vent contamination disturbances are pet hair or urine odor. Look around each vent opening for pet excretion that needs cleaning. Taking care of this mess should resolve the smell.

In place of the information provided, we strongly recommend that you consult an HVAC expert within your area of residence if you have any worries about the odor coming from your furnace. For example, if the smell appears out of the blue, is very pervasive, or persists for an extended period, you could need a licensed technician to help determine the actual underlying cause of the odor and get it fixed immediately.


This guide is just that, a guide. You’ll require the experience of your trusted HVAC professional to help you decide on the proper course of action the moment your furnace starts to smell foul.





Jeff Campbell