Furnace Odors

furnace odors

Furnace Smells You Should Never Ignore

When you run your furnace, you expect it to provide clean fresh air throughout your home. The last thing you would expect is to notice strange furnace odors. It could be an overwhelming odor, or a faint whiff making you wonder at first if it is coming from the furnace. Unfortunately, the furnace can produce odors some harmless, but other furnace smells you should never ignore. Some furnace odors are indicators of impending or ongoing furnace issues and the need for immediate HVAC service. To ensure your furnace operates properly and your family stays safe in this article we discuss the most common furnace odors you may encounter and the causes behind them.

Rotten Eggs or Sulfur

Natural gas is odorless and colorless making it nearly impossible to detect. Unfortunately, natural gas is also dangerous when inhaled, causing dizziness, nausea, fatigue, and irregular breathing. For this reason, many utility companies add a chemical called methyl mercaptan to the gas as a safety precaution. Methyl mercaptan is also colorless, but it creates an odor like rotten eggs. A rotten eggs or sulfur odor is a sign that there is a gas leak. If you notice this smell after turning on your furnace, turn it off and leave your home immediately. Contact your gas company or fire department to shut off the gas supply and trace source of the leak. If the furnace is to blame, contact an HVAC professional for repair.

Dirty Socks

An odor similar to that of dirty socks occurs when bacteria builds up on the heating system coils. The constant cycle between cool outdoor temperature and reheating when thermostat is turned up results in condensation buildup and a moist environment causing bacterial growth. The best way to remedy this odor is cleaning. It is important to keep up with routine maintenance so an HVAC technician can thoroughly inspect and clean your unit.

Burning Dust

When you have not used your furnace for a while, you may notice a burning dust smell. It may be particularly strong at the start of the winter season, but the more you use the furnace it will gradually begin to fade. However, if the problem persists try changing the air filter, it may be clogged and allowing dust and dirt to reach the motor. If changing the filter does not help, then it may indicate a more serious issue with the furnace. In this case, turn the furnace off and contact us at LA Construction, Heating and Air.  

Plastic, Electrical or Metallic

You might smell plastic, electrical or a metallic odor coming from your furnace if it overheats or a furnace component is overheating. As your furnace ages, worn bearings could cause issues with the blower motor. As the furnace tries to continue operating, it could cause excessive heat buildup in the motor. The heat could melt away wire insulation resulting in shorts or sparks.  The odor comes from these components, wires getting melted away due the short or other malfunction. This is one smell you should not ignore. If you were to continue operating the furnace under these conditions, it could lead to further electrical damage, risk of shock or the sparks could cause a fire. If you smell any of these odors that suggest something is burning, cut the power to the furnace and contact a professional immediately.


At the beginning of the season your furnace could also produce a musty odor. A filter that is not frequently replaced or clogged could cause the furnace to smell musty. Like the burning dust odor, this odor should go away within a few cycles as the heating should eliminate any dampness. However, if the odor does not fade, you may be dealing with mold or mildew. Contact our team to inspect your furnace and ductwork.


If you ever notice a distinct chemical odor or formaldehyde, this is one of the most dangerous furnace odors you could experience in your home. This type of odor could signal a cracked heat exchanger which could increase the risk of fire or carbon monoxide poisoning. Turn your unit off and contact us immediately for an inspection of your system.


A smoke odor could be a sign that the flue pipe or exhaust vent is blocked. If blocked the furnace combustion will have nowhere else to go than your ductwork. If the odor is faint open windows to ventilate your home, but if it continues shut furnace off and wait for a professional to asses and identify the source of the smoke odor.


If you notice a sewage odor coming from the vents it may be that a sewer system opening is near the intake system.  A quick inspection of the external vents can help you identify the source of the smell, but you may need to contact a plumber to resolve the issue.

Contact LA Construction, Heating and Air

If you notice any of the above odors do not ignore it and contact our team at LA Construction, Heating and Air. We can perform furnace repairs or schedule routine maintenance for your system. Give us a call at 818-341-3406 or contact us online, we are here to help you stay warm and safe in your home.

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How To Reduce Indoor Humidity

To reduce indoor humidity use a dehumidifier, replace AC air filters, avoid condensation and schedule routine AC maintenance. When humidity levels are right you will feel more comfortable in your home leading to lower heating and cooling bills year-round. Furthermore, humidity is a contributing factor to health concerns such as allergies, poor indoor air quality and contributes to mold growth.

Signs You Need AC Repair

Most of the time your system will indicate there is an AC issue before it breaks down. It is best not to postpone AC repair, because it will cause unnecessary wear and tear on your system and possibly lead to a complete breakdown requiring AC replacement. Lack of cool air, increased energy costs, unusual sounds and smells are among some of the signs you need AC repair.

Poor AC Airflow

Airflow issues can result in hot and cold spots, pressure imbalances, ac not cooling, or low airflow from the vents. Ignoring poor ac airflow issues for too long can put unnecessary wear and tear on your system and lead to compressor failure. If you are noticing any issues with your AC this summer give us a call or contact us online for AC repair services. We also offer preventative maintenance plans.