We’ve all walked into our home at some point and noticed a foul or strange odor. Did your husband forget to take out the trash? Kids leave their soccer cleats out again? Is something on fire? It might be your heating and cooling system! Some smells can be frightening, like something is burning, and others just plain gross, like a dirty gym bag. Listed below are the four most common odors that can come from your HVAC system.

Mold or Mildew

We most commonly hear complaints about a mold or mildew odor. Some people say it smells like a gym locker or a dirty sock…hence the name “Dirty Sock Syndrome.” This smell typically occurs when your system is switched over from heat into cooling mode. After a long period without use, mold and bacteria can build up on your evaporator coil or drain pan.

Solution: Check your filters! Keeping your air filters clean can help reduce the chance of having a mold or mildew smell. Also, having regular preventative maintenance cleaning performed on coils and drain pans can help get rid of the odor. In some cases, coils need to be treated with a special spay or even replaced with an epoxy coated coil.


The first few times you run your HVAC system in heating mode, you will often notice a burning smell. Most times this is just the dust that has accumulated over the summer burning off the system. Let the system run for about 20 minutes and if the smell does not dissipate call an HVAC professional. Other burning smells are often described as a melting or electrical burning smell. This usually indicates a problem with the wiring or motors.

Solution: If you are just turning your heat on for the first time, wait a few minutes to see if the smell dissipates. If the odor smells more electrical or like something is melting, turn the system off immediately and call a licensed professional to come diagnose your HVAC system.

Rotten Egg

This is the most dangerous odor when it comes to your heating and air system. A sulfur or rotten egg smell indicates a gas leak! Turn the system off immediately, open your windows, do not operate anything electrical or with an open flame and evacuate! Natural and LP gas are naturally odorless but utility companies are required to add a chemical to give it a distinctive smell. Gas could be leaking from your furnace or it could be the gas piping and valves. Call Davis Heating & AC and your gas company right away!

Solution: Turn off and evacuate! Call an HVAC or your local gas company immediately!

Trash or Urine

A trash or urine smell coming from your vents could be a sign of critters getting into your duct system or HVAC equipment. Mice especially like to nest in and around the ductwork or system where its nice and warm. If your duct system is located in a crawl space, other animals like cats or possums can try to make a home. If an animal dies in your system or duct, you will quickly notice a trash or rotting smell.

Solution: Visually inspect your duct system and HVAC equipment for signs of animals. Be cautious if you try to remove the animal yourself! You can become seriously injured and/or electrocuted if you don’t know what you are doing. A service technician should be called out to repair any damage created by the critters and you may need to have a pest company come out to clear an infestation.

If you are in doubt about an odor coming out of your vents, always call! It is best to have your system serviced semi-annually as part of a preventative maintenance program, like our Energy Savings Club. This service includes a cleaning of your coils and drain lines as well as an inspection on the other components of your HVAC system. We can help to alert you to potential problems before they occur. Davis Heating & AC is known for being honest and dependable throughout Jacksonville, Richlands, Hubert, and the rest of Onslow County.