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  • Writer's pictureJake Overdiek

What causes your HVAC system to smell bad?

Updated: Apr 12, 2023

Imagine after a long day of work, coming home and smelling a horrible odor. You wonder what is causing the odor and begin to sniff around. Your AC is running and the smell is now circulating throughout your home. The smell might be stronger in one room compared to others, or so you think. You look around your home trying to find the source, realizing it is permeating everywhere. That’s when you realize it might be coming from your HVAC system.


If your HVAC system smells bad, there could be a wide range of issues causing it, and it’s something you need to get taken care of as soon as possible. After all, you’re not sure that whatever is causing the smell, could make you or your family sick, wreak havoc on your HVAC system, and cost you a lot of money to fix if it’s not taken care of the right way.


Let’s look at potential causes when you have bad smells coming from your HVAC system, and how to eradicate these odors.


Reasons why your HVAC system might smell bad


Feet, Dirty Socks, or Locker Room Smells

  • We’re not kidding here. You’re probably all too familiar with the overwhelming smell of sweaty feet, dirty socks, old cheese and corn chips, but you might never expect these locker-room smells to come from your HVAC system. If your HVAC system smells like feet, you’re most likely dealing with an extremely dirty and clogged-up evaporator coil within your AC system. Dirty sock syndrome occurs when bacteria build up on your evaporator coils. This is typically caused by condensation buildup, and the moist environment in the coil, resulting in bacterial growth. This typically starts with an AC system that’s not draining properly so that water and all the dirt and debris within it starts pooling up and festering. This will cause the locker room and dirty feet smell.

Dust or Musty Smells

  • When the initial cold weather hits and we switch from using our AC every day to needing our heater, you may smell a dusty burning or musty attic smell on the first few uses of your heating system. This will fade gradually as this is a normal thing when the furnace/heater is not used for quite some time. This musty smell occurs when dust, dirt, and other debris collect on your unit and in your air ducts. As your furnace warms, the dust and dirt may burn away and smell faintly of smoke. Though the smell may seem worrisome, you don’t have to panic about damage to your unit or home. However, if the smell persists, you could have a clogged filter that allows dust and dirt to reach your furnace.

Continuous Burning or Gunpowder Smells

  • It’s best practice if you smell burning to shut off your HVAC system before beginning to investigate the cause of the smell. If you suspect a fire, call 911. If you don’t see any signs of a fire, and you feel like it’s safe to investigate the cause of the smell, start by going to the location of your indoor unit (attic or closet) and take a whiff around. If you can smell burning or a gunpowder smell from the unit, chances are the circuit board or fan motor has or is in the process of shorting out.

Skunk, Rotten Eggs, or a Gas Smell

  • This smell is the most alarming one on the list. More often than not, this indicates leakage of gas within the HVAC system, specifically, Methyl Mercaptan. Natural gas on its own is odorless and utilities and gas distributors put Methyl Mercaptan to provide a distinctive odor to it. This ensures immediate detection to prevent any serious harm that can occur from gas leakage. If your AC smells a lot like skunk spray, you won’t be mistaken. This means that gas is leaking and getting into your ductwork. At the first sign of such a smell, immediately turn off your gas supply. Then contact your utility company, who will detect the source and repair the problem.


What can you do about HVAC Smells?


There are a few things you can do to reduce your HVAC pushing different smells through your home.


Change your HVAC filters on a regular basis. Depending on the type of filter and what is in the home you may need to change the filters monthly or as little as ever 6 months. Best practice is to change the filters based on manufacturer guidelines and you can consult with your trusted HVAC company.

  1. Use exhaust fans when cooking, cleaning and showering. This will help release chemicals, moisture, and other smells outdoors instead of letting them get into your vents.

  2. Wipe down counters, appliances, dust, vacuum, and regularly sweep, as well as wash your linens and towels regularly to keep smells and debris from getting moved around your home by your HVAC system.

  3. Consider having an air purifier system installed on your HVAC system.

  4. Call Uni-Serve Air Conditioning and enroll in our Uni-Shield routine maintenance for your HVAC system to ensure your system is performing at peak efficiency.


So, what should you do if your system smells bad? The first recommendation is to change the air filter. This does help with a variety of issues, including bad smells. If the smell persists, it’s time to call your trusted HVAC professionals at Uni-Serve Air Conditioning to come out and diagnose what’s going on with your system. We recommend our Uni-Shield maintenance program and will work with you to determine the best scheduling for your home. We help shield against system outages by maintaining your HVAC system. Call us today and see how we can keep you comfortable and protect against bad smells.


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