My Home’s HVAC Smells Musty and Nasty

South End Plumbing, Heating, & Air Expert Tips

HVAC Smells Musty and Nasty

A bad, musty odor coming from your HVAC system is unpleasant. It takes over the whole house. You probably don’t know what it is. All you really want is for it to go away or be fixed.

A musty, moldy, mildew, or damp smell from your air vents can be common, especially in a hot Carolina summer. There are multiple possible reasons the smell is invading your house. Some might require calling an expert technician to check and solve for you.

Does Your HVAC Smell Musty?

You can take on cleaning your HVAC system on your own. However, you should take some safety measures to prevent injury to yourself or damage to the system.

Here are some suggestions for removing the musty smell from your air:

  • Move the unit to an area where it will be secure while you work on it.
  • Be careful if you’re removing the outer case leading to the fans, coil, and compressor.
  • Flush and rinse the drip tray to remove all dirt and build-up. Do not, though, use too much pressure on the tray.
  • Blow compressed air from a safe distance so any inner components do not get damaged.
  • Clean fine dirt or pollen from the front or back of the unit with a small cloth or brush.
  • You can clean vents and ducts with a cleaning solution. Make sure to rinse the solution.
  • Let the unit dry for a couple of hours and clean it with a clean cloth. Let the unit dry before putting it back together.

Too Much Moisture in Ducts or Vents

Excess water gathering inside air ducts and vents can be brought on by either high moisture levels – as in humidity or condensation – or a leak going unnoticed. If you turn on the air conditioning and it’s musty a few seconds later, there’s a good likelihood mold and mildew are growing in the damp areas.

The HVAC smelling musty isn’t just an annoyance. Keep in mind mold exposure can create serious respiratory health problems. If you think it could be mold, you should call a professional to address the root of the problem and clean all the parts of the ducts and vents.

Full Drain Pan

This one’s about too much water, too. The moisture taken out of the air by your HVAC system has to go somewhere. The water runs out into a drain or drip pan.

This part of the system can get too full, have simple wear over a long period of time, or have nasty growth like mold. An ineffective, blocked, or dirty drip pan can stink. If left untreated, it’ll likely only get worse over time.

Does Outside HVAC Smell Musty?

The condensate line is a little PVC pipe beside the condenser system, which is part of the air conditioning unit located outside your home. Its job is to drain water from the drip pan to a drain. It’s also among the likely places for mold, mildew, and sludge to grow and stay due to its small dimension. This can lead to blockages will make the HVAC smell musty.

It’s recommended to clean the condensate line once a month. First, turn off the air conditioning unit at the thermostat and at the breaker box. Next, take the condenser line off of its attachment. Pour one cup of distilled white vinegar into the opening. Allow it to sit for 30 minutes. Rinse it with water to remove mold, dirt, and gunk. After that, reattach it to the exterior unit. Then you can turn the system on again.

bad-smells-duct-bowling-green-kentuckyEvaporator Coils Freezing

Air conditioning systems function by taking in the warm air as it rises inside a building, removing moisture from it, cooling it, and sending it down through vents. Free-flowing air is essential for this process, so clean air filters are a vital part of a well-running system. Changing filters every 1-2 months is recommended.

Dirty or clogged filters obstruct airflow. When there’s poor airflow, water condenses on and collects around and on the evaporator coils. Evaporator coils hold refrigerant. They cool the air just before it runs through the vents back into the house. Moisture on the coils can freeze. This can end up as a bigger problem than just a bad smell.

The AC Unit is the Wrong Size

For your air conditioning system to function efficiently, it needs to be the right dimension for the area it’s supposed to cover. If it’s too big for your home, the air gets cycled through the building too fast. The moisture in the air doesn’t evaporate fully and there’s excess moisture that ends up somewhere. The wrong HVAC unit dimension might also result in the system turning on and off continuously. This issue leads to extreme wear and tear, increase energy bills, and possible system failure.

Have a cooling and heating professional check if your air conditioning system is the best, most efficient size. HVAC unit sizing considers factors such as a home’s square footage, the environment, the number of people, insulation, and ceiling elevation.


At South End Heating and Air, we specialize in HVAC and furnace repair, call us for a free consult. We’ll evaluate your system and help make recommendations for optimum value. After all, we want to keep you cool all summer long and warm in the winter. Just schedule a visit with one of our technicians to talk about how we can help with your heating needs. Would you like to learn more options our techs can help you with? give us a call 704-684-5339

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