Nothing stinks like a mystery smell around the house. There's a reason homeowners tend to notice a sudden musty smell in the house during peak cooling season: Clogged filters, frozen evaporator coils, and other issues can increase energy consumption and raise a real stink if left unaddressed.

Put a stop to the stench with a quick inspection of your home's air conditioning system.

Why Does My House Smell Musty? 

There are many possible sources of a stale smell in any house, though all are likely caused by moisture. In most cases, it takes a fair bit of moisture to create a smell strong enough to permeate throughout your home. Some of the most common causes include:

  • Leaking pipes
  • Spills and messes
  • Roof or window leaks
  • High humidity in basements, attics, or bathrooms
  • Blocked or clogged drains

Homeowners can rule out these causes by looking for signs of mold, mildew, or water damage along walls or ceilings. Always contact a professional to remove mold, especially black mold.

Once you've inspected these areas of your home, it's time to take a closer look at your AC unit. You can often narrow down the source to your air conditioning system by asking yourself a few questions:

  • Does the house only smell when the AC is on?
  • Does the musty smell come from AC vents? Is the smell stronger near AC vents?

If the odor is more pungent when your AC is running, there's a very good chance your AC is to blame.

Related: How to Tell If Your AC Has Mold

Why Does My Air Conditioner Smell Musty? 

That unsavory smell has an equally repugnant source. Musty odors are usually caused by bacteria growth. Without proper maintenance, your AC system's dark, humid elements can be a ready-made home for bacteria, mold, and mildew.

Start your smell sleuthing by checking these likely problem spots:

  • Check the drain pan – Air conditioning units remove moisture from your home. Over time, that moisture collected in the drain pans. Usually, this moisture will evaporate before it's a problem. Units that haven't been serviced or have dirty filters are more likely to have issues with the drain pan. In most cases, you'll need to have the pan removed and cleaned to resolve the issue. Drain pans will always have water in them during the cooling season—this is normal. The problem is what can grow in this water over time. Regular maintenance and pan treatments (algaecides) can help keep the pan clean and free of any biological growth.
  • Frozen evaporator coil – AC units rely on airflow to absorb warm air and cycle cooled air back through return vents. Air filters remove airborne irritants like dust and dander but can get clogged if they aren't cleaned regularly. Clogged filters cause moisture buildup that can freeze the indoor unit's evaporator coils. When the water thaws, it can create a strong odor that‘s especially noticeable right when the AC unit turns back on. You'll need to thaw the system entirely and then replace the filters to resolve the problem.
  • Moisture in ductwork – Consistent high humidity levels can increase the risk of mold and mildew growth in your home's ductwork. Moisture in your ductwork could also be caused by a drainage leak. While not caused by your heating or cooling system, you may notice the musty smell once either system runs, as airflow pushes the scent throughout your home. If your HVAC's heat smells musty, as well as your AC, there's a good chance the source is in your ducts.

Your local One Hour Heating & Air Conditioning technician will need to inspect your ductwork to resolve the issue.

Preventing Musty Smells in HVAC Ducts and AC Units 

You can avoid these issues with regular professional maintenance, whether the source is in your AC or heat pump unit or ductwork.

There are also plenty of things you can do yourself, including:

  • Change your air filter every 1-3 months
  • Keep your home's humidity between 30-50%
  • Use a dehumidifier to combat seasonal changes in humidity, cooling, and moisture-related issues.

Punctual HVAC Services; Now That's a Breath of Fresh Air 

Count on One Hour Heating & Air Conditioning for professional HVAC diagnostics, inspections, and repairs when you need them most. Our friendly technicians identify the issue and make the fix promptly and with a smile. From getting to the bottom of smelly ACs to preventing issues in the first place, we’ve got you covered. Request an appointment or call (800) 893-3523 today.