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The A/C Guy of Tampa Bay Inc. Blog

Why Does My House Smell Like Mildew Out of Nowhere?


You turn on your air conditioner, walk through your home, and a minute later you smell something. It immediately catches your attention and won’t let it go: a rancid smell in every single room.

At least, every room in your home with a vent. That odor is mildew: a disgusting fungus that thrives on dark, moist conditions. It can begin in the winter when the heater is on, and get worse in the summer when you turn your air conditioner on.

To vanquish the mildew smell coming from vents, you’ll need professional services. If you want to prevent mildew growth in the future, this is what you need to know.

Trapped Moisture

Moisture leads to mold and mildew growth. This growth can occur in drywall, paper products, carpeting, and even dust. However, these problems present themselves differently than when it’s in your ductwork.

When you have leaks in your ductwork that allow heat and moisture to travel freely between the vents and dark spaces in your home (such as your walls and attic), you have a big problem on your hands.

Forced air makes it difficult to give mold and mildew the right environment to grow. There will be some level of humidity in your vents, but leaving your fan on its auto setting keeps air moving and prevents mildew buildup.

It’s important to keep in mind that because mold and mildew can grow in dust, dirty ducts with thick dust can become hosts for this kind of growth. Then when you turn your air conditioner or heater on, those odors get blasted through your vents.

Poor Airflow Across Your Home

Even if there is no mildew present in your vents, the smell of mildew can still occur. This is called stale air: when air remains in one area for a long time and builds up pollutants and particles.

Stale air doesn’t just smell bad, but over time if it continues to build up, it can cause health problems. Stale air is a product of poor air circulation across your household.

Debris in Your Air Conditioner Ductwork

Debris in your air ducts refers to dust, dirt, building debris, and allergens that build up over time. This can contribute to mildew growth, but in general, blowing these particles through your vents and into your living space can produce a bad smell on its own.

It depends on the type of debris in your ductwork. It’s also important to note that critters can find their way into your ducts (by chewing through the material) and unfortunately die, which will produce its own odors that you’ll be able to smell when you turn your heater or air conditioner on.

You Deserve a Better Smelling Home

The stench of mildew points to a larger problem. Your vents should be clear from mildew and mold growth; you simply deserve a better smelling home when you turn your air conditioner on. Professional mold and mildew removal is the solution you need.

Contact The A/C Guy of Tampa Bay Inc. today for mold and mildew concerns and learn what we can do for you and your home as soon as possible.

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