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Got Water Stains Around the AC Vents? Here’s Why

Were you admiring your ceiling when you noticed a discolored ring around your air vent?

You probably guessed it: something’s not right. Water stains around your vents are signs of other problems like rotting drywall or a mold infestation, so you’ll want to fix what’s causing the problem ASAP.

But don’t worry, we’re here to help. The main reasons we often see water stains around vents include:

  1. Not Enough Insulation Around Air Ducts
  2. Under-Insulated Duct Boot
  3. Air Leaks Around the Duct Boot or Vent

In this article, we’ll explain why you’re seeing these water stains and what you need to do to get rid of them, so you can have an unspotted ceiling in no time.

If you're worried your ventilation system may need an inspection, then schedule an appointment with one of our techs today.

Why Your AC Vents Have Water Stains Around Them

So why are you seeing these ugly stains around your vents in the first place?

Water stains around your air vents are caused by condensation. Here’s an easy way to think about it: You know those little drops of water that form on a cold glass on a hot afternoon? That’s condensation, and basically, it forms when warm air touches a cold surface.

The same process happens in your ductwork: Condensation forms when warm air from your attic meets the cold air from your air conditioner.

These little drops of water drip onto your ceiling, which eventually rots and discolors your drywall over time. In addition to being an eyesore, leaking water also damages your drywall and home’s insulation.

And because Florida air contains a high amount of moisture (humidity) to begin with, Tampa homes are especially susceptible to condensation problems with their ductwork.

Let’s take a look at what causes condensation in your ducts...

The 3 Causes of Condensation, and How to Stop Them

Cause #1: Not Enough Insulation Around Air Ducts

Insulated vs. uninsulated duct. Photo courtesy of Terry Brennan. Image source:

Ideally, your ducts should be well-insulated so that warm air from your attic or unconditioned space isn’t coming in contact with your AC’s cool air.

Solution: If your ducts aren’t insulated, you’ll need to have them wrapped in air duct insulation. And you’ll want a professional to do this job. According to, “qualified professionals should seal and insulate ducts in unconditioned spaces to ensure the use of appropriate sealing materials.”

Cause #2: Under-Insulated Duct Boot

If your duct boot (the metal connector between the air vent and your ducts) isn’t insulated, that could be what’s causing the water to drip into your ceiling.

Solution: Have a professional insulate the boot, ideally with fiberglass insulation to prevent warm air from reaching the boot’s cold metal.

Cause #3: Air Leaks Around the Duct Boot or Vent

A duct connecting to an air vent.

If there’s a leak around your air vent or your duct boot isn’t fitted correctly, then cold air escapes and mixes with the humid air to create condensation. The water from condensation drips onto your ceiling, and then the next thing you know, you have a water stain on your ceiling.

Solution: Have an HVAC technician inspect your air vent and ducts for leaks. If there are any leaks, they should be professionally sealed with a mastic sealer.

Getting Rid of Those Water Stains

First, you should have a professional get rid of what’s causing the root problem (that is, fixing the causes from the section above). If you don’t do that, no matter how many times you paint or remove stained drywall, it will just come back.

But once an HVAC expert fixes the problem, you can try applying a couple of coats of KILZ primer on your water stain, followed by your choice of paint and color. If that doesn’t work, look into some DIY steps to remove light water stains from your drywall. Otherwise, contact a professional for help.

Want to Get Rid of Those Water Stains? Do You Live in the Tampa Area?

Contact Red Cap Air Conditioning to schedule a ductwork inspection today. We’ll make sure your ducts are well-connected and insulated so that you won’t have to worry about any more water stains.

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