When It Rains, It Leaks: 3 Common Reasons for Rainy Day AC Leaks

Ginny Bartolone
Written by Ginny Bartolone
Updated November 18, 2021
living room with air conditioner on wall
Jodie Johnson - stock.adobe.com

It never fails—that sneaky AC leak creeps out every time it rains. Here's what to do about it

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There's nothing quite like a summer rainstorm to break the humidity and cool things down. But a rainy afternoon can quickly lose its charm when the water makes its way into your AC vent. There are a few reasons why water drips from an AC vent, including a leak in your home’s exterior and an HVAC malfunction. Here are some things to check for when investigating a leaky AC vent, and steps you can take to fix it, so that you can enjoy the pitter-patter of the rain from the dry comfort of your couch.

1. There's a Leak in Your Attic

By the time a leak becomes obvious, there's a strong possibility the water's been hanging out in your home for longer than you realized. For example, water dripping from your AC vent may have gotten there from another entry point.

In many cases, most of your AC vent investigation happens in your attic or close to your roof. When a roof leaks, the water can land on the ducts and make its way into any cracks or open seams. Eventually, it travels down your ducts and out the vent in your home.

What to Do About It

Head up into the attic and look for evidence of troublesome water damage. Telltale signs may include a musty smell, a damp area of wood or plaster, or patches of brown or black mold. If possible, head up during or just after rainfall to try to catch the source of the drip.

Remember, the leak itself may not come from a crack in the shingles, but rather broken or missing flashing around an attic vent. So, take extra care to inspect below any exhaust pipes or roof vent work. Water likes to travel—so it could be coming from further away than you'd expect.

2. High Winds Are Pushing Water Under Your Roofing

Driving rains—which are gusty rains during an intense storm—can test even the strongest roofs and ventilation systems.

If you notice that the rain only appears in your AC vent during a particularly drenching or windy storm, take note. It’s possible that the extreme wind could push water under your shingles or the protective flap in your attic vents.

What to Do About It

Take note if you detect water the next time you have a small-to-mid-sized storm. While you should always address any level of water damage, it could have been a one-time occurrence. 

It's also important to note if the water is coming through your bathroom fan. Your bathroom vent sends moisture to the outside of your home. Driving rains, poor flashing, or a broken vent could make it more susceptible to strong rainwater entering the wrong direction.

3. Your HVAC Is on the Fritz

There are a handful of reasons why your AC vents could leak without an outside water source like rain. Common issues include:

  • A clogged condensate drain line

  • Low refrigerant due to a leak

  • Frozen evaporator coils in the winter

  • Dirty air filters

  • Poorly installed drain pan

So, where did the water come from? Your AC removes moisture from the air as it cools it down but redirects it through a drain line and into a drain pan. Low refrigerant, clogged filters, or broken condensate parts will send the water in the wrong direction—often out of your vents.

What to Do About It

Begin by ruling out the direct connection to the rain. When you're several days past the last rainfall, look for signs of new water spots in and around your vents. If the water appears outside a storm, call your HVAC team ASAP for a look.

Who to Call When Rain Leaks From Your AC Vent

repairman inspecting air conditioner
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Figuring out the source of a leak is doable, and focusing your attention on your AC unit is a great way to narrow down the problem. The faster you find the leak, the better—no one wants to deal with the extensive cost of water damage.

The best way to start is to call a local HVAC specialist, as leaks can impact more than just your AC—they can affect your vent work, too. Additionally, you'll want to address the crack that allowed the water inside in the first place. 

If you or your HVAC team spot a leak in the roof, get a roofing team in for a thorough inspection. It's never worth climbing up on the roof yourself and risking a fall. If the pros locate a leak, your next step is to call a water damage restoration company to double-check for mold, wet drywall, or damaged insulation.

AC vent leaks can be concerning, especially if there's a wet and wild storm outside. Even the smallest leaks in our roof, eaves, or vents can cause problems over time, so don't be afraid to call in an expert for an extra look.

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