Troubleshooting Ride-Along: Why Is My Ductwork Leaking Water?

There are certain customer complaints that get your attention pretty quickly.

“My electric bill seems high” is one.

“My bedroom is a little warmer than the rest of the house” is another.

And then there’s:

“My ceiling collapsed.”

Yeah.

We’ll start there.

Customer Complaint

Part of the customer’s ceiling had collapsed underneath the ductwork.

The insulation above the damaged ceiling was completely saturated with water.

At first glance, this looks like a roof leak or plumbing problem. After all, there’s a lot of water above the ceiling, and air ducts aren’t exactly known for carrying water.

But this water wasn’t coming from inside the duct.

The duct itself was sweating.

A lot.

What We Knew Going In

This home had older metal ductwork running through the attic.

Metal ductwork isn’t automatically a problem. Properly installed and properly insulated metal duct can work just fine.

The problem was how this ductwork had been installed and what had happened to its insulation over the years.

Instead of being properly supported, sections of the metal duct were sitting directly on the roof trusses.

That matters more than you might think.

What We Checked First

Once we got into the attic, the condition of the duct insulation started telling the story.

In some places, contact with the trusses had torn or damaged the insulation.

In other places, the insulation wasn’t necessarily missing.

It had simply been crushed flat between the metal duct and the wood.

And insulation that’s supposed to be several inches thick doesn’t do much insulating when it’s smashed down to almost nothing.

The insulation above the ceiling was soaking wet.

So now the question became:

Why would an air duct make enough water to saturate insulation and eventually damage a ceiling?

Welcome to Florida.

Why Can Ductwork Make Water?

Your AC sends cold air through your ductwork.

That means the surface of the duct can get cold too.

Meanwhile, a Florida attic can be extremely hot and humid.

If that cold duct is properly insulated, the insulation keeps the warm, humid attic air away from the cold metal.

But when the insulation is missing, torn or compressed, that protection disappears.

Think about that cold glass of iced tea again.

Leave it outside and water starts forming on the outside.

The glass isn’t leaking.

The water came from the air around it.

Your ductwork can do exactly the same thing.

Except instead of a little puddle underneath your iced tea, this water can end up soaking insulation above your ceiling.

That’s considerably less refreshing.

What We Found

The metal duct itself wasn’t the real problem.

The insulation protecting it was.

Sections of duct had been sitting directly on the roof trusses. Over time, that contact damaged the insulation in some areas and severely compressed it in others.

Where the insulation was crushed, it effectively lost the insulating ability it was supposed to provide.

That allowed the cold metal duct to come into much closer thermal contact with the hot, humid attic conditions.

And cold metal surrounded by humid Florida air does what cold things tend to do in Florida:

It sweats.

The moisture continued accumulating until the insulation around and underneath the duct became saturated.

Eventually, enough water reached the ceiling below that the ceiling failed.

So when the customer said their ductwork was leaking water, they weren’t imagining anything.

There was absolutely water coming from the duct area.

It just wasn’t a leak from inside the duct.

It was condensation forming on the outside.

What We Ruled Out

This wasn’t simply a little condensation around an AC register.

It wasn’t a clogged AC drain spilling water into the attic.

And the duct wasn’t somehow carrying liquid water through the air-distribution system.

The location and condition of the ductwork pointed us to the insulation failure.

This also wasn’t something we were going to solve by wrapping a little tape around one wet spot and declaring victory.

Once duct insulation becomes extensively damaged and saturated, you’ve got a bigger problem.

What We Did

In this case, repairing individual sections didn’t make much sense.

The old metal ductwork and insulation were removed.

We then installed new ductwork and properly supported it so it wasn’t simply resting on the roof trusses and destroying the insulation protecting it.

That’s an important part of the repair.

Replacing wet insulation while recreating the same installation problem underneath it would just be scheduling a future appointment with ourselves.

We’re fond of repeat customers.

Just preferably not for the exact same failure.

Before We Left

The old sweating metal ductwork and saturated insulation had been removed and the affected duct system replaced.

The new ductwork was installed so the insulation could actually do its job instead of being crushed between cold duct and attic framing.

Because insulation only works when you let it be insulation.

Apparently that needed saying.

The Verdict

The customer’s ductwork wasn’t “leaking” in the traditional sense.

It was sweating badly enough to produce a significant amount of water.

Cold metal ductwork was running through a hot, humid Florida attic. Damaged and compressed insulation left portions of that metal without adequate protection from the attic conditions.

Moisture from the humid attic air condensed on those cold surfaces.

The surrounding insulation became saturated.

Eventually, the ceiling underneath it collapsed.

Same result from the homeowner’s perspective:

There’s water coming from my ductwork.

But finding out why matters considerably when you’re deciding how to fix it.

Other Reasons Your Ductwork Can Leak or Drip Water

This particular house had damaged and compressed duct insulation, but that’s not the only reason you might find water around your ducts or AC vents.

Damaged or missing duct insulation

This is essentially what happened on this call.

If insulation is torn, deteriorated, missing or crushed, the cold duct underneath can become exposed to warm, humid air.

Water can then form on the duct surface.

And you don’t necessarily need a giant missing section.

Sometimes a relatively small exposed cold spot is enough to sweat.

An extremely humid attic

Insulation helps separate the cold duct from the attic, but attic conditions still matter.

If unusually humid air is getting into an attic or other unconditioned space, condensation problems can become much more likely.

Florida already starts this game with the humidity setting on “ridiculous.”

We don’t need to help it.

Air leaks around the ductwork

Duct connections need to be properly sealed.

Air leaking from a cold supply duct can cool nearby surfaces. Depending on the temperature and humidity around those surfaces, that can create condensation where you don’t expect it.

This is one reason we don’t assume every wet spot means the duct insulation itself has failed.

Sweating around ceiling vents

Sometimes the duct in the attic is perfectly dry, but the homeowner sees water around a supply vent inside the house.

That’s a different clue.

The metal boot or register can become cold while warm, humid air reaches it from around the ceiling opening or from the room itself.

Same basic science.

Different location.

A frozen AC can create a lot of water when it thaws

If the indoor AC coil freezes, eventually all that ice has to melt.

Depending on where the water goes afterward, it can sometimes show up in places that make the original source less obvious.

The wet ceiling may be where the water ended up.

That doesn’t necessarily tell us where it started.

It may not be the ductwork at all

This is worth remembering anytime there’s water above a ceiling.

Roofs leak.

Plumbing leaks.

AC drains leak.

Water travels along framing.

And gravity has absolutely no respect for diagnostic convenience.

A wet ceiling underneath ductwork gives us a very good reason to inspect the ducts.

It doesn’t give us permission to skip everything else and announce:

“Yep. Ducts.”

What This Means for You

If you see water dripping from ductwork, water around a ceiling vent, wet insulation in the attic or staining on the ceiling underneath an AC duct, don’t ignore it.

And definitely don’t assume that because the AC is cooling, everything must be okay.

Your ductwork carries cold air through some very hot and humid parts of a Florida home. The insulation surrounding that duct is what keeps those two environments separated.

When that insulation fails, the duct can sweat just like a cold drink sitting outside.

A little condensation can become wet insulation.

Wet insulation can become saturated insulation.

And saturated insulation sitting above drywall can eventually become…

Your ceiling on the floor.

That’s generally the point where everyone agrees we should have dealt with it sooner.

The symptom tells us where to start:

“My ductwork is leaking water.”

The diagnosis still requires figuring out where that water is actually coming from and why.

Because the symptom isn’t the diagnosis.