Questions & answers about the cause, risks, and repair of conditions that cause water, condensate, or ice formation in air conditioning or heating ductwork.

Page top photo: mud stains confirm that this HVAC duct has been flooded.

This article series explains the causes and cures for problems of condensation, water, or ice formation in heating or air conditioning system duct work.

Q&A on Causes & Repair of Condensation, Water or Ice in Duct Work

Building floods may wet HVAC duct interiors, especially ducts located on lower building floors or in basements and crawl spaces.

Our photo above shows mud in the metal duct work in a residential basement of a home that had been flooded.

Following flood exposure metal ductwork should be inspected, cleaned, and sanitized.

Flex-duct that has been wet for any reason should be replaced.ease of fiberglass fragments into building air).

Question: What product will fix the water leak in this exhaust vent

Please observe the below issue Water leakage in exhaust duct (MS metal flange),

Please suggest the Suitable solution for below issue in your product. - HG by private email, India

Moderator reply: find and fix the condensate or leak source of water in the exhaust vent

Sorry, but we cannot provide a product or service that will solve the water dripping in the exhaust vent in your photo.

In my opinion, no individual "product" would be the proper solution for this problem.

Instead, and having to speak generally as we have no information even about the kind of exhaust vent in your photo, my advice is to find the leak or mis-routing of condensate or missing insulating causing the condensate formation where it should not.

More details about these issues are

at WATER & ICE IN DUCT WORK.

Please also see WET CORRODED DUCT WORK

We do not sell anything. No products, no services.

InspectAPedia.com provides building and environmental diagnostic and repair information.

In order to absolutely assure our readers that we write and report without bias we do not sell any products nor do we have any business or financial relationships that could create such conflicts of interest.

Flex duct and rigid duct run in 10" space between floor and ground surface

We have a house built in the 20's that does not have conventional drain tile and sure foundation (mortared stone coated in concrete).

Under-house flex and rigid duct was dug into the 10" clearance between ground and joists. Of course, flooding ruined it all.

I have dug out the crawl to 40" clearance, leaving three feet support around load-bearing walls. I have removed all duct, insulation, and plastic. I am now looking to replace the duct (I will also install sumps). Fearing more flooding, I have talked with an HVAC installer that has recommended BlueDuct--expensive, but leakproof.

I am willing to pay the price, but there are two questions I have: I see no information on BlueDuct being used without being buried; and the cost is so prohibitive that I can replace the conventional ductwork twice for the price of BlueDuct! Any ideas would be helpful. On 2019-03-19 by JumbliahJones -

Reply by (mod) -

OPINION: I would not bury ducts below grade, nor run ducts in an inaccessile 10-inch space under a floor where I could never access, replace, repair, or clean them - period. The chance that those ducts would never need to be accessed over the future life of the building is zero.

Question: Cause of water at the air return vent

What makes the water from an air conditioner build up in the return vent? - Connie Woyan

Reply:

Connie: if you see water at the return vent it may be condensation on a cool surface, or it could be condensate leaking down into the return vent from your air handler.

You'll need to make a closer inspection of the air handler (blower unit) itself.

 

How to assess and fix wet attic ductwork after a Hurricane?

We had water blow in through the attic during hurricane Florence which collapsed several areas of the ceiling. We have a hvac return in the attic. We're sure the return was wet during the 3 days the storm hung over the area.

Also with the collapsed ceilings we had water that soaked carpet and flooring and we are fearful the water drained in through the duct registers. How can we get this assessed so insurance will cover a new system if the air handler got wet as well as the ductwork - On 2018-12-12 by Jo Ann

Reply by (mod) - had water blow in through the attic during hurricane Florence

Jo Ann You'll need an onsite inspection that makes an actual visual assessment of all of the materials involved - one that your insurance company will accept.

Generally soaked wall to wall carpet, drywall, insulation, are replaced, and possibly ductwork, depending on what material was used and whether or not it can be cleaned.

When it rains ground water leaks into our ductwork under the floor slab. What's the best fix.

Situation: my house's return air is in the concrete foundation/slab.

Problem is that with heavy rain, the ground water leaks through/in this return air duct work. I don't have a USB inspection endoscope to locate the exact source, but my main question comes down to repair, what's the most cost-effective solution?

I want to avoid busting up the concrete to replace anything, but don't really want to fill the return air with concrete and put a new system in the attic for fear of $$.

Isn't there a spray that can reseal the return air? On 2018-01-12 by JB

Reply by (mod) - return air is in the concrete foundation/slab - water leaks in

JB

Take a look at SLAB DUCTWORK

There are indeed duct lining sprays but not I nor any expert with whom I have discussed this concern has ever expressed confidence in such a band-aid approach.

I don't spray nor even try to re-line buried HVAC ducts, I find an alternative duct routing solution or in a few cases we change to hot / cold water piping above ground.

We cannot know that the entire duct interior has been coated and sealed adequately, we cannot know that it adhered everywhere, and we cannot be confident that in the future some "sealer" section does not collapse or fall away from water, water pressure, soiling and contamination, or another failure that in turn leaves the occupants thinking the problem was solved when it was not.

Can't I just siphon water out of the ductwork and then run the blower to dry them out?

Before replacing ducts why not siphon water out of duct then run a/c unit on. On 2017-09-14 by Anonymous

Reply by (mod) - cannot dry out wet insulation in HVAC ducts thoroughly nor quickly enough to avoid mold

Great question, Anon.

The problem is that most-likely you cannot dry out wet insulation in HVAC ducts thoroughly nor quickly enough to avoid mold or other contamination such as bacterial growth if ductwork has been flooded.

You would need to remove all ice, water, condensate, humidity down to a safe level, say 15%, in about 24 hours or at the most 48 hours after duct insulation has been wet.

The concerns are

1. Too little, too late: he system will not remove enough water and moisture quickly-enough

2. Incomplete dryout leaves serious trouble: there is just no way to know, nor assume that even if some duct inside areas are "dry" there are not other elbows, corners, bends, connections that remain wet and become a mold hazard, worse, a clandestine one that troubles building occupants who think that the entire duct system is clean.

Similarly, sanitizing procedures generally won't address flooded ductwork problems.

A plumbing leak wet our in-floor ductwork. Insurance didn't cover duct replacement. Now I see trouble.

We had a flood in 2011 caused by sink valve leak. Got home and all house flooded a few inches with water in in floor heating ducts (we have a slab).

Insurance covered remediation of home but nothing ever replaced w air ducts or register boxes. Now I see rust spots opening to gravel below house. Heating co cant replace register boxes w/o a mason digging up floor for all registers. We can get a new upflow furnace and new ceiling vents but this will get expensive. Suggestions? On 2017-03-22 by Ruthie

Reply by (mod) - water in in floor heating ducts (we have a slab).

It sounds as if the home remediation may be incomplete as flooded -in-slab ducts are likely to be a mold or pathogen reservoir;

You don't have to dig up in slab ducts to abandon them. Search InspectApedia.com using the box just above, to find SLAB DUCTWORK to see a series of articles discussing the problem and various solutions. Yes none are cheap.

Washing machine drain flooded flex duct: Should I replace the ductwork?

My washer hose became disconnected and water went down an air vent and into my flex duct. Cut the duck work the next day and drained water. Should I replace or what should I do? On 2016-07-21 by Sheila

Reply by (mod) - replace any flex duct if its insulation got wet.

I would replace any flex duct if its insulation got wet. The risk of waiting is having to do a still more-expensive mold remediation job of the whole HVAC system including the air handler itself later on, or even mold related illness in building occupants.

I Fixed Condensation Problems in my HVAC Ducts, but Now I Have Metal Chimney Condensation To Cure

First I must thank you for your article on condensation in conditioner ducts that are in the attic and not used for heating

- see details at WATER & ICE IN DUCT WORK

I had the same problem as in your article and had several AC techs and a P.E. look at the problem and not one of them could come up with answer.

Since I blocked the return and register grills the problem disappeared. Perhaps you could suggest an answer to another problem.

I have a gas boiler and a separate gas hot water heater in the basement. I have a metal chimney into which they are connected. The chimney goes up through the roof. The chimney extends about three feet below where the boiler flue and gas flue are connected.

I am getting condensation dripping out of the bottom of the chimney pipe - there is not a large amount and it appears to be coming down the inside of the chimney and then leaking out. Any suggestions? Thank you for your help. F. D. - Mattituck NY

Reply: Check These Chimney Safety Worries First

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem. That said, here are some things to consider:

• You will want to be sure to distinguish between a water or rain leak into the flue - a problem you'd fix by fixing a chimney cap or flashing - and a chimney leak due to condensation (occurs where there's no rain nor melting snow)
• If it's condensation there is either a chimney problem (too cold, wrong flue size) or an equipment operating problem (insufficient combustion air or draft or a similar problem) - details are
  
  at CHIMNEY WET TIME & CORROSION

Watch out: I'm afraid that those conditions are likely to be unsafe and could include a carbon monoxide hazard - so be sure you've got working CO detectors.

 

Question: should I see water in the overflow pan under my attic heat pump air handler?

I have a dual heat pump setup, is it normal for the attic heat pump air condition over flow pan under unit to keep water in it. (July 22, 2014) Joe

Reply: no, that means there's a drain problem to fix asap

Joe if the overflow pan has water in it then there's a problem to find and fix.

Either the main condensate drain is not draining
or

water is entering the condensate overflow pan when it should be going into the main drain pan
or

there is a leak in the air handler drain pan

...

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Continue reading at WATER & ICE IN DUCT WORK or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BLOWER LEAKS, RUST & MOLD
• FROST BUILD-UP on AIR CONDITIONER COILS
• FLOOD DAMAGE REPAIR PRIORITIES
• HEATING EQUIPMENT, FLOOD DAMAGE REPAIR
• WATER & ICE IN DUCT WORK - topic home
• WET CORRODED DUCT WORK

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC DUCT SYSTEMS

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