Q&A / 

Air Duct Cleaning and Sealing

DEAR TIM: I just discovered that the air ducts in my concrete slab have problems. There was an odor that alerted me to the issue that there was standing water, debris and even a dead animal in the ducts below my floor. It was disgusting. I have galvanized air ducts installed when the house was built. I got a bid to have these abandoned and rerouted through soffits or the attic of my home. Are there other options? Can I get my air ducts cleaned and possibly sealed so there is no future problem? Mandy S., Laguna Beach, CA

DEAR MANDY: Oh, I’m so sorry to hear about this. There are tens of thousands of people who have galvanized thin metal ducting buried under the concrete slabs of their homes just like you. The piping can corrode in very short order. What’s more, rarely were the joints between two pieces of pipe or fittings ever sealed to prevent the infiltration of ground water. What a mess!

The good news is that an alternative method to clean and seal air ducts exists. Yes, it’s possible to abandon the under-slab ducts, but putting them in soffits or an attic might be problematic for certain homes. It can sometimes be so expensive that it would take your breath away. There are several different ducting systems that may work and not be horribly expensive, but there will be dust and disruption in your home.

But before you make a decision, be sure you get a quote from a company that can use your existing ducts and not have workers creating clouds of dust. I know of a modern system where you can begin to use your furnace or air conditioner as the workers leave the driveway. You can’t always do that if you’re going to install new ducting in an attic, and most definitely not if you decide to hide new ductwork in soffits in each room.

Perhaps the least disruptive, and often the most affordable, method to solve your problem is to have the interior of the existing buried ducts cleaned and sealed with a non-toxic latex plastic.


Here is the first of two photos. In this before image, you can clearly see that it pays to have ducts cleaned and sealed if you have problems with air flow, odors or water in the ducts.<br /><p class=PHOTO CREDIT: Enviro Duct Seal Technologies" src="http://media.askbuild.com/legacy/889-01.jpg" width="350" height="263" /> Here is the first of two photos. In this before image, you can clearly see that it pays to have ducts cleaned and sealed if you have problems with air flow, odors or water in the ducts.
PHOTO CREDIT: Enviro Duct Seal Technologies

The first step these innovative companies take is to film a video of your buried ducts. That way they can show you the exact issues. There is always a charge for this service, but if you decide to use the company to solve the problem, you get the fee credited to the final price of the job.

Taping this video allows the contractor to see all of the problems and give a professional assessment of the situation. You get to watch the video yourself, and if you’re home while it’s being taped, can watch it live on a monitor!

Once it’s determined the process will be successful in your home, the ducts must be professionally cleaned. This is also easy to do, and it often requires that your furnace or air handler be temporarily removed so the workers have complete access to the main trunk lines and all the branch runs of the ducting system.

After the ducts are cleaned, the duct sealing company comes back. They have a special airless spray system equipped with a live camera that navigates through the labyrinth of ducts beneath your slab. This allows the workers to see that the duct is being coated properly with the proprietary latex compound. This sprayer makes its way through each duct and seals as it moves.

In this after photo, you can clearly see how the ducts have been cleaned and sealed.<br /><p class=PHOTO CREDIT: Enviro Duct Seal Technologies" src="http://media.askbuild.com/legacy/889-02.jpg" width="350" height="262" /> In this after photo, you can clearly see how the ducts have been cleaned and sealed.
PHOTO CREDIT: Enviro Duct Seal Technologies

This spray compound is similar in nature to a very thick latex paint and starts to dry immediately. You can use your air conditioner or furnace within hours after the ducts are sealed. A second coat is applied after the first coat is dried and cured.

If I had buried ducts like you, I’d definitely consider this method. I’m attracted to it because of it’s technology and the fact that there is no disruption inside the home. I also like the fact that it comes with a strong 15-year warranty in most situations.

What’s also attractive is the plastic liner, along with a special hydraulic water-stop material used at the metal register boxes and the plenum, help make the ducts highly water resistant. Realize that the inside of the ducts, once the system is cured, is lined with a continuous uninterrupted layer of thick plastic. After the latex compound cures, water has a very tough time entering the ducts. If water does enter, the lining system makes it easy to vacuum out.

As with all jobs like this, it really pays to get multiple opinions. You want to be sure that the process works, and will work flawlessly for years.

One of the things I would absolutely do before signing a contract would be to call past customers who had this magical compound sprayed on their ducts. You want to talk to customers who’ve had it done from three different time periods: the past 60 days, a year ago, and possibly back as far as three years ago.

Perhaps the most important question to ask the homeowner who’s had his ducts cleaned and sealed three years ago is: Has the process delivered on all it’s promises and would you hire this company again?

The homeowner that’s had it in for just a year would be able to tell you how their after-the-sale service is. Sometimes there are minor issues. What you want to ask them is: Did the company come back and take care of the warranty issue with no problems?

Finally, the most recent homeowner would know how professional the current employees are. Ask them if they would invite the workers that cleaned and sealed the ducts to a picnic in their backyard. If they say Yes, then you probably have a great company at your disposal!

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