Home Healthy Home Reader Q & A: Air Quality Issues With In-Slab HVAC Ducts and Knowing When It’s Time to Call a Professional for Help

Reader Q & A: Air Quality Issues With In-Slab HVAC Ducts and Knowing When It’s Time to Call a Professional for Help

by Catherine

This week, I am going to devote time to answering and sharing a recent mold/indoor air quality issue question that came my way. It concerns a very specific way of installing HVAC ductwork, where the HVAC ducts have been placed in or below the concrete floor slab. To better illustrate this to you, I asked a contractor to describe the installation process to me. Here is what he said:

“As the home is being built, trenches are dug in the soil before the concrete foundation is poured. Wooden or concrete blocks are then placed in the trenches and the HVAC ducts are pieced together and placed in the trenches on top of the blocks according to the home’s layout and the HVAC blueprint. Many times, the ducts are in direct contact with the soil. Concrete is then poured around the ducts as they lay in the trenches. Finally, the concrete slab is poured on top of the ducts/trenches to form the home’s foundation.”

This practice of in-slab ducting has become notorious for different types of problems, like functional troubles (lack of air flow or collapsed ductwork), and environmental problems (radon, odors, flooding, mold, insects). The main reason I want to address this question on the blog is because of the many indoor air quality issues inherent in this type of construction that I think people need to be made aware of. I also think this question is an important one, because it involves all of the components of needing to be a “mold detective” and a health advocate for yourself. This is because watching out for potential health hazards in your home and other frequent indoor environments can protect you from long-term health consequences. In other words, if it smells like mold, you can see it, and/or your body feels “off” in a particular environment and like something is making you sick, chances are that your body is right, and it is mold or something environmental. Thus, you have nothing to lose by taking steps to safeguard your health by investigating and fixing your environment as soon as something seems amiss.

So, let’s begin. Here is the question that sparked this post:

(Note: I value all of you and the fact that you trust me enough to reach out to me with your questions. In an effort to keep all conversations private, I am not going to share the reader’s name or specifics, just the general question or issues that the reader had. Some of the wording in the question has been changed to protect identity.)

Hi, Catherine,

I was wondering if you had any recommendations or could provide guidance. My family and I came home after a week vacation and after running the air conditioning began having allergy symptoms, for example itchy eyes, runny nose. I replaced our HVAC filters. That seemed to help, but we still seem to get the itchy eyes on occasion. Also, before we left on our trip and still now, we notice a distinct but not obvious odor that seems to be coming from a couple of our kitchen vents. Our downstairs system duct work is unique. The air travels from the attic blower down one large supply line to our cement foundation/slab. From there (inside the slab) our supply ducts spread throughout the home to various rooms. I would like to have someone look through our supply ducts via camera (to see what, if anything is going on or inside of them) and possibly clean them. What kinds of companies would you look for to do this work or that you would trust to assess this type of issue? Do you have any recommendations that I can do myself with products or “cleaning for mold” if we find that it is growing inside the ducts? I know that you advocate the AprilAire whole-home air purifiers, but is there alternative? None of my family has any of these same health symptoms or issues when we travel to various hotels or houses. Thanks so much! I “liked” your FB page and have perused your website. Lots of great info there! I am impressed.

Here is my response:

(Note: Remember, I’m not a professional by any means. I just have my personal mold experience and recovery, and a few years of writing this blog and interviewing “building science” professionals and doctors in the field of environmental medicine and mold illness to base my responses on. This is all just advice and not a diagnosis or professional recommendation. Please, take it as such.)


After reading and re-reading your message, I have a few insights for you:

First, I think your symptoms are most definitely environmental and are most definitely related to the environment and air quality inside of your home. One of the telltale signs of environmentally-triggered illness is feeling noticeably better away from your home, and then having a return of symptoms when you come back.


Second, and I hate to be the bearer of bad news, but duct work laid in the slab is notorious for flooding, collapse, rodent intrusion, mold, sewer gas seeping in, and radon gas. The problems with routing ducts into the slab have now made the practice in residential construction pretty taboo. I would say that if you can solve this problem, your air quality issues will be SIGNIFICANTLY improved, if not solved. You cannot just clean the ducts, though, and be done with it. If there is a smell, and you are experiencing allergy symptoms, it is highly likely that there is something in or going wrong with the in-slab ductwork.

To get professional insight and a “trained” look at the issue, I would advise seeking an environmental or Indoor Air Quality-certified professional (IAQ pro) to feed a camera through the ductwork to see what is going on. This person can also test for radon, sewer gases, and possible mold and bacterial growth, although, the mold is usually visible on the camera, if it is actively growing inside the ducts. More systemic mold issues throughout your HVAC system and health issues from the damp/moist ducts could exist. Scoping the ducts will also let you know if you have rodent intrusion or a nest down there. For obvious reasons, if rodents or dead rodents are in your air supply, your health could be impacted negatively, and the problem will need to be eradicated. A trained professional should also know that if there is any visible rust, the ducts or the slab were not properly sealed, and there has been water intrusion or flooding in the ducts at some point, thus the rust.


In addition, the camera view will show structurally if the ducts have collapsed, which happens often with that type of routing. Deteriorated ducts effect the quality of air inside the home, because air flow and ventilation are obstructed and the failing materials can become tiny particles that enter your indoor air and make you sick. Permeable soils underneath rotted/deteriorated ducts allow mice and other rodents and insects to enter. This can also cause respiratory-related health risks. And, depending on if the ducts are metal or wood/paper products, such as Sonotube, termites could be present. There is also the danger of radon gas entry.


All of this important to figure as soon as possible, not only because it could be affecting your health, but also because bad ducts located beneath the slab could and often effect a real estate transaction in the future. Thus, the earlier you can take care of it and fix it, the better.


Once your ducts have been inspected and you know what you are dealing with, you can fix the issue, either by sealing the slab better and replacing the contaminated or failed ductwork (not my first recommendation, but an option), then fogging or cleaning the entire system with a non-toxic product, like EC3 Mold Solution Concentrate. If there is any mold found in the system, you will also need to have your HVAC coils and plenum cleaned with an antimicrobial, antifungal and sanitizing product, like EC3 Mold Concentrate. A professional should do this so as not to damage the unit or cause corrosion, because, if mold is in the ducts, then it is everywhere in the system and must be taken care of. Make certain that the product being used to do this is not toxic, because it will be distributed in the air throughout your home and can cause health problems in its own right if it is full of harmful chemicals.


The other “fix” option (and the better one in my opinion and experience) is rerouting the HVAC system and/or installing a split system to bypass the old route and reroute the supply ducts somewhere else. Most of the time, you’ll have to seal and cover or floor over the floor supplies to the old ducts, though.  This sort of work can balloon into a remodel project and become costly, so it is an option that some people just cannot afford to choose.


I know, this is tons of info, but I just wanted to tell you everything I know–which is just scratching the surface. I am only an “armchair/blog expert,” if you know what I mean. To find the right kind of professional to help you, you should look specifically for Indoor Air Quality experts, Indoor Environmental Inspectors, or certified Bau Biologists (those trained in the science of indoor air quality and building health and biology) in your area. You can use sites like IAQA.org, The National Organization of Remediators and Mold Inspectors site (make sure to search for those certified in IAQ), and The International Institute for Building-Biology and Ecology. These experts understand the building physics, the chemistry or biology of the contaminant, and the physical impact on human health.


I used a company from out of town on our home, because no one who dealt with mold and understood the health repercussions of mold existed in my city. If this is the case for you, I would look in surrounding cities too, because professionals in this industry do travel. You don’t want any regular or less experienced HVAC company or general contractor doing the inspection work in my opinion, because they are not a neutral party. Their inspection will be biased towards finding things to make more money off of the work they can do to fix it. In general, the cost of an indoor air quality inspection and review is usually around $400-$500 for the complete house. This does not include specific mold testing, air testing, and/or samples sent to a lab, though. If you only want them to inspect the ducts and HVAC and offer recommendations on that, I am sure the price can be negotiated. I do think it is smart to go ahead and allow them to do a full inspection and review of your home with recommendations while they are already there, though, because they may find things that you could fix or make better now or in the future that could have a big impact on the health of your home. It was my experience that the information gleaned from our report has been invaluable to doing home improvements little by little to make our home even healthier over the years. For example, we just built an awning over our back door to prevent possible water intrusion during hard rains. We didn’t do it right away when the recommendation was made, but just completed it as both an aesthetic addition to our patio and a mold avoidance measure.


To answer your question about the AprilAire purification system, that doesn’t need to be a consideration until the problem is fixed. Not even the best filter and system can solve a mold problem in the ductwork. They are designed to help keep mold and allergen counts down in the air and to prevent them from getting high enough to cause health problems in a home that does not have known mold issues.


Anyway, I hope my reply doesn’t make you run away from home. I also hope that I have helped. In the meantime, while you absorb and process this info, here are a few low-cost things you can do immediately to help your symptoms and to maintain your health if your environment is less than ideal air-quality-wise:


1) Burn EC3 Air Purification Candles in the rooms where you spend the most time. Use the candles per package instructions. They will purify the air and eliminate mold spores and mycotoxins and help you to feel better. They need to continuously burn, though, if possible.


2) Use a saline nasal rinse, like Nasopure 2 times per day to flush all dust , allergens, and any mucous from your nose. Help your children do a saline rinse as well. Everyone needs their own bottle. If you are helping your children with theirs, I have mine lean over the tub and I put one side in one nostril and gently squeeze the water in until it runs out the other side. Then, I repeat on the other nostril. Never create a seal with the bottle, though, because you could hurt their ears. You can also add CitriDrops Dietary Supplement to the rinse. I would only put about 2-3 drops in a full bottle of saline. This has antifungal and antimicrobial properties that will help to get rid of anything trying to take up residence in the warm, moist environment in your nose.


3) In addition to the saline rinse, use CitriDrops Nasal Sprays, both you and your children. For you, squirt each nostril 4 times at least 3 times per day. For your children, do 2 sprays in each nostril 3 times per day. Again, everyone needs their own bottle. This will eliminate any fungus, bacteria, allergens that are in the nasal passages. (Most mold enters the body through the nose. This stops it from creating the allergic response.)


4) Use Sinus Defense to create some natural antibodies to the mold and indoor allergens. For you, I would use 6 sublingual sprays 3 times per day. For the kids, use 3 sublingual sprays 2-3 times per day. This stuff is awesome and works if you are consistent. It contains colostrum that targets mold antigens and other mold-illness-related allergens and viruses. Using colostrum leverages your body’s natural T-cell immune defenses.  It also works quickly, within days. Your resistance to mold will increase and your body will be more resilient to it, which is what you need, since you are living in an environment that seems to be causing you problems.


That’s all I’ve got! Let me know if you have any questions or concerns about any of my advice. Good luck and let me know how it goes.

I hope this Q & A was helpful for YOU too. Do you have any questions for me? Is there an air quality or cleaning for mold situation in your home that you want advice on? Write to me at catherine@moldfreeliving.com. Maybe I can feature your question on the blog next.
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