Water and rodents in air duct (C) D FriedmanIn-Slab Heating or Cooling Duct FAQs
Diagnotic Questions & Answers for HV AC Ducts Routed in Floor Slabs

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HVAC ductwork in floor slabs: diagnosis & repair or abandonment FAQs.

Questions & answers about how to diagnose, repair, or abandon under-slab or in-slab heating or air conditioning ductwork.

This article series describes heating and air conditioning ducts that have been placed in or beneath concrete floor slabs.

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FAQs about Abandoning or Troubleshooting & Fixing HVAC air ducts in concrete floor slabs

These questions & answers about diagnosing & fixing problems traced to in-slab air ducts were posted originally at SLAB DUCTWORK - topic home.

On 2017-07-23 by (mod) - troubleshooting high indoor moisture possibly due to in-slab ducts: vines in the ducts?


In many in-slab duct systems, over the life of the building, ducts leak somewhere. I would if necessary hire a plumber who has a sufficiently-long sewer camera system - some duct companies also have these - to inspect the whole system.

Rust may be from
- water entry from below or outside the building
- condensation (ducts in cool slab not insulated)
- leaks or floods in the building that leaked into the duct system

Where you see gaps but no obvious leaks it may be that the ducts are surrounded by concrete and no dirt or vines or rodents are entering there.

But where you find vines in an in-slab duct you can be certain that at times water is or has also in the ductwork. I would abandon such ductwork.

IN general if you are seeing a lot of indoor moisture and you become confident it's not a duct in slab problem, we need to go looking for another moisture source.


On 2017-07-23 by Scott

Thanks for your quick reply. During home inspection, they looked in a couple of the ducts and didn't find problems past the boots. However, I recently bought a borescope and decided this should be the day to look myself.

My flex rod is only about 15 feet long so I can only push the camera in about 15 feet. I looked into every duct. Some seemed ok except the normal settlement and dust debris. A few however had some definite rust spots where obvious water had been.

One even has vines inside it. The vines don't appear to be actively growing, but they obviously came through a hole in the duct and had been active for a while. There are a couple poorly constructed joints where I can see major gaps (1/2 - 1") between the metal material. I don't see rust or dirt in the gaps though.

No standing water though. I have a bit of a hard time believing the gaps are where my humidity issues are coming though. The ground here is bone dry as it hasn't rained in 2months and there's no obvious point of active water entry.

Regardless, I'm going to have a duct company come out and give me a better inspection and estimate. As for the HVAC system, both of the companies I had out said my system was sized correctly.

I would have thought at least one of them would be interested in selling me something if it were an obvious solution. I don't think duct work along the exterior of the house is a good idea, as this house will never sell if I ever choose to do so. Too many questions from potential buyers, I'd think. That means I can't seal the ducts in. I need to find a solution with what i have.

Thanks again for your feedback and thoughts. I'm sure there are other solutions that I've not even considered.

On 2017-07-22 by (mod) use a remote camera to inspect in-slab ducts for water, breaks, rodents, mold

If you have not had all of the in slab ducts in the specs for signs of leaks or periodic water entry I would do that.

A remote camera works perfectly for that job. If the ends lab ducts are seem to be absolutely dry then I would look next at the size of your air conditioning system to be sure that it is correct since a two large cooling system will not dehumidifier. Tell me what you find with those two steps and then we can proceed further.

On 2017-07-22 17:53:25.844607 by Scott: tracing high indoor moisture to slab ductwork

Thank you for this great article. I'm trying to figure out my homes problems and decide on a course of action. I'm in a two story house. My problem is very high humidity. I have two dehumidifiers running, pulling out about 4 gallons of water every day. This only happens in the summer. The house is about 1800 sq ft downstairs and additional 1800 upstairs. The upstairs has nice crisp, cool air.

The downstairs has cool, but moist air and often feels like a sauna, despite the air temp being cool. The lower level has in-slab ducts with a single air return. I have increased the size of the return, as multiple HVAC contractors said it was too small for the size of the space. They also all confirmed that my HVAC unit is sized correctly for the size of the space. I do not see signs of duct failure, though during our inspection, the register boots were corroded or rusty.

We had them install new boots prior to closing. A separate issue with the house is that I've discovered the Sheetrock that was installed between the exterior siding and the 2x4's had cracked and been removed near the bottom of the structure.

It appears the previous owners just nailed the siding into the 2x4's to remove the gap that was left. I'm concerned that has created inadequate insulation so now we have humidity being sucked in through the exterior walls. Basically, no vapor barrier.

What is more likely causing my issues? Wall insulation or in-slab ducts? I can't afford to do everything so need to pick most likely culprit. Thanks for the feedback.

On 2017-02-15 by (mod) - meaning of standing water in ductwork


Standing water in in-slab ducts now or in the past would tell me

1. I'm going to abandon use of that duct system, as it invites mold, other pathogens in my indoor air, improper heating and cooling operation, maybe even unsafe operation. Abandoning usually means filling-in as much as possible, sealing openings into the building, and installing an alternative heat distribution system - above-ground ducts or as was done in my house, conversion to forced hot water heat.

2. There are leaks or water sources (perhaps roof drainage) sending water under the slab, asking for an indoor moisture, water, or mold problem that need to be diagnosed and fixed

3. an alternative duct system is needed, above the slab.

On 2017-02-13 by MG

Hello! Thank you for all the useful information so far! We purchased a 1968 house in which the heat/cool supply runs through the slab. Upon moving in, we noticed standing water in the the ducts. At that point, we installed an interior french drain and sump pump.

I don't believe we have had any standing water (at least noticeable) since the french drain installation, now at 6 years. A couple years back, we hired a duct cleaning service to clean as I noticed the vents appeared dirty (rusty and full of bugs).

The duct cleaning company said they could not clean our ducts because they believed them to be asbestos lined. Fast forward, we are currently remodeling and think it is a good time to address the duct situation.

Do you believe that we should first line the ducts with protective coating and then fill with concrete? Or do you think we should just fill with concrete to abandon? As you know, this is a costly problem which also includes re-routing several supply lines for heat to the basement areas. Thank you, M.G.

On 2017-01-18 by (mod) recent research on HVAC ductwork in slabs focusing on Canadian buildings or Canadian research

In the 1940's and 1950's even into the 60's it was common to build homes with HVAC ducts in slabs in North America, including both the U.S. and Canada.

I haven't found a census of slab ductwork in Canada, but by 2000 many of those older in-slab duct systems (in both countries) had been abandoned, largely because of the problems discussed in this article series. But new in-slab duct designs are still being built as you'll read in the research I cite below:

Here is some more recent research on HVAC ductwork in slabs focusing on Canadian buildings or Canadian research

On 2017-01-18 by MP How common is in slab ductwork in Canada?

How common is in slab ductwork in Canada?

On 2017-01-09 by (mod) - covering openings in slabs


If the opening you describe is the system's return air, closing it off will cause your heating system to work at about half of its capacity or less and at double its operating cost or more. You'd need to provide an alternative source of return air.

On 2016-12-16 16:52:48.292215 by I have a an opening in my slab. my umit sits on top of it can i cover it

Have an opening in my slab. Unit sits on top.
Can I cover it? Cold air coming up

On 2016-11-20 by Anonymous

Thank you for your response. I appreciate your insights.

I didn't know that it was possible to convert a down spouted furnace to a side or up. I was told by a tech that it would need to be replaced, but I guess that is not the case.

The spray was something I thought would be the cheaper way to go. If you have a home owner looking to sell. They more then likely will want to take the cheaper route :)

Thanks again & have a good night

On 2016-11-19 by (mod) Does the insurance companies cover any remediation costs for sealing up the vents and relocating them to another area? attic or walls ?


OPINION: I would doubt if many insurance companies will cover the cost of any building "repair" that is essentially correcting an original design, nor do most policies cover the cost to repair problems traced to wear and tear, lack of maintenance, nor in many cases leaks.

I agree that the cost to both close off in-slab ductwork and to provide alternative heat can be very costly. But while I in-slab ducts are a common problem source, it would not be correct to assume that every home with in-slab ductwork has a serious problem that needs to be addressed.

It would be reasonable for a home inspector to inform a buyer or owner (whoever has hired the inspector, usually the buyer) that in-slab ducts present certain risks of air quality and health concerns, particularly if there has been water or flooding into the in-slab ducts OR if the area where the home is built is known to often have actionable levels of radon. In such cases it would make sense to plan to do a bit of exploring in the duct system, inspecting for evidence of collapse, flooding, or if appropriate, radon testing.

Some ducts that are in good condition and are below grade are re-sealed (using a spray) in place and continue in use, but I'm nervous about that approach as I'm not confident there won't be a future water and contamination problem. You wouldn't want to be the one "guaranteeing" that such a job will be in the future trouble-free.

I am not sure that it's appropriate either to assume that a new furnace is needed just because of in-slab ducts. If the up-flow furnace is relatively new and in good condition I'd probably consider modifying it to work with new in-wall above-slab ducts on the return side.

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On 2016-11-19 by JodiAnn

Hello, I have been reading through all your information and recommendations and have found it very helpful

However,I have a couple of additional questions. As a realtor in Monmouth County NJ I am often asked about this and to be honest I am afraid to answer. I don't want to open myself to being suited by a past client. So here are my questions

Does the insurance companies cover any remediation costs for sealing up the vents and relocating them to another area? attic or walls

This is quite costly. Most of the time it requires additional work to be done not just filling the slab with concrete.

A new furnace with an up-spout. Running all the ducks and possibile replacement of the AC. It can cost thousands of dollars so I've been told. $15,000 to $25,000 as an estimate is this true?

Most importantly does homeowners insurance cover this? ANy type of rider that can be added if needed?

I have also heard of a possible solution called Areo seal. Where they claim to spray a sealant into the ducks designed to prevent water coming in.

There are many homes in the area where I live with this type of duck work. I'd really like to be able to help make suggestions?

Any help or answer are greatly appreciated

On 2015-11-07 by (mod) - are some HVAC systems noisier than others?

Yes some HVAC systems are normally-noisier than others.

See SOUND CONTROL for AIR DUCTS, HVAC as a place to start;

Also see


On 2015-11-07 by Dave

Our furnace seems louder than our a/c unit. The hvac system is really close to our family room and seems really loud at times. Is there some systems that are quieter than others? Or is there any way sound proofing the closet?

On 2015-10-20 by (mod) seal the vents with foam and concrete the top portion

Denny that can in my OPINION be a reasonable approach to duct slab abandonment; I've done something similar. The risk is that water and pathogens collect in the un-filled under-slab duct sections.

My view is that IF there are no cracks, holes, pipe or wire penetrations or other openings that would allow contaminants to pass through the slab surface into the building, then sealing at the registers may be adequate. Your final "top portion" seal needs to be fail-safe.

On 2015-10-19 by Denny

I'm about to enclose slab routed ductwork in a commercial site. My thought was to seal the vents with foam and concrete the top portion. What do you feel about that.

On 2015-09-16 by Anonymous

Joey, you'll want to call 3 contractors in your area to ask for bids on the new HVAC work and you may need to find a separate masonry contractor to pump the appropriate mix into and thus fill and seal the slab cucts.

On 2015-09-16 by Joeyz

Ok. I have the problem and want to get rid of it. I have a 1377 sf ranch on a slab. Can anyone give me a ballpark estimate on How much it would cost and who to call? I want to seal off everything, run ductwork into attic where I will need to have it insulated and buy a new furnace and ac unit.

Question: so much debris from our ducts & it's making us sick

Dec 5, 2012) TA said:

HELP! so much debris from our ducts & it's making us sick; burning eyes, nose, throats & when it comes in contact with our skin it burns which is hard because it is everywhere.

The debris is significant the dust is covering everything in the condo some days its 1/4 inch thick from floor then onto everything up to the ceilings. Our family is getting very sick & neighbors in their units are getting sick too.

We were told we could even get silica poisioning. The association claims it's not their problem; how do we fix these serious & life altering issues. We heard some of our neighbors that have been complaining about the dust actually died from lung cancer & never smoked other cancers too. We've also had raw sewage leaks into some of the duct work.

They refuse to fix it correctly. We are still walking on steam cleaned kah-kah ffrom the 2 raw sewage episodes. PLEASE HELP US our child is having sever health issues & docs are telling us to see toxicologists. How do we fix this? Built in 1985 with beer cans in the attics & duct work & we are ill & annoyed in ILLinois


(Jan 24, 2013) ls said:

If you abandon the ductwork and forced air system of heating, what is an efficent and affordable way to heat your home?

Question: is HVAC duct sealant silicone free?

(Feb 14, 2013) Anonymous said:

Is this sealant is oil and silicon free


Not necessarily; check the MSDS for the sealant that you are considering, or tell us the brand and product identification and we'll help research that data.

Question: could my deteriorated in-slab ductwork be contributing to indoor condensation?

(Feb 28, 2014) Incognito said:

I know the in-slab ductwork in my house has detiorated. Could this also be causing the severe condensation problems I'm having on the inside of my windows and on some of the walls? This only happens in the winter.


Yes Incog. If there is water in the slab ductwork that moisture may be transported into the rest of the building.


(Mar 9, 2014) John said:

Hi Dan,
Great article because I'm worried.

I have 2 registers in my living room Ohio home. One works fine (had furnace recently checked out ok) and the other has no air coming out. The orange clay pipe duct collapsed and what is strange is there is no duct symbol on the design print where that register is located.

Anyways, the living room has heated up fine for me for 20yrs. Ive just always kept the register closed. There is no water inside the register duct, only what looks like tons of pea gravel underneath that I can fell with my hand reaching into the duct and remnants of the broken clay pipe duct.

My question is can I just legally close of this registerduct by filling with concrete or leave it as is? I want to sell my home this Spring and my conscience won't allow me not to disclose this on my property disclosure form, but I'm worried that this will make it hard to sell my home or impact the price greatly. I cant afford to put new heating system in and run all new ducts in the attic.
Help (wish I could talk to you).
thank you, John

Other details:
My house is on a slab.
The clay pipe ducting is in or under the slab.
Built in 1971


Opinion: I would fill in the abandoned duct with concrete. The code or sale issue would perhaps turn on adequacy of heat delivered to the space. If you have other supplynregister(s) into the area that may suffice. If there is no active heat source into that room you may run into an appraisal or code compliance issue. If there is a supply,duct into a room on a opposing wall that might be extended to the unseated room as well.


Thanku Dan,

I plan to fill the register vent/duct with pea gravel and top with concrete at buyers request and get a local certified hvac techs approval. There is a 2nd register vent in the living room that works fine (95+F air).

thank you sir


Thanks for the clarification John; having a second working register in the same room may get past the "no heat source" concern at appraisal time. Niether home appraisers nor home inspectors will normally perform a heat loss calculation nor heating adequacy assessment unless there is a visually apparent defect.

Question: rusty cement smell in the cooling system

(Mar 10, 2014) Wendy said:

I can smell musty cement in the evaporative cooling system in the unit I have just rented. Should I be concerned about this ?


Wendy, the system may need to be cleaned; I don't know what you're smelling, but as an evaporative cooler cools by blowing air across water, if the water source is contaminated with bacteria it could be unhealthy.


(June 6, 2014) Anonymous said:

Thanks for this informative article. We are considering purchasing a house (split ranch) with duct under concrete in the lower level of house. I am guessing we can pour concrete to the ducts, close the vents and lay new ducts through the walls . Is this a realistic approach ? Any idea how much cost we are looking at ?


10/10/2014 Bryan said:

My home is approximately 6 years old and about 1 year ago I noticed noise coming from the under slab register openings as when heat/cooling system was blowing. I exposed the air supply and register vents and found standing water. The builder used what appears to be flexible stainless conduit under the approximately 45ft span from mechanical room to below windows (2) on far side of family room wall. The room is a walkout basement room with open section to the main levels of the house for full air circulation.

Upon inspection again today I noted same problems following heavy rains and noted what could be mold and algae. The conduit was pumped as much as possible and it is noted that holes near the air supply end exist in one line. Digital pics taken from each end show crushing of the line and obvious signs that water had been in line for substantial periods. What are my best options for the situation. I currently have sealed the line with foil insulation wrap and plugged air supply lines on main duct.


I'd like to see your photos of the slab duct conditions - use the email found at our CONTACT link (seen at page top or bottom).

Because the leaks into sub-slab ducts are and have been recurrent and are likely to recur, the best approach is to abandon and fill in those ducts and reroute the ductwork. In some houses where the cost of rerouting ducts is heinous owners opt for adding alternative heat, even a few electric baseboards.

Question: noise from ducts under the slab - water, collapse: what are my options?

(Oct 9, 2014) Bryan said:

My home is approximately 6 years old and about 1 year ago I noticed noise coming from the under slab register openings as when heat/cooling system was blowing. I exposed the air supply and register vents and found standing water.

The builder used what appears to be flexible stainless conduit under the approximately 45ft span from mechanical room to below windows (2) on far side of family room wall. The room is a walkout basement room with open section to the main levels of the house for full air circulation.

Upon inspection again today I noted same problems following heavy rains and noted what could be mold and algae. The conduit was pumped as much as possible and it is noted that holes near the air supply end exist in one line. Digital pics taken from each end show crushing of the line and obvious signs that water had been in line for substantial periods.

What are my best options for the situation. I currently have sealed the line with foil insulation wrap and plugged air supply lines on main duct.



I'd like to see your photos of the slab duct conditions - use the email found at our CONTACT link (seen at page top or bottom).

Because the leaks into sub-slab ducts are and have been recurrent and are likely to recur, the best approach is to abandon and fill in those ducts and reroute the ductwork.

In some houses where the cost of rerouting ducts is heinous owners opt for adding alternative heat, even a few electric baseboards.

Question: high radon levels in house with ductwork in the slab

(Nov 1, 2014) Sam said:
I have a 3 level house. Level 1 and 2 have slab floors. Level 3 is above level 1 and has wood floors. A sub floor set of ducts carries hot or cool air through the house from two furnaces located on level 1.
The house has a high radon reading. The radon cycles daily with lower readings in the day time and highest readings at around 1 am at night.

I installed a radon mitigation system on level 1 but was told thats its effectiveness could not be guarenteed becasue of the presences of in slab ducting.
I want to resolve the radon issue.

After reading a lot I felt it would be reasonable to consider the following as mitigation.

1 isolate the inslad system system from the ducts that connect to level 3 with wooden floors
2 seal the exits of all the in slab ducts
3 Find a way to put negetive pressure on the in floor ducts snd exhaust

I thought I would replace the current 2 zone ducted system with heat pump cooling and heating. Each room having its own unit allowing individual control
2 find a way to apply suction to the remaining ins



Rather than the cost and trouble of trying to establish negative air pressure in the in-floor or in-slab ducts - which is impossible if the ducts are being used to supply conditioned air to parts of the building - a more effective approach is to abandon the in-floor ducts by filling them with concrete (best) or filling and sealing at least the ducts at and around each supply and return register using concrete.

A heat pump does not of itself eliminate the need for ductwork.

But if you refer to using ductless split systems for heating and cooling that could work. See

Question: in-slab ductwork in a Minnesota home

(Jan 10, 2015) Stu said:
We are considering buying a home in MN that was constructed in 1997. It would be our perfect house in many ways. It is a high quality custom built home by a very reputable builder in this area.

However, when touring the home, I noticed that the walkout (finished) lower floor has in-slab duct work. Based on what I am reading here, none of it sounds good. Are there ways to complete this type of construction that would mitigate the concerns? Or, in your opinion, do we need to walk away? Thank you for your time.



If it were possible to guarantee that in-slab ducts were as leak-proof against water entry or condensation accumulation problems, rodents, etc. as above-ground duct system I'd be encouraged. If I were buying such a home I'd feel safer assuming that at some point I'm going to want to convert the duct work.

Question: where is water coming from when it leaks into our in-slab HVAC ducts?

29 Jan 2015 Fred said:
We have water getting in a few areas of the ductwork in a 3 unit condo building the concrete slab was poured at one time and we have footer drains along the perimeter of the entire building were is the water getting in at ?



I'd like to help but from a one-line e-text I can't know enough about your building to diagnose where water entry problems are originating.

Usual problem sources are mis-handling of roof runoff, in-slope grade draining towards the foundation, or missing, faulty, clogged footing drains. In all events, ducts in slabs are likely to give recurrent trouble as the article above explains. Please take another look at that information as it might change the direction of your thinking.

Question: heat from the furnace(s) is pumped into metal troughs/channels

(Apr 13, 2015) Amanda Dunc said:

Have you ever seen a slab ductwork system where instead of traditional vents, heat from the furnace(s) is pumped into metal troughs/channels that extend around the exterior perimeter of the rooms? (Ranch built in 1966 with finished lower level.)

We just moved into a house with this setup. There are odor issues in the basement which appear to be from foundation cracks, but I've been trying to figure out the heating system as we may have to get into this air distribution system during foundation work.


Yes indeed, Amanda. Beginning in the 1960s some builders considered long, narrow floor heating registers as a modern wat to better deliver more uniform heat to areas otherwise difficult to address, especially in the floor in front of sliding glass doors.

Start by identifying your type of heat: furnace and forced air, or boiler and hot water baseboards or floor convectors. If your system uses warm air then you may be looking for leaks into In slab ductwork as discussed in the article above.

Question: inspector commented in-slab duct work is in excellent condition and is not presently deteriorating or disturbed

(June 2, 2015) Jodi said:

The inspection of the home we are in the process of purchasing has revealed that the distribution ducts for the heating system are made of transite. Our inspector has commented that the duct work is in excellent condition and is not presently deteriorating or disturbed.

Much of the information that I am finding is regarding sealing or replacing the ductwork. However, it is my understanding that if the ductwork is not showing any signs of hazard that it does not pose a threat. Can you verify that this is indeed the case?

It is also my understanding that there is no way to test for asbestos without disturbing the material, thus creating a problem that would then need to be remedied. Is there any way to test for the presence of asbestos without compromising the current state of the ductwork?

Thanks in advance for any information you may be able to provide!


Jodi, how can we verify if this is the case without viewing all the lines, did the inspector scope all the lines? was there air quality tests done in the home? Did he test the material? Sounds like you are concerned? Ask yourself how the ducts get cleaned, and what kind of work is involved in that? Can that potentially disturb the material?

Bottom line... air quality is extremely important, and when there are risks associated you should try and reduce as much risk as possible. I think most people would agree with that statement. Unfortunately money needs to be spent and the most important thing in life is a persons health. Get professionals involved to provide you with the right information.

Was your inspector working for you or was s/he working to please a real estate agent or seller?

(June 13, 2015) Bill commented on the above and warned about conlicts of interest.

I agree with Bill. Frankly it sounds to me as if your inspector was suffering from a conflict of interest: wanting to avoid upsetting the real estate agent. I claim this because even if the ducts were in good condition - which Bill points out the inspector could not possibly know without direct examination of the entire duct runs - ducts in slabs and transite air ducts ultimately give trouble in buildings, as you'll read in the article above.

If I were buying the home you describe and there were in-slab ducts of any kind, my financial plan would provide for duct replacement and re-routing even if that improvement or correction were to be deferred. Its urgency will only be known when the duct system has been properly inspected.

Thanks for the comments Bill.

Question: heat loss through ducts in slab

(June 17, 2015) Anonymous said:

is there any heat loss in a in concrete slab duct system in a home where to ductwork located in the slab
runs around the perimeter of the home?


Sure, if the ducts are not insulated, in addition to condensation and contamination concerns both heating and cooling air will be affected by the temperatures of the surrounding concrete and soil.

Question: IAQ problem at our house we can't figure out. Terra cotta slab ductwork

June 23, 2015) Alison said:
We have an IAQ problem at our house we can't figure out. There is a strange odor and we get sore throats. We've had all the tests. It's not mold, radon, etc etc. The odor stays on clothes after we leave the house until they are washed.

The house has a partial basement and a living room is on a slab. I think the ducts under the slab are terra cotta. I can see a crack. I think this might be the source of our IAQ problem. I don't know what else it can be. I just don't know who to call to diagnose the problem so I know for sure.

I've called a couple HVAC companies and they weren't any help. Who should I call?


Terra-cotta under-slab ductwork would be a bit unusual, including fragility, too-small diameter, difficulty sealing leaks between sections. More likely the material you have is cement-asbestos. See ASBESTOS TRANSITE DUCTWORK

Look for an HVAC company or inspection company who can provide a camera to scope the ductwork to observe its condition - before you abandon it as you should.

Question: odor from vents and spaces around pipes coming through slab

(July 29, 2015) Anonymous said:

My husband and I recently bought a 1950's ranch on a slab foundation. We spent a few months painting the entire interior and putting in new flooring before we moved in. Now after living in the home for a few months, we are noticing an odor coming from the vents and from open spaces around piping under the bathroom sink cabinets.

We've contacted three companies, from HVAC to duct cleaning, for help and none of them were able to do anything for us.

Today we are moving to our fourth option of having Roter Rooter use their cameras to scope through our ducts.

We were told there is a board lining the duct and it looks like moisture may be a problem. I'm worried about the odors and gases my family is being exposed to and need some help as to where to turn for finding someone experienced enough to be able to help us. We live in Ohio. Any suggestions? Thanks so much!


It would make sense to check for sewer gas leaks and to track down a broken sewer line under the slab: use a sewer line camera scoping service company to inspect the system. Infrared or thermography can also help find leaks in sewer piping under a slab.

Question: ducts in concrete slab of my condominium: floor too hot, can't add zones.

(Aug 5, 2015) JillZ said:

I just bought a 30 year old condo and now that I am having the floors redone, we have discovered that every one of the 3 floors is concrete and all of the ducts on the 2nd and 3rd floors are in the concrete floor. The lowest level, a walk out basement, has ducts in the ceiling. It is built like a hotel!. There is also only about 14 inches of attic space.

My problem is that the top floor is extremely uncomfortably hot. I close all of the registers in the rest of the house and run the ceiling fans 24/7 but it doesn't really help. I had an hvac guy come look today and he says that he can not put in a 2nd zone because he doesn't have access to the ducts.

He thought he could put a ac unit on the roof and just the ducts in the attic, but this will require HOA approval and will have to run an electrical conduit on the outside of the building; probably not going to be approved by HOA. I am at my wits end. I can not live in this condo with the upper floors at 80+ degrees all summer. Thank you for any help you can provide.


Your AC guy may be dead right but I'd get another opinion. Usually we can locate the trunk or main air feeder between building areas and install thermostatically-operated vent dampers in those locations. Maybe not, depending on your duct layout. But I'd want to make darn sure before leaping to a much more expensive solution.

Question: concrete used for filling in in-slab ductwork

12 sept 2015 Rachelle said:
What type of concrete do you suggest when filling in a duct system? From reading over the different types, it looks like self compacting/flowing concrete should be used. Any thoughts would be greatly appreciated. Thanks!


I agree that you want the concrete to flow into the duct system and that complete duct fill-in would be best;

Some sources we have studied (JLC online forum cited above) suggested using a slurry of concrete mixed with crushed limestone that can be more easily pumped into the in-slab ductwork to fill it completely.


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