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.

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. Be sure to see the in-slab ductwork description, problem identification and solutions described there.

On 2021-01-25 by (mod) - Is it possible to waterproof in slab air conditioning duct work?

Steve

Please take a look at the home page for this topic SLAB DUCTWORK - live link given near the top of this pafe

for which the page you're on is a Q&A collection.

You'll see that IMO an in-slab duct system is asking for trouble over the life of a building.

Yes there are procedures to clean and even to re-line such ducts but over a building's live I have found none of those to be reliable long-term. There is a particular concern for any health and safety topic when a prior "repair" effort leads us to think, in error, that a problem has been taken care-of, causing us to ignore warning signs.

I appreciate that it is far easier for me to say "abandon those ducts" than to be the person going to the cost and trouble of doing so. So sure, you can try having the in slab ducts cleaned and spray-lined with a sealant, but at the very least you'll want frequent duct inspections by camera to find where the coating didn't adhere, fell into the ducts, and there's now a pond of stagnant, contaminated water, pathogens, mold, etc.

On 2021-01-25 by Steve

Is it possible to waterproof in slab air conditioning duct work?
I have water in my ducts and don't want to move the ducts overhead.

On 2020-09-16 - by (mod) -

IM

You may get adequate heat and AC with the proposed split systems but it seems to me you'd still want to find and remove the moldy materials. If you smell mold, there is mold to be found and removed. Get rid of those wet moldy ducts.

On 2020-09-16 by IM

I have a large ranch with a 3500 square foot finished walk out lower level. My home has 3 furnaces and 3 air conditioners. One unit runs the lower level. The ductwork for that level is under the floor. We have been having a terrible mildew, musty smell for quite some time. In one room it is humid. The smell is worse when the heat is on and is slightly lessened when the air is on. The smell permeates to the main level. We have had everyone from HVAC contractors, air quality inspectors, home inspectors, thermographers, etc to investigate to no avail. Recently a camera inspection found evidence water of infiltration in numerous areas of the ductwork and found a great deal of standing water/mud in the ductwork too. Unfortunately, the ductwork for the other furnaces/air conditioners is in the ceiling of the lower level and therefore there is not any space to run new ductwork overhead with an up flow furnace/air conditioner to heat and cool the lower level. The only option that the professionals have come up with is to use a split unit such as Mitsubishi to heat and cool the level and filling underneath ductwork with concrete. They believe they can sufficiently heat and cool the level with these type of units. It would require a heating/cooling apparatus on the wall in almost every room. They are rather unattractive. Do you know if these are effective systems? Should I worry about this type of system decreasing the value of my home when I sell? Do you have any other ideas to fix the problem? The water is allegedly coming from the ground. We already have a drainage system around the home and have been told that additional drains will not correct the problem. Any ideas or help would be appreciated.

On 2020-05-12 - by (mod) -

Raphael

Finding a contractor to fill ducts in a concrete slab

Talk with some concrete placement contractors to ask them details about their familiarity with the job and how they'll proceed.

I'd be listening for someone willing to answer questions, and who is familiar with both concrete placement and also site and roof runoff control and the issue of leaks into slab ducts.

Talk with your neighbors to see if a similar house with in-slab ducts has been so treated, by whom, and with what satisfaction.

On 2020-05-12 by raphael hirsch

The house I live in has under the slab ducts that need to be filled with concrete and isolated from the other ducts in the house.
They are already disconnected from the HVAC unit.

How do I find a contractor experienced enough to know how to fill the ducts?

I live in Atlanta

On 2016-07-10 - by (mod) -

I agree with the concern. You could use a concrete pumping service who insert their pumping hose in one register while you watch for the concrete to appear at the next one in the line. Or the liquid can make the bends you describe. It's an interesting question to ask your installer.

IMO the critical feature is to seal off all openings between the in-slab ducts and the building.

On 2016-07-10 by Barry

Thank you for your response. You've said everything I was thinking but still not sure how such a shallow slope would allow the concrete to flow all the way to fill in everything, unless it was almost like a milkshake consistency. Wouldn't that just be useless for any kind of strength? Is there a way to actually pump a better strength material? I can't think of any company that would have something that could send the concrete down a vent, turn almost 90 degrees and still send the concrete to the end of the run. Any ideas there?

On 2016-07-10 - by (mod) -

Thanks Barry, we work hard to provider accurate, useful information and are really pleased when a reader finds it so.

Sonotube is particularly vulnerable to crushing as it's basically a paper product. If you're filling in the system with concrete that should be sufficient, without trying cleaning. (You could hire a duct cleaning company but frankly unless there is some unusual situation it's probably not cost-justified.)

Concrete can be poured into the duct system at each floor supply register. Properly-mixed (not too stiff) it should flow to fill the in-slab duct system adequately; if a few small voids are left in the system they're not highly likely to be a problem as they should amount to small sealed pockets that don't communicate with the building.

If there is water under your floor slab, keeping the sump pump working makes sense to me;

On 2016-07-08 by Barry

What a terrific article with so much sharing of issues and helps. Thank you. I have under floor ducts as well and have seen that they were poured with Sonotube concrete forms that have badly deteriorated from water. I have a couple of questions that have been very hard to find answers to. First, is there a way to clean the ducts out so when the concrete is poured there will be a much better bonding between the floors and new concrete? Secondly should the sump pump that was added because of the water issues in the ducts still be left in place once the ducts are filled? Also, probably the hardest question to find answers to, how do you force concrete through the ducting so they completely fill the ducts?

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 ?

JodiAnn

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.

You are welcome to give your clients or homeowners a printout of this page, and any such readers are welcome to contact us by on-page comment (or in emergency we may be able to reply by email). We welcome questions or content suggestions.

InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information provided free to the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique,questions, or content suggestions for our web articles. Working together and exchanging information makes us better informed than any individual can be working alone.

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
JodiAnn

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 https://inspectapedia.com/BestPractices/Duct_Noise_Control.php as a place to start;

Also see

HEATING SYSTEM NOISE DIAGNOSIS https://inspectapedia.com/heat/Heating_Noise_Diagnosis.php

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

Question:

(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

Reply:

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.

Reply:

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

Question:

(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

Reply:

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.

Follow-up

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

John

Reply:

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 ?

Reply:

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.

Question:

(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 ?

Question:

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.

Reply:

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.

Reply:

Bryan

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

Reply:

Sam,

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. Seeinspectapedia.com/aircond/Split_System_AC.php

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.

Reply:

Stu:

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 ?

Reply:

Fred

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.

Reply:

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!

Reply:

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?

Reply:

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?

Reply:

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!

Reply:

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.

Reply:

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!

Reply:

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.

...

Continue reading  at SLAB DUCTWORK or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see SLAB DUCTWORK FAQs-2 - more-recent questions and answers about in-slab air ducts.

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  • WHY IN-SLAB HVAC DUCTS are TROUBLE
  • FUNCTIONAL PROBLEMS in IN-SLAB HVAC DUCTWORK
  • ENVIRONMENTAL PROBLEMS in IN-SLAB DUCTS
  • AIR QUALITY (IAQ) PROBLEMS in IN-SLAB HVAC DUCTS
  • IN-SLAB DUCTWORK INSTALLATION ERRORS
  • ABANDON or SEAL IN-SLAB DUCTWORK
• WATER & ICE IN DUCT WORK
• WET CORRODED DUCT WORK

Suggested citation for this web page

SLAB DUCTWORK FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC DUCT SYSTEMS

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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