HVAC Duct odor diagnosis & cure Questions & Answers:

FAQs help diagnose the cause & suggest the cure for various types of smells traced to air conditioning or heating air ducts, registers, and air handlers.

This article series explains the diagnosis and cure of odors in HVAC ducts, air handlers, blowers, for both warm air heating and air conditioning systems.

Building Air Duct and Air Handler Odor FAQs

These Questions & Answers about How to Find, Test, & Remove Odors, Odor Detection, Smells, & Gases that Appear in Ductwork were posted originally

at ODORS in AIR HANDLERS & DUCT WORK where we list a series of diagnostic articles and steps that help track down, find, and remove the sources of smells or odors blamed on heating or air conditioning or ventilation ducts.

Be sure to review that article.

On 2020-08-02 by Ronald K Williams

Please help. I am smelling a chemical smell from a recent duct board installation. It has been about a month now. I called in a seconf reputable HVAC Company who said just use a Nu Calgon, Clen Aire product. The called in company inspewcted what they could but did not look into the return or pull a flex duct. Help is it normal smelling duct board one month later?

On 2020-05-11 - by (mod) -

Diane:

Before proceeding with a cleaning and repair we need to find where the water or leak originated - else there's not much gain in "fixing" anything as the problem can just recur.

I can't see enough about the construction of your home to follow the water back to its source, but that's what I'd ask your inspector to do.

I agree that if fiberglass type HVAC ducts or other fiberglass insulation have been wet it's appropriate to replace them.

I'm unclear about why you need a "germ killer" and less clear about what would be effective. Ask why? And get the specifics on "what" would be installed.

On 2020-05-11 by Diane

I noticed a fishy smell coming from the vent in my downstairs bathroom. I called a plumber/electrician and he went into my crawlspace and said there is water in the duct leading to that vent. I asked from where and he said probably someone poured water in the vent because there is so much of it, but I find that unlikely.

What else could cause the water in the vent and is that the source of the smell?? The same company installed a new water heater in my garage 2 weeks ago but assured me this is unrelated. They tell me they need to replace that portion of the duct and install a system to kill germs in the ductwork for $1700. Seeking a second opinion. Thank you.

On 2020-02-04 - by (mod) -

Olga

If the blower fan is OFF completely, do you still have air coming out of a return vent? If so then maybe there's wind blowing into the duct system somehwere.

On 2020-01-31 by Olga

Thank you for your response
Yes, the air in coming out of the return vent, I know it is really strange, I don’t know why?
Definitely, we need to ask to some hvac tech to come and see what is happening
Thank you

On 2020-01-31 by Smells-(mod) - Food cooking odour coming through all the return air vents in my house.

Olga

air does not normally come OUT of return vents - it goes IN, through the air handler, through the heating or cooling equipment, then is pushed by the blower fan out at the air supply registers.

If you have air coming out of return vents somethng's wrong with your duct system and

we need an onsite HVAC tech to take a look at the ductwork and at the blower fan (is it running backwards?)

Let's straighten out this question first.

On 2020-01-31 by Olga

This is the picture of the microwave. The smell is from it.

On 2020-01-31 y Olga

Hi, please help me to find how to fix this!

Food cooking odour coming through all the return air vents in my house.

The house is from 2012, two storey house.

I always noticed food odour in the second floor after cooking but I always thing that was the air traveling through the stairs until now. I just noticed a month ago, the smell of cooking food coming through the return vents when I was changing my baby in her bedroom while my husband was cooking the breakfast.

The exhaust microwave fan was on. I ran to the other return air vents and noticed the smell coming though. I just realized that I never noticed before because I was always in the kitchen when I was cooking.

I dont understand why is coming air and smell from the microwave fan when we are cooking.

I dont know how to fix this, I suppose this isn’t normal?

Air coming through a return vent?
Please, help me
Thank you

On 2017-06-19 1 by Anonymous - old rotten cabbage smell coming thru her AC vents

My mother has a old rotten cabbage smell coming thru her AC vents in her home.. the house was built in the 70s and she has never experienced this smell in her home before just as of recently. Not for sure what the issue is and my mother is elderly wit health issues. Not for sure if this smell is going to be more of an issue for her or not. Do u have any suggestions or solutions? Thanks

On 2019-12-11 by (mod) -

Paul

CO carbon monoxide itself is odorless and colorless. However CO leaked from a heating system will usually be mixed with other flue gases and might have an odor - depending on the fuel type being burned - of gases or heating oil.

The difficulty in "finding the irritating particles" is that in my opinion we do not want to hire an expensive consultant who stops by to collect some sort of generic sample, send that to a lab, and have the report sent to you. Such shooting in the dark is costly and rarely hits a useful target.

However you could try collecting particles from the surface of one of your air filters, using clear adhesive tape, and having that analyzed by a forensic lab to see if there are abnormal levels of any particular particle type.

See details at

DUST SAMPLING PROCEDURE https://inspectapedia.com/sickhouse/Dust_Sampling_Guide.php

and

TAPE & BULK SAMPLING & TESTS for MOLD or DUST at https://inspectapedia.com/mold/Mold_Test_Adhesive_Tape.php

Watch out: be sure you have working, properly-located CO detectors in the home; CO poisoning can be fatal.

On 2019-12-11 by Paul Delger

The smell is a fine dust that just goes through the air when the furnace is on. The duct guy said everything is clean. He put a filter outside one supply duct and it looks clean too. I have spent much money chasing this problem. The duct guy wants to seal the system--furnace but don't think my wife will want me to spend more money.

Extremely frustrating. I put a air purifier inside the furnace by the blower fan and that's not helping either. Do you have any other suggestions. Could carbon monoxide becoming in play here. How can I actually find the irriating particulars. Thank you so much.

On 2019-12-09 by (mod) -

Within limits (as too much filtration will slow air flow) you can add HEPA or other filtration;

But most effective is to find and clean up, remove, or seal off sources of irritating particles or odors.

On 2019-12-09 22 by Paul Delger

The smell I smell is dust. Could it be coming from the attic. The filters seem to be pretty clean

On 2019-12-09 by (mod) -

Paul

Besides having ducts cleaned, it is often important to clean the air handler itself, the supply and return plenums and the actual blades of the blower fan.

Beyond cleaning that air handling system you want to find the odor source as it is often being picked up in return air and re-distributed in the building.

The best approach is to find and remove the source of allergens; otherwise what we have, in effect, is an infinite source or problem particles that we are trying to remove from indoor air after the fact. (Asbestos won't trigger allergies and is safest left un-disturbed).

"Air purifiers" cannot purify air any more than waving a vacuum cleaner wand in the air while standing in the kitchen will suck the dust bunnies from under the couch.

I can't know what you're smelling, but sometimes you can enlist the help of an independent person who has a good sense of smell and make use of a simple SMELL PATCH TEST to FIND ODOR SOURCE to find an odor source by testing different building surfaces & materials.

See inspectapedia.com/odor_diagnosis/Smell_Patch_Test.php

On 2019-12-09 by Paul Delger

I have allergies. Had the ducts cleaned. But with the furnace on something is going through the air. Had filters put on the returns. Doesn't help or show dust.

Put two air purifiers in basement. Have a 1915 house. Very frustrating been chasing this for 2 years. There is asbestos in the basement, but can't smell that because it's odorless. What am I smelling. My mouth feels like dust and peebles and it stuffs my nose. Please help. Thank you

On 2019-10-08 13 by (mod) -

Linda

It sounds as if there is a sewer line that is broken and leaking into your heating ductwork. You'll need help from a plumber to find and fix the leak and then you'll need to replace any ductwork that cannot be cleaned and disinfected thoroughly.

On 2019-10-08 by LINDA Parker

I opened heater vent in kitchen an found 10 gals of smelly sewer water included peices of tissue an a cigarette but

On 2019-02-14 by Donna

New Goodman furnace emits noxious odor through air vents. Now that odor continues to be emitted even if the heat pump runs instead. Never smelled anything like it. It gets in my sinuses and in my throat and makes me gag. I used a charcoal filter and it worked somewhat for about 30 hours then the smell was back. I fear it is killing me and my dog. New heat pump. New gas furnace. All new ductwork.

On 2018-11-11 by (mod) -

A good place to start tracking down air conditioning or duct odors is with the list of common odor sources in the article above on this page. Pay particular attention to any possible odor sources including a dead animal that's near the return air Inlet. Of course you want to inspect the duct system from underneath the home to look for openings. If none of that reveals an obvious odor Source then it would be appropriate to have the duct interior inspected with a camera system. Let me know what you're told and I may be able to offer more suggestions.

On 2018-11-11 by Sam

We live in a manufactured double wide home with a crawl space.We have a horrible odor coming from the heating and cooling system.We have had several opinions of the smell, dead animal, sewer, etc. We get this horrible smell only when the heating or air conditioning is operating and the temperature is 80 degrees or above

.

On 2018-11-10 by (mod) -

Additional photo that looks like white sealant superficially sprayed into the HVAC duct.

A useful diagnostic thought: if you definitely feel better after spending time out of the building that can indeed suggest that the building contributes to or possibly even causes the complaint. This isn't 100% but it's a useful consideration.
IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-11-10 by (mod) -

Re-posting from private email:

I am hoping that you may be able to help me with a concern if mine. I recently moved to South Florida to attend school and am renting an apartment. I noticed a pungent smell coming from my vents and decided to try and clean them myself since the building manager did not respond to my maintenance request. What I found is disturbing to say the least.
Could you help me identify what is going on inside my air vents? I'm not sure what they are made of or if that is mold you see in the photos. Any advice is much appreciated as the building manager hasn't been much help at all and as a student, I cannot afford to pay somebody to check it right now.

I've been sick a lot lately and now think my air quality could be to blame. Thank you in advance for reading this. If you'd like to use the photos as examples to inform others that would be great of you. - Anonymous, Florida.


Moderator reply:

The HVAC air ducts in your photos are made of a fiberglass material whose surface is somewhat rough. It is normal for dust and debris to stick to the surface to a degree and normally that's not harmful (house dust is principally skin cells and fabric fibers).

However if water has gotten into the duct system from leaks or from mis-handling of condensate near the air handler, that water or moisture can stimulate mold growth (on the organic materials deposited in the ducts).

Some of the white in the photos looks as if someone sprayed paint or a sealant that partially-covered some surfaces. That MIGHT be an indicator that there was a prior concern about duct surface contamination AND that an incompetent effort was made to address it - incompetent because partial spraying of a sealant is ineffective.

Still I can't see anything definitive in your photos that would be identified as an odor source. And an odor could be coming from another building location and could be transported by the duct system.

Watch out: do not try mechanically cleaning fiberglass ductwork; it's not possible, and doing so disturbs the integrity of the duct surface, damaging it and increasing future problems with fiberglass release into the air as well as in collecting dirt and debris.

Take a look at ODOR DIAGNOSIS SIX STEPS and the articles in that series.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-11-10 by (mod) - help me identify this duct work and track down the odor source in it

Re-posting from private email:

I am hoping that you may be able to help me with a concern if mine. I recently moved to South Florida to attend school and am renting an apartment. I noticed a pungent smell coming from my vents and decided to try and clean them myself since the building manager did not respond to my maintenance request. What I found is disturbing to say the least.

Could you help me identify what is going on inside my air vents? I'm not sure what they are made of or if that is mold you see in the photos. Any advice is much appreciated as the building manager hasn't been much help at all and as a student, I cannot afford to pay somebody to check it right now.

I've been sick a lot lately and now think my air quality could be to blame. Thank you in advance for reading this. If you'd like to use the photos as examples to inform others that would be great of you. - Anonymous, Florida.

Moderator reply:

The HVAC air ducts in your photos are made of a fiberglass material whose surface is somewhat rough. It is normal for dust and debris to stick to the surface to a degree and normally that's not harmful (house dust is principally skin cells and fabric fibers).

However if water has gotten into the duct system from leaks or from mis-handling of condensate near the air handler, that water or moisture can stimulate mold growth (on the organic materials deposited in the ducts).

Some of the white in the photos looks as if someone sprayed paint or a sealant that partially-covered some surfaces. That MIGHT be an indicator that there was a prior concern about duct surface contamination AND that an incompetent effort was made to address it - incompetent because partial spraying of a sealant is ineffective.

Still I can't see anything definitive in your photos that would be identified as an odor source. And an odor could be coming from another building location and could be transported by the duct system.

Watch out: do not try mechanically cleaning fiberglass ductwork; it's not possible, and doing so disturbs the integrity of the duct surface, damaging it and increasing future problems with fiberglass release into the air as well as in collecting dirt and debris.

Because ducts can pick up and transport odors through a building, also take a look

at ODOR DIAGNOSIS SIX STEPS

and the articles in that series. https://inspectapedia.com/odor_diagnosis/Odor_Diagnosis_Steps.php

Additional photo that looks like white sealant superficially sprayed into the HVAC duct.

A useful diagnostic thought: if you definitely feel better after spending time out of the building that can indeed suggest that the building contributes to or possibly even causes the complaint. This isn't 100% but it's a useful consideration.

On 2018-01-24 by Erin

My neighbours are heavy pot smokers and it's getting into my house. It's a couple townhouse and we share the back wall. The scent is strongest in my basement, but it permeates the whole house. Is it a problem with my furnace? Is it drawing air from their house or an outside source? How can I prevent this?

On 2017-11-24 by (mod) - start by looking for an odor Source near the return air inlets

I would start by looking for an odor Source near the return air inlets

On 2017-11-23 by Dan Taylor

Office building with sporadic odor of grilled steak. Any thoughts?

On 2017-11-13 by Chris smells like citrusy or some other chemical.

We had an ozone shock treatment done overnight in a 2 story home to eliminate a coking/mothball smell. Prior occupants were Indian (no offense but their cooking odors are strong). Home was vacant at time of treatment. Carpets were cleaned prior to ozone treatment on the same day.

Now the cooking/mothball odor is gone - however there is another smell in the home. It's hard to describe but smells like citrusy or some other chemical.

I believe it was from the carpet cleaning. The smell is coming from the HVAC system when it runs. When we run the heat it is stronger. The drywall seems to release the smell too and seems strongest where supply air vents are

. I belive the source of the odor is from the air plenum boxes in the HVAC system. The boxes are ductboard (tin or aluminium walls with fiberglass insulation panels on the interior). I belive the insulation panels on the inside of the boxes picked up the odor and is emiting it now. Any feedback on this?

On 2017-11-05 by Kim K

We recently replaced some flooring in our ranch home thst is on a crawl space (kitchen, dining, living room and hall).

We did not relace the bedroom carpet or the 2 bathrooms yet. About a week or so after we started smelling a musty odor in our hall bath. We thought maybe towels left in bathroom from shower, but it got stronger and we now smell in the master bathroom.

The smell appears to be coming from the vents, and smells kind of skunky. We have been running a dehumidifyer, remove all towels after showers, etc, and the smell is still there. Could this be mold? A leak in our ductwork? Should we get a mold inspection? Duct inspection?

On 2017-10-17 by Kathy

Your editor's need to correct this. Embarrassing for a company to post this on the web with misspellings: Check out how ANIMALS is spelled.

Checklist of Sources of HVAC Air Duct System Odors / Smells
The checklist below addresses things to check if odors appear to be present in or coming from building heating or cooling ductwork, air handlers, or blower compartments, or at the heat exchanger.
• ANIMNAL SMELLS may be due to current or prior pets

On 2017-09-13 by "A little Anxious"

I live in a very old duplex with a furnace that looks just as old, and the past few days there has been an strong odor coming from the furnace area (closet). The only smell I can "compare" it to is mothballs, which I do NOT use. My issue is this, is the odor hazardous/harmful? I have reported it to my landlord, but should I wait patiently on him to check it out, or should I have a professional take a look, or call my gas company and report it?

On 2017-08-10 by Taaj Ewing

How dangerous is it for breathing in these smells and bacteria

On 2017-06-05 by (mod) -

As if it would be worth using an inspection camera to examine that section of ductwork

On 2017-06-05 by Jan

There's slight chemical odor that I noticed coming through the air vent only in the room where Im working on my computer - it affects my throat - and I checked the other vents in the other rooms and there's no odor coming through any of them. This is a small apartment in a building at least 40 years old

On 2017-04-13 18:50:18.570011 by (mod) -

Talk to some potential onsite investigators, ask about their experience with this sort of odor tracking;
Do not pay someone to stop by and "do a test" as such would be of little benefit, not diagnostic, and not prescriptive. If there is a problem source it needs to be found and corrected.

On 2017-04-13 18:48:31.360732 by Anonymous

thank you very much for your time. This has been an ongoing issue .

On 2017-04-12 by (mod) - dirty socks odor in ductwork may be due to mold

Anon:

I cannot say with any confidence how safe or unsafe an odor is from e-text alone. That's a reason for an onsite expert.

There are some molds that smell like "dirty socks" and in general, IF mold is the odor source, both MVOCs and some airborne mold spores can be a health hazard.

You might want to use the search box just above to look for WHEN TO HIRE AN EXPERT to think through just how much for-pay expert help is warranted.

On 2017-04-12 by Anonymous

do you think it could be harmful to breathe

On 2017-04-12 by (mod) - inspect the air handler and ductwork for having been or still being wet

T

I would inspect the air handler and ductwork for having been or still being wet; those conditions can produce mold growth that smells.

I would also double check that there are no sewer line leaks that leaked into the ductwork as I've on occasion found in basements and crawl areas.

I would check the location of the return air inlets to see if the system is pulling air from a smelly floor drain, plumbing fixture, dry plumbing trap.

Finally, if this is a new problem I would ask what has changed as that can give clues about where to look further.

On 2017-04-12 by teacher

our building has a fecal/smelly foot odor when ever the ac is turned on . any thoughts on what it could be

On 2016-11-25 by Anonymous

we're getting a cooked cabbage or cauliflower smell coming through a couple of vents. we live in a manufactured home and a couple months ago had all the duct work replaced. the smell is not continuous. any ideas? who would we contact to check this out?

On 2016-11-13 by (mod) -

Sarah this doesn't sound like a simple air duct odor since your house is leaning and cracked. You haven't said how much lean, how bad are the cracks, where they are, nor what sort of smell is present. So I can but warn of some obvious possible immediate serious safety hazards:

GAS LEAKS: if a building has moved, from settlement, frost heaves, earthquake, etc. enough to damage gas piping there is risk of a gas leak and a fatal fire or gas explosion.

Sewer leaks: similarly, a broken sewer pipe risks both health hazards and a methane gas explosion.

If there is serious structural damage there is risk of a collapsed building and injuries or worse.

Don't panic, but IF you have reason to suspect ANY unsafe conditions in the home it makes sense to get everyone out and call emergency services from another location. 911.

If there is not a real urgent problem (ok so you actually can breather), then you may benefit by asking for a professional home inspection by building expert to help you sort out what's going on. At the top of this page at the right line of links see EXPERTS DIRECTORY

On 2016-11-13 by Sarah Cooke

Our house is leaning and has cracks we are ill including the cats it smells and we get burnt and can't breathe

On 2016-09-17 1 by (mod) -

Musty usually means mold or wet mold; find and clean the odor source. Find and fix the leak that caused it.

On 2016-09-17 by Prabhu nath

Musty or other types smell co in our shop what can be problem & solutions?

On 2016-07-22 by (mod) -

Yes there could be a dead animal in the ductwork; why not ask for an inspection (perhaps by camera) of the duct system?

On 2016-07-22 by Kristi

We bought our house a year ago and we have noticed that occasionally we get a fowl smell down our hall and in a certain area of the house.. Upstairs only, never in the basement.. It seems to run along the main duct for air conditioning and heating.. It smells fishy (stinks pretty bad).. We had our septic tank pumped thinking it was that and it wasn't. We have run water in the bathroom tubs that don't get used much to see if that was it and it still happens. Could it be something in the duct and if so what?

On 2016-07-21 by (mod) -

Ray it's an economical approach that is worth trying.
If you call an industrial hygienist be sure that the person has experience with this specific sort of issue. Otherwise you risk hiring an expensive consultant who does little that's useful.

On 2016-07-21 by Ray

Thanks for reply, I will run the patch test but smell is not confined in single room, I smell it at stairs (2 intake vents closeby), restroom, 2 rooms on other side of stairs ..

These are all on second floor. Very less (<5% smell in few specific areas on first floor) like kitchen nook- on opposite side of stairs and there is no smell in kitchen that is in between or in any other area on first floor.
if i want to call someone to test who would be the right people ?

On 2016-07-20 1 by (mod) -

"Old building smell" is a familiar but troubling term; the smell comes from something besides mere age.

I suggest searching InspectApedia for SMELL PATCH TEST KIT to read a simple procedure for narrowing down the probable odor source in the smelly room.

On 2016-07-19 by Ray

We moved into 30 Yr old house in Houston and it has this peculiar smell on second floor(mostly) but very little hint on first floor too. We though it was carpet and got it replaced, smell reduced but it is still there.

The smell get stronger with increase in temperature, at temperature below 73 it is not noticeable much but the harmful effect is still there, the smell also get stronger if I close the Rooms door, it seems with no circulation the intensity get stronger at same temperature. I have changed all filters and it did not help.

Called the carpet guy and he says it is old building smell and not mold smell ..I am out of ideas ...Help!!!

On 2016-06-22 1 by Anonymous

great suggestions - thanks, will look for those and let you know what I find!

On 2016-06-21 by (mod) -

I'd look for a condensate system leak or a spill in the air handler or ductwork.

On 2016-06-21 by Terry

Thank you for that information. There is no odor near the air return inlets. The smell started shortly after we had the supply ducts replaced. Confusing to me is that I can smell it when the AC is running but not the heat. Maybe the heat is masking / destroying the smell?

I have a flat roof (live in the desert SW) and this system is mounted on my roof, the AC unit and all the ducts which penetrate the roof directly to the supply registers. I would hope my system is well enough sealed that it would not pull air in from the outside but I suppose that is possible. Even so, I don't ever smell that metallic type of smell when I'm on the roof.

I'm familiar with electrical smell (overheating, burned wires, etc.) and this is nothing like that.

Any suggestions on a deodorizer I could atomize in the returns to see if I could mask it or maybe eliminate it if it is something organic?

On 2016-06-17 by (mod) -

Terry, refrigerant itself is odorless; oils or spills into the air handler or duct system as well as odor sources near the air return inlets often track down the source of an odor. Identifying a smell by its odor is a useful step in diagnosing the trouble but it's no surprise that that's not enough or that it leaves everyone uncertain. A visual inspection for leaks and spills, for overheating electrical components, and for leaks anywhere in the return ducting may help find the trouble. Keep me posted.

On 2016-06-17 by Terry

When I use my AC system I get a 'metallic' smell in the house coming from the ducts. This is a combination heating / cooling unit and I don't get the smell in the winter when the heater is working. That tells me the smell is being masked / eliminated by the heat, or the AC system itself is causing the smell.

I've had two different HVAC contractors out for other reasons and they can't identify the smell. Any idea what might be causing it?

Question: new plastic odor from vents

July 9, 2014) Kay said:
I have a smell coming from the air conditioning vents. It smells like new plastic. What could be causing it?

[Click to enlarge any image]

Reply:

Kay

Possibly a burning electrical motor, wire, wire insulation, or an odor being picked up at an air return and transported through the building.

Question: chemical odors from central air system

(Aug 3, 2014) bob said:
my central air when its on smell like lawn chemicals where is the intake on my central air system

Reply:

(Sept 6, 2014) josephine said:
I also have a smell coming from my a/c system. But I have been in Wal-marts and planet fitness,and have smelled the same thing. A mixture between chemicals , and a sweet smell. I live near 29 south.

Question: stale odors from ductwork

(Nov 12, 2014) fruce bagheri said:
I have a stale smell coming through the duct work when the heat goes on? what could be causing that?

Reply:

Check for leaks into the duct system or dirty ducts that need cleaning.

Question: Foul urine odor from ductwork

There is a oul urine odor coming from our ductwork

Reply:

Look for animal urine near an air return or look for mice or other rodent invasion of the ductwork.

Watch out: for bacterial or viral hazards from mice or other animals in the HVAC system

Question:

12/28/2014 Anonymous said

I have an intermittent stale dry ice odor coming from ceiling vents during heat cycle only, not ac. Outside temps have been between 40s & 60s. Not sure if defrost cycle has ever kicked in, or aux heat. Unit is 8 mo old. Any thoughts anyone?

Reply:

I'm not sure what dry ice odors means - dry ice is frozen carbon dioxide or CO2 which is odorless. I'd give the HVAC service company a call to ask for assistance.

Question: Odors in Texas duct work

(Jan 25, 2015) Jay said:
I live in Texas and we've had a couple of weeks of cool weather that required us to use the heater. It warmed up and we turned on the a/c and a foul smell came from the vents. It smelled like something had died. Heat is back on, no smells. What could be causing this problem wit a/c and how do we fix it?

Reply:

Jay,

Since we can assume that the same air handler and duct system were in use for heating as for cooling, I'd start by looking right in the air handler for a problem in the heating unit.

Question: sewage odors from ducts

(Apr 12, 2015) Anonymous said:
why at different times a sewerage smell comes out of our air vents downstairs and not upstairs

Reply:

Perhaps that's where the dry plumbing traps are located.

Question: old ductwork, plastic musty smell

(Oct 17, 2015) jeff said:
I have remove some of the old section of 6 inch duct work and replaced it with flex duct and we have been getting a plastic -musty smell in one of the rooms . What might that be ?

Reply:

dirty ducts, leaks into ductwork, spills or leaks in the ceiling, spills or leaks near an air return, open return ducts in the attic

Question: Odor coming out of Trane XL20i HVAC system - acrid, burns the throat

(Oct 22, 2015) joyce said:
Since July we have had an odor coming from our

HVAC...it is a Trane XL20i and it is
pretty bad..it is either an oily smell
like today or acrid where it burns my throat at night.
Our smell is pretty much in our living room...master bedroom
and a couple of days ago in our family room.
Our home is one level with an unfinished basement.

Reply:

Joyce:

Inspect the air handler - blower - first for a leak or motor or electrical problem, all of which are unsafe;
IF the ducts and air handler are themselves clean then I'd look fdor an odor source close to the air returns for the system

Question: bad smell from wood heater when runs hot

(Oct 24, 2015) wayne said:
I get a bad smell only from my wood heater, only when it runs hot but not from my propane

Reply:

Watch out: I would start with a chimney inspection by a pro: for possible creosote hazards - watch out you could be at risk of a house fire.

Also have a check for gas leaks related to heating piping or controls or connections. also unsafe with obvious fire and explosion risks.

Question: sulfur rotten egg smell from AC vents

(Oct 31, 2015) amaraa said:
I have a question. I have a restaurant and suddenly we started getting sulfur or rotten egg like smell from our AC vents. We thought it was coming from the AC unit and had the vents and duct cleaned but the smell is still there. Surprisingly, we have air vent in our restroom and it is not connected to air vents or ducts. The smell is coming through the air vent in the restroom and we don't know and cannot find where it is coming from. Any ideas please help.

Reply:

Amaraa

Refrigerant itself is odorless; so I figure there is an odor source that's being picked up and distributed through the vents: look for a backing up sewer line or drain opening close to a return air source in the system; if you can't find a likely culprit it might be that there's a dead animal in the ductwork.

Question:

(Nov 15, 2015) joyce said:
Since June we have had a kind of acrid exhaust like smell coming out of our vents from our Trane xl20i HVAC unit.
We have had our unit serviced and our air ducts clenaed but we still have that small. I thought it was strictly
just an AC problem but in November we still have it.

I am wondering why it won't go away. We haven't used our fireplace in many years so I don'
think that could be it.

Anyone have any ideas
PS our house is a one story with an unfinished basement.

Our air ducts were cleaned on Thursday and the smell came back today (Sunday).

Reply:

That suggests that if the ducts were really thoroughly cleaned (and are not fiberglass lined inside) - all ducts and all of the air handler - then the problem is not in the ductwork but rather is being picked up as an odor entering the return duct system.

Question: metallic smell from HVAC ducts

2016/06/16 Terry said:
When I use my AC system I get a 'metallic' smell in the house coming from the ducts. This is a combination heating / cooling unit and I don't get the smell in the winter when the heater is working. That tells me the smell is being masked / eliminated by the heat, or the AC system itself is causing the smell.

I've had two different HVAC contractors out for other reasons and they can't identify the smell. Any idea what might be causing it?

Reply:

Terry,

HVAC refrigerant itself is odorless; oils or spills into the air handler or duct system as well as odor sources near the air return inlets often track down the source of an odor. Identifying a smell by its odor is a useful step in diagnosing the trouble but it's no surprise that that's not enough or that it leaves everyone uncertain. A visual inspection for leaks and spills, for overheating electrical components, and for leaks anywhere in the return ducting may help find the trouble. Keep me posted.

...

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