foul smell from gas furnace vents

taracolMay 5, 2013

Please help. We have a gas furnace (only 2 years old) and an odd smell coming from the heat vents. The gas company has checked the heat exchanger and says its fine and their meters do not pick up any gas or carbon monoxide readings.
We have had our furnace installer plus another company come out and go through the furnace and they also find nothing wrong. We had the drip pan cleaned and the water pump for the humidifier replaced. We ran the fan alone to make sure the smell does not occur with only that running to make sure its not anything in the heating ducts. No smell. It only comes on when the heat has not been run in a few days and it only smells for about 15 minutes then it dissapates.
It is a putrid smell and is difficult to describe. It smells like natural gas mixed in with some type of sickeningly sweet smell and something dead to me. Its not gas because no meters pick this up and it doesnt smell like rotten eggs. It is not a dead carcass because it is throughout all ofthe vents and its been going on for over a year. There is nothing else in my home that has a smell that is being picked up by the furnace that would come out of the vents. It also was ran all fall and winter long and no smell- just last April and this April. I know this sounds crazy but I assure you Im not crazy. My family members have also smelled this gross smell. We had the manufacturer (Frigidaire rep) come out and go through the furnace also. He couldnt find anything. The furnace filter is clean as well. Im at my wits end. Please help! Can you think of anything else that it could be that we havent checked or thought of? I dont want to keep living with this smell. We have young children and Im afraid.

Thank you for reporting this comment. Undo

Has the HVAC installer witnessed this smell? If yes, then what was their comment?

What is the model number of the furnace? How is the exhaust gas from the furnace vented to the outside?

    Bookmark   May 6, 2013 at 7:46AM
Thank you for reporting this comment. Undo

The installer is never here when the smell occurs. He was here one time after the smell happened and he smelled it but only faintly. I do not think he is taking me seriously. The installer was supposed to come out to my home this am with the representative from the manufacturer and instead they sent out a regular technician from the installer's company to check for a "dead animal" in my vents. They were supposed to be here to see if we could replicate the smell. The model number of the furnace is C6BA-x36c-c. I am wondering if there are any recalls on this or service tech bulletins. Any assistance you could provide would be greatly appreciated. Thanks!

    Bookmark   May 6, 2013 at 10:33AM
Thank you for reporting this comment. Undo

The model number you provided is for the coil. Do you know the answers to my other questions?

    Bookmark   May 6, 2013 at 11:20AM
Thank you for reporting this comment. Undo

Sorry about that. The exhaust gas is vented with PVC piping and is vented out the back of our home. The model number on the furnace is FGD090800507. Thanks

    Bookmark   May 6, 2013 at 2:43PM
Thank you for reporting this comment. Undo

You have a high efficiency furnace which produces condensate (water). The AC coil also produces condensation. Can you see the water drain when the furnace or AC are running?

I am not an expert on this, but I will give you one idea of a possible cause.

I am thinking that water is not draining properly and is stagnating inside the furnace. When the furnace runs daily it is not a problem since new condensate is produced. But when the water sits for several months it becomes smelly. Hopefully mold is not growing, but it is possible.

I believe there are cleaners which can be used to clean the coil. This is worth investigating. Sorry that I don't have a better answer.

1 Like    Bookmark   May 6, 2013 at 5:13PM
Thank you for reporting this comment. Undo

I'm going to go with mold or fungus of some type. I have the same thing.
Doesn't matter if its only a couple days or a month between running. When the burner lights, it burns the funk off and smells.
I installed a UV light over my A-coil, didn't help. Its coming from the burner.

    Bookmark   May 11, 2013 at 2:59AM
Thank you for reporting this comment. Undo

It was suggested to me that it may be something being picked up by the return. Can anyone shed any light on this? Im not really sure what this could be?

    Bookmark   June 2, 2013 at 4:53PM
Thank you for reporting this comment. Undo

Is it "dirty sock syndrome"?

Very common, comes from the AC coil

Here is a link that might be useful: Dirty sock syndrome

    Bookmark   June 2, 2013 at 5:13PM
Thank you for reporting this comment. Undo

No, I dont think its dirty sock syndrome. It does not smell musty. Has a putrid smell- almost like a mixture of something dead with rotting fruit (like a sweet smell) mixed with a natural gas.

    Bookmark   June 2, 2013 at 8:52PM
Thank you for reporting this comment. Undo

Yes but mold often has a sweet smell.

Once the spores release the smell dissipates. After growing new and a cycle starts you smell them again.

My money's on the coil

    Bookmark   June 4, 2013 at 10:50PM
Thank you for reporting this comment. Undo

Can you let know what you discover? I think we have the smell like you have. We built this house. When we move in the house in first year, I can smell the smell. Since this is a new house, I just can't figure out what it is. We have a 90% high efficiency furnace with AC coil and Honey Well electric filter. I also found that when I notice the smell, the smell is coming from the vents which are mounted on ceiling at "upper" floor.

    Bookmark   November 20, 2013 at 5:42PM
Thank you for reporting this comment. Undo

OMG... I am so GLAD I searched on Google today.... Anyway, I have the SAME Problem..... My Furnace is GAS.... I have the SAME SWEET SMELL coming out of my Furnace sometimes... At times, I can get a HEADACHE from it, sometimes I COUGH like crazy. It's only happened when the HEAT is on HIGH, I can barely stand it at 72 Degree. We TORE all the VENTS... Return Air and Out, FILTER is BRAND NEW and Checked the Furnace out, the only thing that we haven't done is checking out the BURNING CHAMBER...

I mean we CLEANED it all out and YES I checked everything, including a NEW Liner in the Chimney and the Intake Cold Air is BRAND NEW. I kept saying that there is a SMELL and sometimes SWEET Smell just like this post here.... Everyone thinks I'm going CRAZY :(

PLEASE, PLEASE PLEASE, let me know what you find what the problem is.... I bought this house 3 years ago, and each time we Start the Furnace, everything is BURNT out and fine, then this SMELLs comes afterward, and how can some days are fine, then other days we have the SAME SMELL????... It can't be something in the Pipes because we TORE the Darn thing off and CLEANED out....

No YOU are NOT CRAZY, if you are then I must be CRAZY too for smelling the SAME ODOR !!!

My suspicions... There must be a Small Hole somewhere in the Burning Chamber or the Metal of the Burning Chamber HEATS up and released an ODOR that normal People can't smell it. Only the sensitive People can Smell this Smell.

Honestly, I'm beginning to think I'd rather stayed COLD or use an Electric Heater and heat up the ROOMS that I need and forget about the Gas Furnace

NOTE: My Natural GAS Heater is 80% efficiency and I don't have AC in my GAS Furnace.


This post was edited by rgs03833 on Thu, Dec 26, 13 at 5:04

    Bookmark   December 26, 2013 at 4:20AM
Thank you for reporting this comment. Undo

How old is your furnace? Has a HVAC tech inspected it for a cracked heat exchanger?

    Bookmark   December 26, 2013 at 7:37AM
Thank you for reporting this comment. Undo

Hi Mike, no I haven't, since I like to do EVERYTHING on my own so I know that I have done it myself and it would help me sleep better at night since I did it myself ;)

Anyway, that is my Next Task... I will post once I know if that is the case ;)

Thank you for your Input ;)


    Bookmark   December 27, 2013 at 2:11PM
Thank you for reporting this comment. Undo

I have a similar problem, only the smell is of natural gas and I smell it in the room after the blower/fan (not just the furnace) has run for about 10 minutes. The smell gets stronger the longer it runs. The local energy company and an HVAC contractor have checked out the utility closet gas pipes and furnace and found no gas leaks, yet a combustible gas detector I bought online indicates the presence of gas in my living room, bedroom, etc. after the blower runs. Help!! I am using only space heaters 90% of the time because of this problem (fortunately I live in a small condo where using only space heaters is feasible). The contractor I hired said any gas I'm smelling is unlikely to be at an explosive level, but I'm still nervous about this!

    Bookmark   December 29, 2013 at 3:48PM
Thank you for reporting this comment. Undo

This thread has digressed from the original post, but the type of discussion here merits a comment.

If you smell gas then you need to call the gas company immediately! The gas company has gas sniffing equipment. It is in their best interest and to find any leak which has the potential of an explosion.

It is possible the smell is not leaking gas but a poor combustion or venting situation. This may mean a high level of carbon monoxide. This is potentially lethal and again warrants immediate attention!

If the contractor is says it is not a problem then find a competent contractor!

    Bookmark   December 30, 2013 at 12:59PM
Thank you for reporting this comment. Undo


OMG... Well 1 Problem SOLVED.... I just found out this weekend... That the Ballast from one of my Light is LEAKING BLACK Liquid out of it, due to HOT / Damaged Ballast. That is Part of the Smell came from.... Since I have Drop Ceilings, and the Fluorescent light was up there, there was NO WAY I was able to see if the Ballast was Damaged, until I open the light itself. Many times I am in a Store like Wal-Mart / Big Box Stores.... I Cough a lot... Now it make sense because most of their lights are Fluorescent and have Ballasts... YES, I am able to Smell BAD Ballast, LOL

OMG.... Anytime the Heat is On... I smell the Smells like the Original Post here... Plus also it felt like Radiations... Attacking my Head, LOL... But now that Problem is SOLVED....

Here is Problem Number 2.

OK, here is the Funny Part.... There is still a Smell Left.... But it doesn't feel like Radiation Attacking me.... Since the Ballast is GONE.... But it only happens on Certain days.... How can my Heater have a Brain and just put out an Odor on Certain Days.... Especially the Past two days since it's SNOWING / COLD outside?

It's been a Week since my last Post, I have been enjoying my Heater and Sleeps better at night. If there is a CRACK inside my Heater Chamber.... Wouldn't the Smell would come out anytime the Heater is on?

Also, I put a Large Exhaust Fan in the Attic... Anytime I smell the Smells, I turned it on for about 30 seconds and the Smell will be gone for a while... Air is Great again... I am beginning to think that when the Attic gets Moisture from the Air / Snow some how it seeps into the Roof's Wood... Then released it and when the Heater is on, it disburse through the entire House. Once the House is HEATED UP to about 68+ Degree... The Smell would be gone.

Another thing I suspect is... I am really sensitive and I can Smell things that Regular People can't smell.... I'm sure the ones that have the same problem with their Gas Furnace would understand. I think when the Galvanized Pipes Heats Up.... It Put out an Odor that most People can't smell it, and only the Sensitive People can smell this Smell.

I would also like to ADD.... If your Smells like BURNT Electrical or even BURN Plastics / wires, I think you would Experience this as well. Your MOTOR / BLOWER is working Harder than it should.... Like the Intake Air that is Blocked in Certain Room.... You would Experience a Smell in the Furnace that most People can't smell it, because the MOTOR Heats Up because it's working Harder than it should. This is about the Same as I am able to Smell the BAD Ballasts.

The reason I post all my findings on here is to give / help People like me an Idea of what is happening to some of us. I hope some People would take all the accounts that I have experienced and tell your HVAC Tech to Check.

I will Post my Final Finding soon I hope!


This post was edited by rgs03833 on Sat, Jan 4, 14 at 5:29

    Bookmark   January 4, 2014 at 5:03AM
Thank you for reporting this comment. Undo

"an Odor on Certain Days.... Especially the Past two days since it's SNOWING / COLD outside"

Perhaps you have an exhaust venting problem. Could snow be blocking the vent on roof? Very cold air could also make venting more difficult since it is denser than the warm air down at the furnace.

    Bookmark   January 4, 2014 at 9:43AM
Thank you for reporting this comment. Undo

Hi Mike,

I have a Dedicated Chimney Liner for my Gas Furnace also, it has a Cap on it as well. It's only about 10 Feet High since my Furnace is in the Attic. Plus, the Furnace Exhaust Fan would Shut Down if any thing is Blocked or the Exhaust is NOT doing its Job.

Also, the Chamber where the AIR is heating up is Separate from the Burning Chamber...

I think it's the Air itself... When Cold Air Heats Up.... Sensitive Smelling People can Smell this Smell...

Anyway, I will post my finding once I figured it all out


This post was edited by rgs03833 on Sat, Jan 4, 14 at 14:37

    Bookmark   January 4, 2014 at 1:43PM
Thank you for reporting this comment. Undo

I had a similar problem...couple things that helped get rid off the smell.

1) Don't keep the fan on (this I think was the main problem). Dust particles fall on the burners when their off, and when they turn on they burn off and causes a slight burning smell every time it turned on.
2) Get a good filter. Doesn't need to be the most expensive and thickest but definitely not the cheapest.
3) I placed a Ionic Pro Turbo Max air purifier in my basement, works great. Smells like there's a window open.

    Bookmark   February 7, 2015 at 10:46AM
Thank you for reporting this comment. Undo

Rgs03833 and taracol,

Did you ever find a solution?? I just read this entire thread and have the exact same problem! I need help!! We bought our house 5 years ago brand new and I've noticed multiple times a year (usually when it gets cold or there is a change in seasons I feel like) that awful, dead animal/chemically weird smell comes through our vents I've had multiple people come out and check it and they just think Im crazy. This past year (4 years later) my husband is now able to smell the smell as well It comes and goes and is so bad it gives me a headache. With 3 little kids I'm going crazy trying to figure out what it is. If you found a solution please let me know

    Bookmark   March 4, 2015 at 8:18PM
Thank you for reporting this comment. Undo

I feel the problem to the original poster is is a combination of dirty sock syndrome (as noted previously by zl700) and the heat burning off mold. What they said was the smell comes once the heat hasnt been on for a few days, then smells for the first 15 mins of it heating. I am thinking that mold had time to accumlate on your A/C coil while it wasnt heating, and when the heat turned on it burns off the mold and you get the smell. It would be nice to know if there is a constant musty smell in the summer when the A/C runs, but obviously this is an old thread and wont be answered.

I agree with Rgs03833 that another culprit could be a blocked air return or very dirty air filter making the motor work harder than usually and causing it to burn out and release a smell.

Also I read into that Dirty Sock Syndrome link posted above, and another idea from some discussion there is that the coils are not as good as what they used to be. They are often made with recycled aluminum some of which is from the landfill and may have an inherent stink to them. There are a lot of consumers recently that believe the coils themselves are defective and cause the smell. If anyone has a problem with DSS or other random smells you need to have that A/C coil removed and have a coated coil installed. Based on that link above, cleaning the coil is only a temporary solution to DSS. A coated coil is the permanent solution. If anyone has health problems very often such as breathing difficulty or sinus problems you are probably allergic to mold and have a problem with DSS pumping mold spores into your house.

I am glad I read this because if I need a new coil in the future I will go with the coated coil and not take the risk in getting a stinky coil. I am highly allergic to mold and dont want to risk causing a problem with the quality of the air in my house. As mentioned above, air purifiers do help and might be a good option for a lot of people, even if you dont have DSS.

    Bookmark   March 5, 2015 at 8:58AM
Thank you for reporting this comment. Undo

"if I need a new coil in the future I will go with the coated coil"

I think you need to be careful with a coated coil if it is a A-coil on top of a furnace. I think the coating is okay for outside coils to prevent corrosion as I think that is what it was originally developed to do. On a heat pump indoor coil it is probably okay. The temperature doesn't get as hot as in a furnace. But when they extended the application to a A-coil on top of a furnace I think it is in an environment that can be too hot for it. When it is real cold out and the furnace is on for a long time I suspect the coating can get too hot and begins to smell on its own. Now my dealer and manufacturer and coater can prove me wrong by removing the coil temporarily (at my expense I might say) but they have refused to do that because , well...maybe it would prove they have a problem.

    Bookmark   March 10, 2015 at 10:48AM
Thank you for reporting this comment. Undo

Good to know. Did not think of that. Something to ask about / research.

    Bookmark   March 10, 2015 at 1:38PM
Sign Up to comment
More Discussions
Blown in insulation vs spray foam
I am looking for advice. I have a home built in 2000...
Heat Pump in Northern Virginia
Does anyone have advice on which contractors may be...
Need help with selecting Eff Heat Pump replacement.
20 yr old American Std Heat Pump stopped working. ...
Why is split ductless so expensive when installed?
Hi, Long time reader, first post. I have a question,...
Is this HVAC system OK?
Replacing original old ~9 seer unit. House is 2001...
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™