Revenge of the Smelly Ducting

For about a month now, we’ve had this odd odor in our house. It started out in our laundry room, on the east end of our main floor. Then we noticed it in our bedroom, on the west end of our 2nd floor. Since then, we’ve noticed it in almost every room in the house on different days, but never all over at once. It’s always one or two rooms, but they could be on opposite ends of the house.

I few weeks ago, I realized that the smell was coming from the furnace vents. After some experimentation, I noticed that running the furnace made the smell go away. It got worse when the temperatures were warmer, and the furnace wasn’t running.

So we called out our local heating/plumber guy. After they were out here three times, they did find a couple of problems with our furnace, but no gas leaks or anything that could explain the smell — which, by the way, three different employees couldn’t identify. They even left an air charting unit with us, which ruled out things like carbon dioxide, carbon monoxide, and particulates. It did helpfully notice that there were odors, but didn’t tell us what they were.

So here we are, still smelling this…. smell. It defies categorization. It mystefies experts. Something like a cross between dirty laundry, mold, and a skunk. And yet…. none of those, either. It’s weird.

I’ve taken to closing the vents in our bedroom before turning in for the night if the smell is bad in the evening.

So, I’m appealing to all the bloggers out there for suggestions, short of selling the place and moving to town :-)

Oh, and this is not the first time we’ve had odor problems here. However, the cause the first time was immediately apparent and thus could be eventually dealt with :-)

251 thoughts on “Revenge of the Smelly Ducting

  1. I have been driving myself and everyone around CRAZY with my own stinky house problem. Seriously, smelling everything and begging all who enter my house to help me figure this out. In one of my many hours logged searching for an answer, I came across a post describing “Dirty Sock Syndrome”. It may be the cause of some of your unnamed stank…the hubbs has gone to the big orange store in search of coil cleaner. *fingers crossed* Just google it & hopefully it will help some of you. good luck guys!!


  2. I stumbled upon this forum hoping to find an answer that was better than I had originally thought. Unfortunately I’m pretty sure I know what my problem is. This evening we started to get a smell throughout our house that smelled like a burning skunk. Originally, we thought there was a skunk outside until it started smelling like it was burning. We evacuated the kids from the house in case there was a fire and started searching for the source. I was in the process of calling the fire dept when my husband figured out it was coming from the dryer. (Our utility room houses our dryer as well as the A/C unit that pumps air through the vents all over our house. Which means…yup this smell has invaded the whole house. We’re positive it’s coming from the dryer. I was hoping to find something on here that would cause this smell but I’m pretty sure now that when the smell fades a bit tomorrow and we open it up, there will be a fried skunk in that dryer. Yay! something that is NOT covered under my warranty. A warranty that I’ve had all of 30 days since I had to pay $250 to fix the damn thing. Guess it’s just luck.


  3. In our house it must have been the p valve, too. A furnace put in recently shares some pipe with an unused washing machine. When we ran the washing machine, the smell went away. Thanks to all for helping us figure it out. Good luck to you.


  4. Interesting. I have a chimney sweep in my house at this very minute finishing up. My appliance man came yesterday and took my 1 year old dryer completely apart, front and back, as he was sure the terrible odor was coming from a dead rodent. Dryer clean. Chimney sweep found a dead rodent in my dryer vent to the outside. snaked it and shop vaccumed the vent out and there is was. My sweatshirts and knit tops, and jeans would come out of the dryer and smell like smelly feet. very offensive. This past weekend the laundry room was very offensive. Caught the dead culprit.
    Have a chimney sweep out to check your dryer vent. Let me know. good luck


  5. A few weeks ago in my 13 year old’s room I noticed a bit more “stink” than the usual combination of food, hairspray, perfumes, etc and my first reaction was “What have you lost in here?!!” thinking it was a half a sandwich or spilled drink. As it got worse and worse, I came to realize it was probably something dead.

    We live in a 2 bedroom mobile home with a bedroom on each end. It could only be smelled on her end of the place . I sent my husband (who is NOT a handy guy, and that is putting it mildly) underneath looking for bodies. He couldn’t find one. That is not to say there isn’t one there. I have pretty much determined it is in the heating duct. which is on the floor….we cleaned that out as much as we could, and this morning are planning to go get a shop vac. This morning…I could start to smell it in the living room which is the room next to hers.

    Any ideas for order absorbing products? I cannot afford the hundreds of dollars it takes to get someone professional to do this. It’s early April and it’sonly going to get warmer. And it’s a trailer!!!

    I am remembering that before this started, the hubby found a dead mouse lying near the refrigerator. One of the cats had gifted us. I’m thinking babies in the duct




  7. Hi Tim,
    I want to thank you for posting your solution on this site. We found the exact thing you did in our soffit. We couldn’t figure out where that smell was coming from for 2 years now, but we took your advise and couldn’t believe the size of the hornets nest we found. My husband was getting physically sick while removing the nest. The smell was so bad. We sprayed it with bleach and we’re sure the problem has been solved.

    Thank You Again


  8. Soo happy to find this site! My husband is ready to divorce me over this house stink issue. We just bought our house last year in a wonderful neighborhood that we love. At first I thought the smell was from the older woman who had lived there alone for many years. Then I thought it was her animals—-she didn’t have any! So now after reading all of this I am on the hunt for sewer gas and leaks. We have radiant heat in our floors (water!) but the smell is located in two main areas—the furnace room and the family room. The family room has electric heat in the floor and a pergo floor on top. Numerous places for smells to escape. I am going to start with the traps—-and then toilet seals and then we will tear up the floor—-I have never lived like this and I refuse to now—-


  9. Hope this helps you all. We tried everything and nothing was working just like evertone else. But my husnand decided to try and clean the furnace components not the duct work. We have been smelling only traces of the smell now and it is getting less and less as the days go by. First turn off the breaker to the furnace, take off the front panel, unscrew all screws that connect the fan casing, slide it out and put it outside, spray it off with an air compressor and then go in to the furnace area and find your way to the heater coils, do not touch them but spray them off with the air compressor very well. Wipe the inside of the furnace to get rid of all the dust bunnies that collect inside. Put everything back together, open all vents and turn the heater on about 75 degrees and let run for quite a while. Open windows to get air circulating inside the house, this has worked for us and is cost free so good luck. Our furnace is only 14 years old and is an electric forced air heating system. coleman


  10. Our house smells like dead animal. Smell gets worse at night? My husband has checked the ducts and he insinsts its a dead animal in there but can’t find anything. It’s been 2 weeks….any ideas?


  11. I have the same problem, strange unidentifiable smell, not CO2, no dead animals & had the furnace professionally cleaned, sanitized and serviced. The smell turned out to be coming from my chimney. There was negative air pressure in the house, so my furnace was sucking in air from outside through the chimney. The SOLUTION was to run a type of chimney liner (can’t remember the technical term for it) from the top of the chimney to the furnace. This makes my wood burning fireplace useless, but eventually I’ll convert it to gas.

    The Long Story of how I figured this out:
    I had the furnace cleaned & sanitized. The smell came back a couple of days later. I would clean the filter out all the time and get sanitizer to spray in the vents, I would notice an improvement for a day or so.

    The smell was worst from the air intake. If I left it too long eventually all the vents would smell.

    I have had this for 6 months. I needed to do some roof repair around the chimney, it was the roof repair man working on my chimney that pointed out that I didn’t have a liner running to the furnace (the liner has a cap on the top to prevent water from getting in). So I mentioned this problem I was having with smell from my furnace, he was right, a chimney liner solved it.

    The musty, yucky smell was coming from the chimney, rain was able to get in & the chimney was very dirty.

    Now its summer time, so the furnace is only running at night, but so far so great!

    Now that I know all that I do, here’s an idea: If you are like me and have a wood burning fireplace and your furnace vents into the same chimney (and you don’t have a chimney liner for the furnace, with a cap on top), you could try burning something in the fireplace and see if the smell back drafts through the intake vent.


  12. Test the vents for meth, you can pick up a home test and it will probably cost you $45 but is well worth it!! Good Luck!


  13. We’ve been having a similar smell in the house for the past 3-4 days. It smells more like paint thinner or varnish. At times it’s faint, other times it’s stronger. I haven’t yet pinpointed where the smell is coming from…. I’ve tried changing the furnace filter, ensuring that all the drain traps have water in them – still the smell lingers.

    We have central A/C in the house (forced air), natural gas water heater powered by electric; but still haven’t been able to determine if this smell is linked in any way to the furnace. The house is about 10 years old.

    Anyone else with similar paint/varnish type smells??? Email me directly if you can:



  14. Yup, my stinky air vent in the spare bathroom turned out to just be the p-trap in the bathtub being dried up…I ran the water for 10 seconds and voila! Smell gone. Thanks, Mike Steese.

    Good luck to all!

    Cheers! :)


  15. Thanks Mike, the dried up p-trap in the spare bathroom was causing that bathroom’s air vent to seem horribly stinky…ran the tub water for 10 seconds and problem solved! Well played, sir. :)


  16. The smell is moisture on the heat exchanger from lack of use. Open your windows at the start of heating season and run your furnace hard for about 30 minutes. The smell will vanish for the duration of the season unless you run the air conditioning or go for a long period without using the heat.


  17. Every year when the weather starts getting cooler or in the springs when it warms up (just above freezing)our house smells like sewage. This has been happening for about 4 years. The smell is definately coming from the cold air returns. The smell is so bad we are considering moving. Does anyone have a solution? We have tried calling plumbers and furnace cleaners and they can’t find anything wrong. We don’t have a basement. The furnace is on the main floor.


  18. We have a similar problem. When the heater turns on (but not the A/C) two of our bedrooms get this sickly sweet odor that comes from the heat registers. The furnace is in the garage, and the heating/cooling ducts run under our 1 story house in the crawlspace. We had the entire system professionally inspected in Spring 2010, all ductwork was hooked up correctly and the entire heating/coolong system as well as the dryer vent were cleaned out. Over the summer, when the A/C would run, but not the heat, the smell was not evident. We also had a pest control company seal up all outside entries to the crawlspace and they didn’t find any recent (within the past few years) evidence of “critters” under the house. The smell is in two adjacent bedrooms, and is stronger in the one that is closer to the outside A/C unit. But since the smell doesn’t occur when the A/C is on, I don’t think the A/C is the problem. Any suggestions?


    Ed Cassada Reply:

    Have you had a solution. We had new gas furnace installed and since sometimes we get sicky sweet smell from input vents when furnace is running. So far no one can find problem. I’m desperate!


  19. I had a recommendation to replace my furnace plenum and wonder if it’s really necessary. When I smelled something awful in the furnace vents recently, I looked inside each one for dead animals and saw a 2″ hole in the kitchen floor duct. It was a perfect size for cold rodents that found a way into the ground level crawlspace. I’m still working on sealing the crawlspace which is an opening around plumbing in a really awkward location under the kitchen sink. So far the rats are winning. I did have the duct replaced and the brave young man crawling in that claustrophobic space said rats had made a toilet in the plenum and the metal was at risk of rusting through. The source of the foul smell turned out to be a dead rat in a nest in the garage next to the furnace — outside the HVAC system. We traced the smell and removed the sheet rock from the front of a platform on which the furnace sits with the plenum below. The HVAC crew gave a bid of $1300 to replace the plenum and clean the ducts. I’m still somewhat questioning how much risk of rust there is and if we couldn’t just clean the plenum with PineSol which I doused a couple of times in the cleaned-out rat nest and got rid of the smell. I guess it’s just as much work to get into the plenum to clean it as to replace it. I’m convinced to do something because when I turned the furnace on this week, I got a queasy stomach and headache. Maybe it’s just my brain knowing I’m breathing rat poo.


  20. I am having a similar problem…the smell is only in the lanudry room. Baseboard heat, elec water heater…did you ever figure out what this was?


  21. HELP! a few weeks ago I came home to a ton of sewage backup all over my bathroom. It had come up through the bathtub, toilet ,and sink. I found out the city sewer dept had been pumping the sewer lines. Aparantly, I am the last home on the leg of the line (perfect). The sewer water drained into my bayhroom vent. (YUCK!!!) Now my whole house smells like sewage. I have tried pouring bleach into the vents. The smell will not let up! Does anybody have any ideas???


  22. Thank you all for your comments and solutions tried. I too have been experiencing this horrid smell. It started in the garage (which is attached to the house and where the furnace is) and we thought it was a dead cat, or rat or squirrel… we have lots of all in our neighborhood. No signs of droppings, feathers, nests etc. so we thought it was in the furnace. Cleaned it out, replaced the filters, moved stuff and looked in all the nooks and crannies but found nothing. Then I read your solution and realized we have an upstairs bathroom that rarely gets used. I ran hot water in the tub for about 3 minutes and scrubbed the toilet and flushed it several times. I went back downstairs to the garage and the smell was gone! Thanks again for this amazingly easy and quick fix to a horrifying, stinky problem!


  23. Ok, my situation doesn’t seem the same as anyone else’s.

    While I haven’t read every comment as there are way too many, I did search kws & no one talked about health issues.

    I have a sweet chemical smell that’s coming through 2 vents either just before the heat turns on or during. Why it only seems to come out in one area of the house I have no idea.

    When I bend over to smell I can’t smell anything.

    I had no idea what the smell was b/c I’ve never experienced this before in all my years of living in numerous different houses, so I thought it would go away.

    Called in the fire department & Union Gas – nothing, it’s not a gas issue.

    Then 2-3 days afterward I started to feel sick.

    Now my throat is all sore, my chest is tight, my heart is beating really fast. I want to run screaming from my home, but I have nowhere to go. The taste is in my nose & mouth & I can’t get rid of it.

    What is strange is that it doesn’t seem to start up until after 10 pm. I can smell it faintly during the day, but it really starts to permeate the house at night time & all throughout the night & I’m up then so I can barely sit on my coach without feeling sick.

    At this point I’ve determined just based on my reaction, that It’s clearly something toxic.

    During the day & in the early evening 2 others said they couldn’t smell anything. Both came over after I had already started making food & so that must have masked the smell.

    Also I think you have to be in the house for a while to get accustomed to it plus, if they don’t have a good sense of smell, they won’t smell it.

    I’m finally bringing in someone to look at the furnace, but I’m petrified it’s not that. This is going on day 6 now.

    If anyone can suggest what it is pls. help. It doesn’t smell like a dead animal at all & there’s no air cleaner attached to the furnace to turn off.




    Ken Reply:

    Did you find out what was wrong? I would say that it’s the exact same thing for me. It’s been happening for a few years off and on (still happening). But once that smell gets into my body, it kind of stays there. Even if I go outside then cough or exhale, I can smell it. And it happens at two houses. Same smell. Strong when the heat/ac comes on.
    Had ducts cleaned and furnace replace(crack in exchanger) for one of the houses, but the smell is still there.
    The worst part is that no one else who lives in the house seems to be affected by it, and they kind of don’t even notice the smell.
    I’ve lost a lot of sleep because of this. Because I know that when I wake up, I will wake up feeling sick.
    In your case, does it also kind of dry out the top and back of your throat?
    I have a huge feeling that it has something to do with the sewer. Or it could be mold.

    I think sometimes our health symptoms can better tell us what it is, then we can better find the source.

    Hope you fix your problem soon.


    Sheryl Reply:

    We had a terrible smell..almost ammonia like that flared up my asthma and made me feel awful. It was much worse at night and then got better throughout the day. It turned out to be a raccoon, who was peeing and pooping and nesting. He would sleep during the day, but get active at night. Finally got rid of it and reinforced the wire vents that allowed him to get in the crawl space.


  24. ok so i am reading some of these post and agree I ALSO HAVE THE STINK I have been tracking this smell which sometimes i believe to be coming from my drains in the kitchen. Even my tile counter tops stink. This smell comes and goes but drives me insane! It is definitely worse in the winter or when it is windy. I could stick my nose down to the drain in the kitchen sink and smell it too, as well as the range burners. I think I found it I smelled it strong tonight in the vent of the range hood. I turned the fan on and the smell disappeared…turned it off and it came back. I am going to have my hubby get on the roof tomorrow and find a way to check the flap and make sure nothing is stuck or died in the vent duct!! Rooftop vents are very troublesome at times so check those!!


  25. Solution to Bad Smell – Scenario 1. New house 2. Just installed new heating vents (replaced asbestos pipes) 3. Bad smell coming from heating….. I have in intake air unit in the ceiling that draws air in and was smelling of death. I just replaced all my heating vents/tubes under the house and a few days later had a horrible smell. Thinking that a rat/squirrel/mouse got caught in the pipe I followed my nose to my daughters room to find the problem. I removed the pipe and looked into it……nothing, but the smell was strong and obviously getting into the pipe somehow. I followed the trail (under the house in a 2 ft crawl space to a section of insulation that was stapled around a heating pipe. I ripped the plastic off and insulation and found rat poop and finally out pops a dead rat that was nestled next to the metal heating pipe and fumes exuding into the pipe. Rats/mice make homes in the insulation and will live next to the pipe for warmth. I thought it could be the sewer gas at first as we have two bathrooms we rarely use, but 3 days of investigation and a little obsessive compulsiveness by myself I found the dead rat. If I didn’t find it then it would be there for weeks rotting as flies, maggots, etc would not be able to get to it. So even though I smelled it 4 or 5 rooms away is b/c the smell would travel through the heating unit and tracking it down was the hardest part. You may think it is right above you, but in the end it was 100ft away in the insulation under and outside the pipe…….my xmas is saved.


    Chad Reply:

    And thank you to all of these posts as I did try everything to the sewer gases, smelling the walls/vents/floors……… Smell comes and goes depending on where the air is travelling……..


  26. I bet it is a dead animal. Look in areas accesible to food or holes and roof is another good place to look, but if you are turning the vent on it is pulling air from the kitchen and not pushing air into the kitchen so it is most likely pulling the smell from under oven or around there.


  27. Old house solution… Our dead animal smell lasted so long that I knew it had to be a large animal. There is no way for a large animal to get into the house/ductwork. In the middle of the night it struck me that there is only one place that a large dead animal could be that I couldn’t see — under the cement front porch. I dug a big hole, crawled under the edge of the stucco (goes to the ground) and there was a dead raccoon. The old air-return ducts are made with just a sheet of metal to close off the space between two floor joists. The joists extend beyond the edge of the house to support the porch outside the front door. There were some little openings, enough to let the carcass smell get sucked in when the furnace ran.


  28. SKUNK SMELL odor in house, recommend you try the following remedy as we had the same issue for the past two weeks. We have a furnace room with a floor drain, we noticed that the smell was extremely strong in the furnace room so we smelt the floor drain and it reeked. My husband pored approximately 4 to 6 cups of water, then 4 – 5 table spoons of vegetable oil in the pee trap. (the oil prevents the water from evaporating from the pee trap).
    Today, came home the smell is gone from the furnace room and our house. This may or may not work for everyone’s smells, but thought i would share our remedy for our solution and issue.


  29. Thanks for all the suggestions. Last fall when we turned our furnace on there was a bad odor at first from the vent next to my chair in the living room. Nothing I tried helped for long then I started noticing it in other rooms too. Not a dead animal smell and not a sewer smell more like something soured, but the odor was not in the basement where the furnace is. I found this site and after reading the comments I did 2 things. First I changed the setting on our air purifier in the basement and second I poured drain cleaner in the sink and tub in the bathroom and before long the odor was gone!!! I never would have thought either would work and I imagine it was more the drains. Anyway, thank you!!!


  30. We have a smell coming from our heating vents that smell like dead rodent and mildew. It was overwhelming. We had our ductwork cleaned and they found 3 dead rats. The smell went away for a while. Now it smells like rusty, mildewy (for lack of a better word) left over dead rat. It’s not as bad as it was, but it’s still there. We’ve searched, and the company that did the duct work searched to no avail. We had a water filtrated filter system instead of the regular filters which they switched over to regluar filders. They also disconnected the “non-working” humidifier from the furnace. But the smell is still there. HELP!!!


  31. We have a SKUNK SMELL coming from our heating vents. This has happened for about 2 months from time to time. I don’t get it why it’s only happening every once in a while. Our unit is electric and we do not have any gas in the house. The unit is located in the attic. I was wondering if the skunk smell could actually be a smell the unit puts off when wiring is over heating or something else with the unit. It’s an over powering smell when it happens and takes days before it’s gone only to happen again a week or so later. Frustrated with this smell.


  32. We had a high efficiency furnace installed a few weeks ago and have the same problem. Weird skunky type of smell that comes out of all the registers. It is worst in the duct (that leads ot my bedroom) that is attached right on top of the furnace/AC stack. Furnace folks say it isn’t their furnace making the smell. Everyone can smell it, but nobody can say exactly what it is. I’m going nuts!


  33. Found your site after three months of frustration dealing with a dead animal smell that ONLY happened after we used the shower in our master bathroom. I checked everything – and I mean everything including our plumber checking all pipes, etc and our electrician checking wires. The smell only happened when we we took our morning showers. Finally, tonight I rechecked all trap doors, vents and pipe surrounds and lo and behold what did I find – 2 dead mice directly under the drain pipe from our shower. I think the problem is solved since the smell was probably triggered by the hot water running over the corpses of these two little critters. If that’s not the case I will repost. Otherwise adios and thanks for your help.


  34. If you have an p trap coming off of the cooling unit in your attic, be sure it has water in it. My new sysyem has a place between the unit and the trap to add water. This keeps odors from entering the forced air area. NO MORE SMELL!!


  35. We don’t have an electronic air filter my husband said. We have that same terrible odor. We built our house last year. I came home from vacation yesterday and walked in the house to this terrible odor. It is a smell like something dead or sewer. My husband poured water in the drain in the basement because we thought that might be the problem. But the smell is still here. Its been here a few days. Help!


  36. I have had an ongoing problem (over a year now) with a bad smell coming from my furnace return air vent (intake vent) after the furnace shuts off.

    I have an old wood burning fireplace in the living room upstairs (never been used by me). The solution has been to close the old wood burning fireplace vent. Right now, I have heavy duty plastic
    and duck take to seal off the fireplace. I will likely need to get my hands dirty and figure out how to close the vent properly. In the mean time, this has been working wonderfully for a week. (It lacks in appearance compared to my candle display inside the fireplace)

    Here are the details of the problem and things I have tried.

    The house was built in the 1920’s. It has 2 floors, no basement. The furnace room is located on the ground floor. The ground floor is fully renovated, it’s not smelly and there is no laundry room. (There is a 1bdr suite that I rent out.)

    The furnace room is small, it hosts the furnace and hot water taken. Both are natural gas. The furnace & hot water tank are vented into the chimney. The furnace is a Sears Kenmore (not a great brand of furnace I’ve been told), 12-15 yrs old. This furnace has an open vent – meaning that the gas burns – air flows up – then out, but it is not sealed, you can see an opening between the vent that goes into the chimney and the furnace. This I have been informed, is by design.

    The smell would come and go. I would describe it as fumes, other people had different descriptions. It was a very hard smell to explain and no one (a lot of people have given me their best guesses) could figure out exactly what the smell was.

    1) I had all the gas lines checked by the gas company. There were no problems.
    2) I had the vents cleaned & sanitized
    3) I had a chimney liner installed ($900+tax), it was initially thought that I ‘might’ have a negative air pressure problem, this was suppose to fix it. No change! (As it turns out I do believe I had a negative air pressure problem)
    4) I already had an intake vent from the outside directly connected to the furnace intake vent (or return air line) in the furnace room. By one of the repair men: This was removed and placed beside the furnace (not connected to anything, just a pipe that runs directly into the furnace room from the outside). This actually made the problem worse.

    In the end, 3 different furnace repair companies could not figure it out. We were all perplexed!

    My Trial & Error, What made the problem better or worse.
    – I would open the windows downstairs (upstairs windows were closed) and it would make the problem worse. (At the time it was spring, I was painting downstairs and wanted to let it air out)
    – This led me to many more tests, of opening and closing things. In the end, I figured out that closing all the windows downstairs and closing the door of the furnace room, made the smell less of a problem. The more air that was allowed to enter the furnace room the worst it got. The furnace repair men all gave me a hard time about this, because the furnace needs oxygen to work correctly.

    I was convinced that it was a negative air pressure or air flow problem. Air would flow back out of the intake vent after the furnace shuts off and there is the smell. If I could stop the air from flowing back, the smell would go away. I finally discovered that air was flowing into the fireplace, up & out the chimney. Hold a lighter near the fireplace and the flame would bend. When I first put a plastic bag up to the fireplace, it sucked right against the skirt. Sealing the fireplace I believe has stopped the upstairs from loosing so much air, and stopped the need to suck air in from the downstairs.

    The smell was coming from somewhere and what exactly the smell was is still a mystery. I believe it was sucking air back in from the chimney.


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