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 :-)

252 thoughts on “Revenge of the Smelly Ducting

  1. John, can it be a ‘sewer, or sceptic tank’ smell being moved by the wind that day. My daugther had a smell and a wet basement wall that tricked us for a year. Finally figured out the sewer line was cracked inside the basement wall. No leak inside or outside, but in the wall. Just a thought. It would seem however that a H/C guy probably already eliminated that prospect. Ours wasn’t a true sewer smell because the water we were dealing with could probably only be classified as grey water.(leak was small enough not to allow any solids to escape into the wall.) c

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  2. Some things to check

    1. Air intake for furnace (should be one leading to outside) is clear and no smell near it outside
    2. Furnace filter is cleaned/replaced and put in correct orientation
    3. could have ductwork cleaned out (can DIY a bit by using a shopvac to clean out first three/four feet at each vent in each room)
    4. no cat litter pan or anything like that in basement or near cold air return vents
    5. cold air return ductwork is clean
    6. cold air return vents cleaned out and working properly

    If you have a forced-air furnace, consider that when the furnace comes on, it sucks down a lot of air and moves it around so…

    You may need to check for mold/mildew. Does your laundry dryer vent properly outside? (if you vent inside, the moisture can cause mold buildup) While you’re checking your dryer, if your hose is more than a few years old, replace with a clean metal one.

    Have you looked in your attic? Check for dead animals, mold, etc. And while you’re up there, see if you have enough insulation! (you can then run your furnace less)

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  3. Our furnace is in the basement, and the cold air return goes from a room where we’ve never noticed the smell — and we haven’t noticed the smell in the basement, either (until yesterday, but even then, not in the utility room). I’ve also stuck my nose into the attic and our crawlspace and haven’t detected anything.

    I too have wondered about the ducts, or maybe the heat exchanger. We first noticed the problem on a warm (for late winter) and humid day, which was nicely situated between cold spells… wouldn’t surprise me if we got some condensation somewhere.

    I suppose it could be a sewer or septic smell, originating from somewhere other than the utility room or crawlspace. Hmm. I’ll have to mention that.

    Thanks!

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  4. I too, have that smell in a 3 yr old house we have just purchased, no heat running, and the oder comes and goes, thinking maybe dead animal in the duct work,

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    jgoerzen Reply:

    Ours eventually disappeared over time… the people we talked to thought it probably wasn’t a dead animal because the smell lingered so long. We never did figure out what it was.

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    DMW Reply:

    Just in the last two months I have found an odd smell in my cold air return. My furnace is not even a year old and I did not notice a smell during last winter or spring/summer. It is driving me crazy and I am making my husband crazy by having him remove vents and look for something dead. No plumbing near the vents so I, too, am at a lost!

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    Anonymous Reply:

    turn off your electronic air cleaner on the furnace- worked immediately for us

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  5. Did you ever figure out what it was? We just started noticing a very similar thing this last week and we are pulling our hair out. Has anybody reading this ever solved the problem or figured out what”it” was???? Thanks!

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    jgoerzen Reply:

    Nope, we never figured it out. It slowly disappeared over time. Very, very strange!

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    Anonymous Reply:

    Sniff around – particularly near the drains in the basement to see where the smell is coming from. If you have a basement that has a drain, the smell could be coming from the drain and spreading to the rest of the house when the furnace fan turns on. The smell could be coming out of the drain since the trap may be dry. Pour a gallon of water into the drain and see if that prevents the smell from getting into the basement.

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  6. I don’t know if you ever figured the odor out but we bought a new house and had the same problem. Finally we found out it is coming from the electronic air filter on our furnace. We turned it off and the smell went away. Thank God– it was driving me crazy

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    Bill Reply:

    Sound similar to a problem I’ trying to figure. Everytime someone takes a long shower a sudden burst of foul air comes through the cold air vent inside the living room. Anyone have an idea?

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    Anonymous Reply:

    We are having a similar problem. Every time we shower and use hotwater and kick our furnace on it creates a very foul sewer smell. Noticed it coming from the ducts, so I tracked it to the basement. I noticed that it was coming from a non-caulked hole where my air intake and exhaust exits the house. Above that area is a screened porch with a tile floor. The exhaust and intake travels the length of the screened porch and comes out in the open air. The other area that wasn’t caulked was drawing air becasue out hot tankless water heater was drawing air from the outside (tight house) to feed it. Well, our setic tank sits about 8 feet from the edge of the porch and we are thinking that the gas from the tank is escaping, getting trapped under the porch and when the heat kicks on it draws it into the house. Can’t smell it outside, but you can tell it is coming from the outside. We caulked this area and the smell stopped. Found another area I need to caulk tonight to stop it there too. Hope this helps. It’s a really strange occurence. House is only six months old. I’m going to have the HVAC guys run another air intake into the furnace room where the tankless water heater is. This should the allow the water heater to suck air from that pipe run to a more open area outside (fresh air), rather than sucking the trapped gas under the porch through small cracks in the walls under it.

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  7. I am having the same problem. Please let me know what you come up with because it is so weird.

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    jgoerzen Reply:

    We never found the problem — it just disappeared after awhile.

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    Anonymous Reply:

    How long is ” a while”? We are wondering how long we will have to live with the smell!

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  8. We just went through this over the weekend. Not sure if yours is the same problem, but we noticed this horrible smell for a few days, but it just suddenly got worse one day. It seemed to emanate from the basement in the laundry room. We checked ducts, drains, the works, and finally we found it! It was a dead animal of some kind in our dryer hose that vents to the outside! The flap cover had broken long ago and I guess this little animal wanted to get warm. It was a nasty gross mess, including some maggots and potato bugs ACK! We cleaned out the dryer and replaced the vent cover and dryer hose. It’s been 2 days now and the smell is finally going away. Check your dryer hose, and the flap cover to the outside….maybe you’ll get lucky with that. Hope you find your problem

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  9. I have been having a problem with smell off and on for over a year. It doesn’t matter if it is hot or cold, heater running or not. Seems to be comming from heater vent. Nothing in crawl space that I can see. ANY suggestions???

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    Kelly Reply:

    We have a smell that sounds like yours. It is such a foul smell that it really defies explanation. It is like a dead rat (which we have a big problem with), with a little musty odor and skunk type smells all rolled together. It is just awful. We just purchased our house and haven’t been in it more than 3 weeks and I am going crazy with this smell. I haven’t called any experts in yet – but I am going to. The smell is coming from 2 floor vents in our house. The heating system is really old – I am wanting to just rip out the whole thing. Any suggestions would be helpful!

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  10. ELECTRONIC AIR FILTER: someone mentioned this as the problem and solution. We have had this problem too. We have two systems in our old house and the electronic air filters are the cause. I dont know why. But turn them off and the smell is gone the next day. I think it has to do with the level of humidity in the air. When it is more humid the filter generates this smell. In our case it wasn’t a maybe – it was the problem. Every once and a while I clean them and put them back on and eventually the smell comes back. They sit off and were a waste of money.

    Good luck.

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  11. If anyone could help me I would sure appreciate it. Feel free to e-mail me. I have a dead animal odor coming from my heating vents and the furnace isn’t even on. It’s putrid. I just spent 330 dollars having all my ductwork cleaned and sanitized and two days later the smell is back. When it came back very suddenly today, I noticed the side of my furnace where there is an air vent really stunk. I took off the vent and the smell just emanated from somewhere in the furnace. (or so it seems) I have also worried that it is some sewage problem although I don’t have septic and it does seem to come from the furnace area. I have had to block all my heating vents with cardboard. The smell goes away once the heat has been on a while, but returns as soon as heat is off.
    I’d appreciate any thoughts.

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    Olga Reply:

    Linda – I read your comment and we are in the exact same scenario. I spent 400 bucks today having the ducts cleaned and now I’m still smelling that terrible smell. Did anyone reply to your question? have you gotten rid of the smell? One other thing that I’ve noticed is that the smell only comes when the temps outside are cold (below 50 degrees). Perhaps the cold air is somehow pushing the smell around? My husband and I are very upset, since we love everything about this house (just purchased 2 months ago) but we can’t stand the smell! HELP!

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    Sam Reply:

    Did you figure this out? We have a similar problem, cold mornings, a sweet smell comes out of the main intake vent in our bedroom..

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  12. We have been having the same problem. We just moved into our 150+ year old house(it was rehabbed) 2 1/2 months ago. The first month we didn’t have any problems. Now anytime we run the shower, this sewage/marshy smell comes through the vents. We had a septic guy look at the septic system and not finding any obvious cause, he thought a second vent would help…well it didn’t. We are thinking about getting a plumber in here next. We also had a dead animal smell coming out of the hole in the wall for the hot and cold water pipes leading from the basement into the kitchen when we ran the washing machine. We filled the hole up with expanding foam and that seemed to have helped. Running the sinks and the toilet haven’t caused the smell yet all the water goes down the same pipe out to the septic tank. It is strange
    annoying and embarassing. We are desperate to get it to stop. This is our first home and we really want to love it, but right now it’s hard to not be frustrated.

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  13. Help! I have a related problem. Last week, I found out that my apartment furnace was emitting 600ppm of CO. So I had the furnace replaced with a brand new furnace, with new ducts, fixtures and all. A few hours later, there is this smell which is hard to define. A mixture of skunk or dead animal type smell which is lightly suffocating and highly discomforting. There is no blurring of the eyes with this smell. I am sure that there is no gas or CO leak since furnace was totally replaced. Also smell emanates from the vents. Area around the furnace itself has no smell.
    Thanks in advance for any advice on resolving this issue.

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    Donna Williams Reply:

    I would like to share with you our battle with our illusive smell from our basement. Our home is 17 yrs. old and is not using a septic sys. Our smell is a cross between sewage & sewer gas smell, musty water and ???). A good plumber recently replaced two toilets on main level, both had faulty seals. But the smell came back-! Replacing toilet seals is relatively cheap and easy and is a good idea as sewer gas can escape from beneath a bad toilet seal and sink into the basement (so I have been told). We have replaced our hot water heater, thinking the anode rod was corroded. The smell came back. We have repaired our water main into the house (cracked off INSIDE the basement foundation approx. 2 years ago). Smell came back-!! NEXT WEEK, we are having our dryer vent checked. Thanks to your comments, I have learned there is a real possibility that something met it’s death inside my dryer vent, which is many many feet too long, installed incorrectly with bends and twists that very possibly are holding massive amounts of soggy dryer gunk and Lord knows what else. I will now turn OFF my electric air cleaner. It’s a process of elinination I am learning. Our plumber is coming back after the dryer vent is cleaned and checked and will (hopefully) do a smoke test, where the smoke bomb is dropped thru the stack on the roof to identify leaks. Smoke bombs like this are apparantly hard to find here in Chicago (short shelf life) and I am hoping he does manage to get his hands on one. Thanks for the sharing of ideas, I too will pass along our finding on the road to eliminate the STINK!

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  14. I have spent the whole day smelling this f’ing smell in the basement and its exactly what u guys are describing…Having no smell from the vent or toliets or anything…but I noticed its comeing from the corner of the cealing…We took off the plug in and it smelt like skunk..any sudgestions? I do believe its a dead rat or something….we are probably going to rip off some dry wall and find the problem….

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  15. hello, we too have an odor that has just recently begun 3 or 4 days ago. woke us out of a sound sleep. but in our case it seems stronger when the furnace is running. is this a different problem?

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    Teri Reply:

    I am having the same problem. I am seriously considering turning my furnace off and buy electric heaters for every room! The smell was bad about 2 months ago. Then it went away completely. Now it’s back with a vengance! You can smell it all the time but when the heat is on it gets 10 times worse. I have seen posts saying to turn off the electronic air filter . . . would this be a switch that is on the wall? I have a switch that is in the “on” position but I don’t know what it is for. Any help, I will be forever grateful!

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  16. HELP!!! My husband removed the vents to install these scented vent paks, but upon doing so he cursed us with this FOUL ODOR!! We had the ducts cleaned and deodorized. It worked for a while but now he removed the ceiling fan to replace it and now IT’S BACK. It smells like an animal rolled in standing water. Please help me.

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  17. I get this same problem every year when it gets cold. I suspect that it is a downdraft from my furnace. I do not have a combustion air intake because it can draw enough air from the basement. I think as it is running it creates a negative pressure in my basement. After it stops, the negative pressure draws air from the roof vent back into the house. My plumbing stack vent is a little lower than my furnace vent on the roof. I think the cold outside air is trapping the warm plumbing vent air and keeping it close to the roof. If anyone has had this similar problem, have you had to install a separate combustion air intake? I have seen a product that is a charcoal plumbing vent filter that is supposed to eliminate vent odors. Has anyone had any luck with this?

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  18. Check to see if your condensate drain from your A coil in your Air handler is installed properly. if it is not the sewer gas can come back up that drain pipe right into your ductwork.

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  19. Even if the drain is installed properly in the winter time there is less humidity and the p-trap could dry out and let sewer gas by. Try draining it outside independant of the drain system.

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  20. Someone from this site e-mailed us directly re: a post we left in 2005. We sure did find out what is was! Not one, not two, not three, but 4 DEAD SQUIRRELS! 3 had buried themselves deeply in the attic insulation and even under some duct work (it was tricky and very gross to retrieve and dispose of them, and my husband deserves high praise for doing so). The other was under our crawl space. It was right after a hurricane and we figure the squirrels came in looking for shelter. We had 3 again this year so as soon as we noted the smell, we searched and found. I urge all of you with this issue to look for dead animals in your insulation and crawl space. jt

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    ethel wright Reply:

    i have this putrid odor coming into one bathroom, you cant tell if its from the heating vent or the drains , plumber has been in three days in a row ,i have spent almost $4,000. no animal yet found.,or just were this stench is coming from,i will have the men search in the attic, most of the septic tank pipes have been replaced in the crawl space out thru the wall thanks for sharing your info with us

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  21. I need help with a smell that is plagueing us 24 hours a day, 7 days a week, warm or cold weather.

    It’s definately sewer but it’s comming form our heater vents. We both this house just recently and have been in it for about 4 and a half months, and the smell is enough to make not only us, but anyone that comes over gag.

    The heater ducts weren’t even sealed, only nailed to the sides with large gapeing holes, which I have sealed off. However, the Electric Furnice stinks, the smell comes from up under the house, in every room…the kitchen, living room, all four bedrooms and both bathrooms. There is no “apparent” sewer leak that can be seen…

    Please help. We have been trying to get someone to go under the house, but no one will, as there is some sort of standing “liquid”, and we were advised not to go under the house untill summer…but we can’t live like this.

    I’ve contacted my agent, the previous owners agent, the city, the county, plumbers, heating companies, etc…

    I’m at a dead end. :(
    Thank you to all that respond.

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  22. We had this problem a few years ago, in my boys bathroom. We had people come and check out our vents and said they were clean and no holes. My boys were little and had potty trained the two years before, so I figured well maybe it was the wall behind the toilet. They don’t always hit their target. :) So, I decided to tear out the wall and put in tile. That way it would be easier to clean. When I began to tear out the wall, I realized I was going to have to take out the tub also. Anyway, mice had gotton into the walls and were under the tub. They brought with them dog poo, dried mushrooms and other things. The mice were rotting in the walls. It was so gross! Under the tub and in the walls was where the smell was coming from. We had to tear out all of the walls in the bathroom, and redo the whole thing. The smell went away. Our house was only a few years old then, that was several years ago. There was no obvious spot that we could see that they were getting in, we checked all over for holes. We now have the problem again, and now I not only have sheet rock to take out , but tile! Here we go again. Good luck!

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  23. Hello! Previously when our furnace has clicked to turn on but no air is blowing out, a foul urine smell develops in our house. I don’t know what may cause this, however we do have a mold issue downstairs. So if you have any suggestions of what I should do that would be great! I am scared that this will cost a lot of money, in which I dont have!

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  24. Help! My house stinks at first it was in the back hall this funky smell now it’s everywhere. It seems to be comming up threw the heater vents all over the house. My husband checked for dead critters and found none. NEw house we built only a 1year old….Need advice before I go crazy…

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    jeaniek Reply:

    we had the same new home problem. after ripping apart all the basement ductwork, we accidently found our drain pipe from the common bathroom wasn’t sealed when the builder installed it. th pvc pipe was next to a cold air duct which sucked sewer gas into our hallway and master bedroom. once my husband sealed it the smell was gone!

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    Dave Reply:

    We noticed a horrible smell in the house and it was only getting worse. I went around the house smelling each vent and found one that smelled more potent than the others. I called a few duct cleaning people and they recommended getting a pest control specialist to come out and look around first. I called a few and never got a call back so I decided today to go in myself. They weren’t kidding about the “crawl” space, this not a place to go if you are claustrophobic. I made my way back to the corner where the nasty vent was. Right away I noticed that the insulation was hanging down in that area. I pulled down the piece closest to the vent and a dead rat fell out along with a few weeks worth of poo. The smell could have knocked a maggot off a S**T pile from 100 yards. It was down right nasty, but the smell is gone and feeling that I had just saved a butt load of money made it even better. I was really surprised how something outside the duct work could make its way in. We smelled it all through the house, but in the end it all came from that small area. Hope this helps somebody.

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  25. I’ve just had this problem today, a strange smell from the closet that goes down to my basement. First I thought it was from the shoe boxes we had, but as I got closer to the basement underground door the smell got worse. I’m pretty sure the smell is from the basement which I’m afraid to go in now. I also smell it slightly from the bathroom next to the closet, also in my garage near the heaters, but these locations the smell is not as strong.

    A few months ago I’ve seen a small rat running through my garage and outside of my house, and I do believe they’ve made my basement their nest. If my prediction is right, the rat probably found a hole near the heater and went down into my basement, since and stayed there for the heat.

    My second thought on this problem is a sewage pipe leak? and a backup of stinky gas. From just the smell of the odor I cannot tell if its a backup gas or is it a rotten meat/dead rat smell… cause honestly I’ve never smelled either. So I have no clue which one it could be. Right now the house smells fine as long as i dont open that closet… But I’m calling the pest control to find out the problem. Anyone know how much it might be? If it’s over 200 dollars I might just do it myself. But hopefully it’s not.

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  26. We have had a stinky problem for months now. It’s really strong when running the washer and the furnace is on. We’ve checked everything with the washer, that’s not it. Today I was cleaning out the floor heating registers and found water standing in one of them! The smell just about made me pass out! This register is on the other side of a bathroom that we do not use. (Toilet backs up into shower, but that’s another problem). So, my guess is when the washer drains it is getting in this duct, and the air from the furnace is making the smell worse. How do I go about finding out where the leak is?

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  27. My wife and I have been enduring a smell for 2 years since we bought a Sears Historic Home, aka money pit. I just read a bunch of the emails on this page and I now realize I am not crazy. Trying to describe the smell and find out where its coming from is the most frustrating thing I have ever endured. Im so ready to be done with this that I would eat a dead rat in slow-motion if that would make my smell go away. I dont have the energy to type my saga because Im out of energy. For god sakes, cant plumbers figure this s**t out. Ive had 4 plumbers and all of them are baffled. My condolences to you all!

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  28. We live in a condo building that was reahabed 2 years ago. Everyone in the building has the same washer and dryer but we seem to be the only ones with the smell. And it seems to be coming from our inside our washing machine. It is exactly the smell everyone is describing which is wet animal/musty/moldy. Miraculously our clothes don’t smell. I notice that it is worse when it is really cold outside and we just over a really cold snap here in Chicago. Occasionally it travels through the condo but for the most part it stays by the washing machine, which is located in our hallway. Any suggestions?

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  29. We’re going on our 3rd year of intermittant sewer smell in one corner of our finished basement. We’ve checked the drains, but the smells strongest right when you get down the steps. There’s just a wall there–it’s the edge of our basement. Every year, in the fall, we think the smell goes away… and maybe it won’t come back. But then every spring it’s back again.

    This is roughly when we stop using the heater during the day (though the nights have still been cold lately).

    The basement was finished when we moved in, so we’re hesitant to start ripping up carpet or tearing down walls.

    We thought it might be something dead, but it only happens in the spring/summer.

    Anyone have any ideas?

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  30. UPDATE: So we tore up some carpet last night and found…

    a bunch of cracks all leading to a concrete-filled drain!

    The cracks smell so we think it’s the dried up drain, leaking sewer gas through the cracks.

    Not sure how we’re going to fix it yet, but at least we think we’ve found the problem!

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  31. Makes no sense… We have a similar problem, skunky smell that comes and goes, but only on the second floor. No easy way for skunks to get into attic, it’s 2 stories up.

    The smell comes and goes… you’ll walk and catch a whiff of it but can’t really tell where it’s coming from.

    Not the heating vents – we have hot water radiators… and the smell has been in the summer and winter.

    it’s very odd…

    Reply

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