Cold-weather-related sewer or septic system odors:
This article describes how to diagnose and correct sewer gas or septic odors (and other building smells and odors with focus on diagnosing odor sources and causes in cold weather. This article on diagnosing sewer gas or septic odors is a special cold-weather edition of our more general advice on finding and curing sewage odor problems.
Here we focus on sewage or septic odor problems that occur during cold weather or wet weather.
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Where on the property are odors strongest? you may be able to point to a waste line, building exit piping, leaks at a septic tank, drainfield failure, or even a neighbor's septic system problem.
Look for a wet area, possibly covered by snow in northern climates - kick the snow aside in a grid pattern over the septic system components (don't' fall into a collapsing septic system - it can be fatal).
Look for areas where snow has melted to a thinner cover. This can occur in a normal system (bacterial action in the soil over the septic system and warm septic effluent carry heat out of the septic tank). But it can also be a clue of sewage effluent coming to the surface. Check such areas for effluent.
If a waste line is blocked or partly blocked and the odors are near the house, such as at the house wall at the waste line exit point, effluent could be running along the buried pipe but outside it, having leaked from a damaged pipe at the wall, between the wall and the septic tank, or at the tank itself there could be an effluent leak where the line enters the tank, or at the tank cleanout top cover (which would indicate a blocked tank outlet or blocked drainfield).
Effluent will follow a buried pipe because it runs in a trench dug in the soil - the pipe and backfill in the trench are less solidly packed than in the surrounding soil - the trench acts as a conduit to bring sewage effluent to the house if the trench is filling with liquid.
At left we show a broken sewer pipe found by lifting a section of sidewalk in a soft smelly area of the yard.
At a different property where basement paneling was removed following "a history of basement water entry from 'rising ground water' (according to the basement de-watering company)" a company had installed an expensive interior trench and drain system and sump pump to pump the "ground water" away.
We saw an inverted "vee" of leak stains on the basemen wall extending from below the main waste line where it exited the building.
It was obvious that the water entry had been not from rising ground water but from a broken leaking waste line outside the wall. Sure enough, our septic dye appeared in the new basement trench and drain system in just a few minutes.
The basement de-watering system had not been needed at this home, and the owner still needed to have the broken waste line excavated and repaired.
Look for leaks at a waste line, perhaps first by having a plumber snake the line from inside the building to see if s/he feels evidence of a broken or collapsing or damaged pipe between the house and the septic tank.
See How to Find Distance to Drain Blockage
If the drain field is saturated or blocked, expect to find abnormally high sewage level in the septic tank, possibly even backing up and flowing out when the tank is opened, and possibly also evident at the distribution box.
See SEPTIC TANK INSPECTION PROCEDURE
Sewer gases occurring in wet weather:
Any of the following articles will offer helpful suggestions for finding the source of odors that seem to appear only in wet or cold weather:
This topic has moved to PLUMBING VENT BLOCKAGE ODORS - separate article
This discussion is now at TRAP SIPHONAGE & SEWER GAS
This topic moved to TRACK DOWN COLD WEATHER SEWER ODORS - separate article
Please see SEWAGE ODOR SOURCE LOCATION - other Sources of Sewer Gas or Methane Gas Odors in buildings
Continue reading at SEWER GAS ODOR REMEDIES or select a topic from the More Reading links or topic ARTICLE INDEX shown below.
Or see WET WEATHER SEWER ODORS
Or see TRACK SEPTIC ODORS to SOURCE - weather independent
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our whole section of town often smells of sewer gas! it is noticeable for 2 or 3 blocks. what's up with that? p.s. - most often is worse when it cools down after a warm day or during the monsoons.. - Sharon 7/22/11
Sharon when there is a sewer odor in the neighborhood, if your homes are on private septic systems I suspect someone's drainfield is in failure. If we're talking about a community where every home is connected to a municipal sewer, there could be a burst line, effluent breakout, a problem with a pumping station, or the odor could be from something else.
I would like an opinion. I have a cesspool, it has been pumped out even though the gentleman said it did not need it. Every time we have heavy rains in our area I get a foul smell inside my home;. when the rain stops the odor goes away. I had it pumped thinking that was it but the cesspool man said it was not Can you give me any idea of what it might be the system was installed in 1964 and even though old still works perfectly with this one exception. Thank you - Carol 8/15/11
Possibly your plumbing vent system is not working properly and/or there are downdrafts from a plumbing vent into or around the home in wet weather;
More likely the cesspool is flooding and forcing sewer gases back into the home, perhaps leaking out around toilet seals or from un-vented or poorly-vented sink or tub traps.
Rain could be flooding the cesspool, causing a breakout of septic effluent and odors - more likely if that were the case the odors would be strongest outdoors at the cesspool; It would be stunning if there were a 1964 cesspool that was still working. In what part of the country/world are you located - what soil conditions?
We moved into a doublewide in western NC last March. We noticed, mostly late evenings and early mornings, a really bad sewer smell. Our landlords said that sometimes, as a system gets used to new people and new system uses, it can be a little smelly. Anyway, soon, spring and then summer arrived and the smell had gone away completely.
At the very first sign of fall, however, the smell has returned. Now that all of our nights are in the 40's or below, we are smelling it again every morning and evening, but not during the heat of the day when temps reach the 70's. There is no smell coming from inside the house, only what drifts in through open windows. Everything seems to drain fine in the house. Totally clueless and really frustrated at this point. - Jeff 10/6/11
That's a new one on me - I don't think septic tanks and drainfields know who is using the system. There might of course be a difference in the level of usage - if the new occupants are using more water or if there are more occupants than previously, that may be causing a septic failure to show up. The fact that you smell odors outside only sounds as if there may be a failing septic drainfield.
I hope that some help be given as we are at our wits end. I have and unfinished bathroom in the basement
and we are haven s sewer smell that is very prominent in the unfinished bathroom. Could this smell be coming from were the fixtures are plumbed but not in stalled I would love some feed back as we are so confused on what to do - Laila 10/20/11
I'm not sure what is the state of affairs in the new bathroom, but here are some possible reasons you'd smell sewer gas there:
1. If you have an open drain line without a trap, such as a mount for a toilet, sewer gases would come out there - use a rubber plug or a large rag to stuff that opening until a toilet is ready to install. Don't let the rag or opening-closer fall down into and clog the pipe however.
2. If you have fixtures like a sink or tub or shower that are installed and have plumbing traps but they have never been used, the trap will be dry and sewer gases can come out at those points. Just pour some water into each trap to form a seal. A cup or two will be plenty. If you are not going to use the fixtures anytime soon you can pour in clean mineral oil instead.
3. If fixtures were installed improperly you could have a leaky toilet wax ring seal
4. If the plumbing was amateur or incomplete you could be missing a plumbing vent connection or the plumbing vent piping could be incomplete, disconnected, or leaky.
Keep us posted - what you report will help other readers.
Ok I have an issue... I own a bi-level home. One of the bedrooms is in the lower level. The entire lower level is finished. There is a french drain that run around the entire basement, however most of it is covered. There is no water, nor has there ever been any water in the drain. Over the past week, out of the blue the odor that is coming from the drain is mind blowing. It smells like ammonia and other things. The room that smells is closest to the septic tank. Thinking that there might be a problem I had the tank emptied and still no relief from the smell... When it rains the smell only gets worse... Any suggestions on what I might be looking at. - Brian D 11/29/11
Brian, on occasion I've found that a leak in the sewer line or even at the tank itself it it's near the house can leak into the foundation drain or perimeter drain and even enter the basement. As you've not seen a problem at the tank itself I'd check the condition of the sewer line between the house and the septic tank next.
Also, if the building's vent system has become clogged (animal, insects, etc) that could be a source of local smells.
I read your article and I would like to explain my problem to see if I have come up with the problem. I live in Cheyenne Wyoming and when it is very cold (below 25 degrees Far.) we get a very strong raw sewage odor from our basement bathroom. I have narrowed it down to the bathtub. We did not finish the basement, it was finished when we moved in. The odor was not disclosed to us when we moved in 3 years ago and this winter it is worse but it is colder. We have smelled it every winter since we moved in. Now tonight I decided to try an experiment. I closed the drain on the tub and put water in the tub and this seemed to fix the problem. So my opinion is that they did not put a "P" trap on the tub. So what do you think?
I do not smell the odor from the sink, the toilet, or the floor drains.
Thank you - John 12/6/11
There may be a corroded leaky P-trap that thus doesn't maintain its water seal. Try pouring water into the trap and inspect with a good light to see if it remains in the drain; Unfortunately some demo and digging may be in order to fix this odor source.
Our septic tank is located under our garage we have a sealed hole with a cap on it during the cold months we get a sewer smell in specifically one part of our bathroom its the area where all the pipes are located the toilet shower and sink water all go into the septic tank we tore up our floor and replaced all the pipes we had our tank checked its working fine not much in it but as soon as it got cold it started to smell do you have any ideas what we could do - Cheri 1/14/12
oh why do people type in all caps.
A septic tank under a garage floor sounds like a bad idea to start with - but in any case if it smells the system may be backing up; check for drainfield flooding;
Watch out: accumulated sewer gases indoors (in your garage) can cause an explosion or can be an asphyxiation hazard - i.e. fatal
I have a septic system that works fine, however I have an unpleasant odor. ..usually when its cold and/or damp outside. I originally had a single wide mobile home then moved it out and put in a double wide....that's when the problems started. I've tried everything with no luck. I've tried suggestions from plumbers, had plumbers out and no one can narrow down what the problem is.
When the double wide was installed the plumber put in a clean out trap....could that be part of the problem? I had the tank pumped in the summer and it seemed to help....but not get rid of the problem. I'm now trying to sell my house, but can't sell until this issue is resolved. Please can you offer any suggestions for me.?
Oh...in the tub and at bathroom and kitchen sinks there are those stink pipes (?) with vented tops ....I've put new ones on all sinks. It helped a bit but didn't solve the problem. The shower in the master bath (the drain holds water) seems to harbor a bad bad odor. I'm at my wits end. - Linda 2/8/12
When you changed your mobile home, is it possible that someone drove across and crushed a septic drain line or damaged the drainfield?
After a change in weather to cooler temperatures, we are smelling sewer gas which we believe are coming from both bathrooms. My husband says the bathrooms are on separate ends of the house. The smell of gas is throughout the house. - Gail Gilbert 9/10/12
Gail, check the odor track down suggestions above
My furnace in my mobile home sits in front of a lot of my plumbing in the bathroom. i believe because as the weather gets colder, we use the furnace, and then that's when it smells the worst. i have also noticed that while the furnace is running and then run water in the kitchen, its the worst! - Anon 10/31/12
Look for a blocked or missing plumbing vent that is causing drain gases to back up out of a drain near the furnace return air intake
Last may I installed a washer in the basement. Everything has been fine until we had over 6 inches of rain during a 24 hour period back in September - at that time, I noticed a septic odor in the basement and also in the cabin. Since then, the odor has appeared during cold damp weather, but only in the basement. I don't smell anything outside, just in the basement. My tank was cleaned out four years ago and I live alone, so I would think the tank is fine. Before calling the septic service and spending money I don't have to spare, I would appreciate your opinion and suggestions. - Diane 10/31/12
Check our suggestions about bad plumbing vents as well as flooding septic systems in the sewer gas odor article links found at page top
Now that the weather has turned cooler and the furnace is on, we are experience sewer smells thru the heating floor vents on the upper levels of the house. We also have smelled the same odor from the drain in the basement bathtub. There was no odor throughout the summer or spring months. Can't figure it out so far. - Deborah 11/17/12
Deborah, if sewer gas odors come out of heating supply registers I suspect that sewer gas is being drawn in at a cold air return. That may help you start looking.
We can smell the same smell in the cold air return by our front door main level but we have very few cold air returns in this house. There is none in the basement bathroom and we have never isolated a smell from the furnace room. We did get a smell in the upstairs bathroom although that seems somewhat abated after we have constantly poured vinegar and hot water and bleach down all drains for the last week.
Last winter we had $10,000 worth of drain work done to replace the old clay ones under out house. They put in all new clean outs to meet regulations. This was done in December and we survived the winter season without any problem with sewage smells, although it was fairly mild. Prior to this work being done our daughter lived in the basement for at least 10 years without problem.
We called the drainage company who did the work back and he checked all the drains for P traps and dry/wetness. He claimed all was fine. Could it be the old city pipes coming into our new connection that might be a problem? Thanks for any and all help. We are in the process of getting someone to climb our roof to check the stack for some kind of animal blockage (nest) perhaps. It's driving us crazy. The contractor said to call him back if the smell still persists which we will do. - Deborah 12/5/12
I just can't hazard much of a guess at this point; I think the next approach is to use someone as a "smeller" who spends some time away from the site so that their sense of smell is fresh, then comes to the home and walks the outdoor site first, starting at the edges of the property and spiraling in towards the home to see if s/he can spot the source of strongest odor.
A similar approach can be taken using a TIF8800 combustible gas detector provided that you initialize it well away from the suspected odor source or property. See TIF 8800 GAS DETECTOR for details about this instrument. Many home inspectors have them as do some plumbing inspectors;
I also agree with the use of checking for vent blockage or vent piping leaks; typically if the plumbing vent were actually blocked your drains would gurgle when draining.
I am pretty much at my wits end with the sewer gas smell that enters the mail level of my home when the temp outside goes below 30 degrees. It is very upsetting because the smell is not pleasant and is most pungent near the kitchen window. The smell continues along that same wall into our living room and family room. My husband already went up on the roof to pour a gallon of bleach and then several gallons of water down the vent pipe. Nothing changed. Also, we had a plumbing service come out and no resolution there either. Help please. - S.N. 12/6/2013
Please first check out the article above on this page; let me know what questions remain and what has been done or checked so far and we'll pursue specific details for your home.
I did read your article through before sending you my question. The only addition is that we had another plumber out again yesterday and he was very perplexed by our situation. He suggested that we first put a turbine exhaust fan over our roof plumbing stack. He thinks that will help pull the air through. If that does not work, he wants us to apply heated tape to the pipe in the attic leading to the roof plumbing stack. If we do that, we will need to add in an electrical outlet in the attic to plug in the heated tape. Honestly, we are not too sure what to do. Your advice would be greatly appreciated. - S.N.
The added detail in your note lets me comment further with some diagnostic suggestions: While we might on occasion apply a band-aid to a problem as a temporary fix, generally it is better to find the cause of the plumbing problem instead. If the house is old and the odor problem is new, then the best approach is to determine what has changed or broken or come disconnected or blocked so as to cause the odor.
Adding a fix atop an existing problem without understanding the problem cause risks wasting time and money and risks failing to attend something important but not immediately obvious. Put another way, we can spin our wheels applying one band-aid after another without any success because we never took time to figure out what's wrong. Therefore
If a vent is becoming frost-blocked, the best repair is to remove the small-diameter vent and replace it with a larger diameter vent pipe. The location where this problem is most likely to occur is in a smaller-diameter plumbing vent, typically one that serves only sink drains such as a vent that only serves a kitchen.
If a vent is blocked for any reason (frost, or a frog as is in one of my photos), the result is not just slow drains and drain noises. If the vent is blocked some plumbing drains may siphon water out of the drain trap at the fixture (typically sinks or tubs). The result is sewer gas (smelly and explosive) entering the building at the drain trap. This siphoning is more likely if a building fixture drain is served by an "S" trap rather than a modern "P" trap. Check your kitchen sink and let me know what type of trap you see. (TRAPS on PLUMBING FIXTURES)
On many buildings, especially older homes, there are multiple vent pipes that protrude through the roof, serving different building areas; those serving full bathrooms are usually larger. At PLUMBING VENT DEFINITIONS & CODES we give tables of vent size requirements. Take a look and let me know how that compares with your home.
IF an on-roof inspection confirms that a vent is frost clogged then a temporary fix is to add a heating tape - you can run a heavy duty extension cord to avoid adding permanent wiring if you like, waiting for better weather to correct the problem properly with a larger diameter vent.
As we don't enjoy climbing ladders and peering into vents in winter - it can be dangerous if we slip and fall, while that's the most reliable diagnostic, how else might we guess that frost is blocking a plumbing vent? Long hot showers or dishwashers or running hot water down a drain can send lots of moisture up into the vent system; if we notice that drains are slow and noisy or odors are worse an hour or so after such fixture use during freezing weather, that's suggestive of frost clogging.
We could also try warming a heating vent from inside the attic, using a simple hair dryer - though quite a bit of warming might be needed to thaw the vent portion that extends outside above the roof.
Borrowing from our general approach to tracking down odors to their source here are some additional diagnostic suggestions:
Keep an odor log, noting when and where odors are worst (you already cite the kitchen area). Relating odors suspected to be due to plumbing vent frost-clogging to outdoor temperatures, wind, and fixture use could be diagnostic.
Note carefully where odors are worst: outdoors vs. inside (on occasion area wind patterns send plumbing vent gases down from a properly-working rooftop vent to lower building windows) and inside by room, fixture, and fixture use.
Often plumbing or sewer gas odors are ultimately traced to a loose toilet, a clogged drain, or an improper plumbing trap. But if we are sure that at your home the odor problem is new, and only a cold-weather problem, I suspect that the problem will be traced to something that has changed, such as a drain that is partly blocked, a vent that is partly blocked, a vent that has come disconnected somewhere in the building (it was never properly glued or soldered, or it was punctured or damaged) or similar damage to a building drain.
Keep me posted and we'll take it from your next report.
My husband just left Home Depot and got the heat tape, but will hold off after reading your response below. We have 2 toilets upstairs that keep running. One flushes on its own during the night and the other takes forever to complete a flush. Should my husband replace both toilets or should he just repair them? We need to address this soon because the weather just dipped again to 16 degrees and the smell which was gone for 2 days is back in full force again.
Here's where I'd start:
1. if you can't quickly fix a running toilet (you may need to replace a flapper valve or the fill valve) then turn off the water supply to the toilets that are running. IF there is no toilet shut-off valve, most likely you need a plumber to add one - at which case you'd also at the same time replace any parts needed to stop the running toilet problem in the first place.
2. If the drain is not totally blocked you can often remove the partial ice blockage it by running very hot water down the drain for a time.
Matt did a bunch of plumbing work on a bathtub & 2 toilets upstairs. He is off tomorrow from work and will be continuing his repair efforts. Once Matt has completed everything, I will let you know if the odor dissipates during cold weather. Thanks again Daniel for your awesome guidance and feedback.
I have no news to report yet. We have had 30 to 40 degree weather for several days, so the odor has not been present in the house. The weather is going to dip below 20 degrees again though. I can then see how things go with the cold weather odors. I am hoping all the plumbing repairs Matt did on the 2 toilets and bathtub upstairs make a beneficial difference. If not, Matt is going to wrap the pipe in the attic in electrical wire (heat tape). As soon as I have feedback, I promise to let you know. - M & S N 12/23/2013
9/11/15 Michael Mattingly said:
Lived in home 14 years (rural) with septic field. The septic ejector pump and storm drainage sump pump are located next to each other in downstairs bedroom. For years we have had sewage (intermittent trickle) coming from the storm drainage inlet line and dumping into the sump pump. Obviously, the smell is not good. We have had many plumbers come out. Septic field fine, septic tank fine, pipes no leaks, snaked storm drainage line--- when water is turned on from many in home sources--- they saw water coming in slowly.
They hit an elbow connection and couldn't see beyond that. I tried a dye test. Added dye to every toilet. Have noticed blue dye in storm drain sump pump. Assume coming from ejector pump leak? The ejector pump sewage collection is somehow communicating with the storm drainage system? Does this sound right? How can it occur? What do we do next? Thanks!!!
I am unclear on why you are citing sewage in the storm drainage sump pump. Can you clarify where the sewage effluent is appearing: the storm drain system or the sewage ejector pump?
If the former: the suggestion is that your septic system is in failure or sewer piping leaks and is e3ntering groundwater near the house.
If the latter the problem may be a flooded septic system during storms or a failed check valve at the ejector pump.
(Sept 10, 2014) Michael Mattingly said:
Lived in home 14 years (rural) with septic field. The septic ejector pump and storm drainage sump pump are located next to each other in downstairs bedroom. For years we have had sewage (intermittent trickle) coming from the storm drainage inlet line and dumping into the sump pump. Obviously, the smell is not good. We have had many plumbers come out. Septic field fine, septic tank fine, pipes no leaks, snaked storm drainage line--- when water is turned on from many in home sources--- they saw water coming in slowly. They hit an elbow connection and couldn't see beyond that. I tried a dye test. Added dye to every toilet.
Have noticed blue dye in storm drain sump pump. Assume coming from ejector pump leak? The ejector pump sewage collection is somehow communicating with the storm drainage system? Does this sound right? How can it occur? What do we do next? Thanks!
I am unclear on why you are citing sewage in the storm drainage sump pump. Can you clarify where the sewage effluent is appearing: the storm drain system or the sewage ejector pump?
If the former: the suggestion is that your septic system is in failure or sewer piping leaks and is entering groundwater near the house.
If the latter the problem may be a flooded septic system during storms or a failed check valve at the ejector pump.
If someone put a tracer dye into a building drain (like a toilet) and you are seeing that dyed water in the storm drain then it sounds as if the plumbing system is not connected properly and that it may violate your local building codes too.
(Sept 30, 2014) JBrooker said:
When we turn our kitchen or bathroom exhaust fans on for an extended period of time we get a septic odor. The odor seems to emanate from somewhere around our upstairs guest bathroom. When the kitchen fan is on, the smell comes out of one of the kitchen pot lights which is right below the bathroom (but is also mild in the bathroom). When either bathroom fan is on the smell is present in the guest bathroom. The odor does not appear to be coming from any of the drains in that bathroom (or any other drain) and the traps have all been kept wet. If anything, the smell also seemed a bit stronger under the sink where the pipe comes through the wall (which is directly above the pot light).
That being said, the smell was also noticeable when standing in that bathroom, which lead me to believe that it was coming from somewhere higher up than under the sink (but I couldn't pinpoint where)... The plumbing vent comes out of the house on the opposite side of this bathroom and is proper diameter. And there is no glub glub or gurgle sound from the drains ever. The pipe on the roof did not appear to be covered in snow or impeded in any way last winter when the smell was strongest. The house is very tight and does have a mechanical ventilation system in addition to the exhaust fans. It is not present at all when the exhaust fans are off. Is this odor caused by a leak in the pipe or back-drafting, or both? -- I also posted these comments in the article for back-drafting, but saw this one was more recent. Thanks
JB please see BACKDRAFTING & SEWER/SEPTIC ODORS
(Oct 11, 2014) LauraD. said:
3 years ago our home reeked of sewage. Upon peering in our crawl space under the house, we found it to be half full of raw sewage and had to call a company out who handles such things. Well every year since then, when the weather starts to change from warm to cold the stench of sewage reappears, but only in the bathroom. Lately it seems to be getting worse. My brother, who owns the house, and lives here, isn't concerned. Whereas, I have major health issues and cannot afford to stay in the house but also cannot afford to go elsewhere. If I hadn't been all over him about it 3 years ago, he would have lived in the stench until he got sick or something else happened.
Can you give me any ideas as to why this is happening, what we can do. I've read different things it could be and relayed this info to my brother and the plumber that he is NOT, tells me whatever I tell him is not the problem...and he hasn't even bothered to check anything out! I need some advice
Certainly you are describing an unhealthy and perhaps dangerous situation since both sewage hazards and possibly explosive sewer gas hazards could be present in the home.
(Nov 21, 2014) Marti said:
The article about the sewer gas in cold weather sounds like my situation. We have never had the pressure test or smoke test but I am thinking about it. We have all the other things done that you can think of.
I wanted to know if they ever found out where the problem was. We deal with this every winter and it really is starting to make me sick.
(Dec 23, 2014) Anonymous said:
Every winter when you start having to turn the heat on, we have a sewer smell. No particular area can be pin pointed. We have a basement, main floor, and upstairs. The sewer smell seems to be in the main floor of the house but with an open floor plan, it is in every area. I cannot find the cause and it is driving me mad. I cannot invite company over because of the odor. Why only in winter?
If you are talking about forced warm air heat - a furnace heating system - your air handler could be picking up sewer gas at an air return. Look there.
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