Sewer gas smell in my home: I seriously need a good plumber to take a few minutes and read this and help me fix this problem.

I am pretty good at web searching and I have read every possible article I could find, including answers to simliar questions by other homeowners - and I still can't correct the problem.

The house is a log cabin (professionally built in 1999 from 100+ year old hand hewn logs from a torn down tobacco barn). There is a full crawlspace (4.5' high) where the furnace (high efficiency propane) and hot water heater are installed. The plumbing is easy to get to and inspect from the crawlspace.

Of course I have already eliminated the most basis causes of sewer smell. All of my drains have proper traps and none of the traps are dry. I do not have gurgling in any drains and no bubbles coming up in the toilet. The ring below the toilets are sealed properly. I can stick my nose to any drain and do not smell anything. The crawlspace is dry and clean and does not smell.

The smell becomes apparent when the furnace starts running - not always, sometimes a couple of days will go by and sometimes it will happen a couple of times every day. I have sat working at my desk for hours with the furnace kicking on and off and no smell - then all of a sudden the furnace kicks on and here comes the smell - not a light smell, but an obnoxious one. It doesn't appear to have any regular pattern or anything in particular that "sets it off" (like after running water or flushing a toilet, etc).

Because the smell seems to only happen when the furnace runs I was sure that sewer gas was somehow entering the furnace intake. I inspected the furnace and plumbing and there was only two places that the furnace connects to the septic system (the furnace condenstate drain line and the furnace in-line humidifier drain line). I have temporarily re-routed both these lines to my sump pump which bypasses the septic system and drains outside to a field. That didn't help. There are no leaks in the furnace intake ducting under the house (I inspected and re-taped all duct joints with foil tape to be sure).

So, my crawlspace does not smell, my intake ducts are sealed and taped properly and as indicated, I have removed the only direct links from the furnace to the septic system - yet I still have sewer gas entering the house through the heating vents??

I will mention that the furnace has a PVC pipe that comes out of the furnace fuel re-burner and is piped just outside the house. Whenever the sewer smell is coming in the house you can go outside and smell it clearly coming from the furnace exhaust also. I spoke to the furnace guy and he said there should not be a smell coming from that pipe - only forced air and some amount of condensate.

I went onto the roof to inspect the plumbing vents for blockage (even though I am led to believe that I should hear gurgling if the system is gasping for air) and there ARE NO VENTS on the roof (and none running up the side of the cabin). I went into the crawlspace looking for the vent lines and I found two vent lines total, one at each of the toilet drain lines. There are no traps in the toilet drain lines - they just pipe straight to the main septic line (I assume the water in the toilet bowl serves as a trap). The vent lines are attached to a fitting just above where the toilet lines connect.

I traced the vent lines into the house and to my surprise both lines enter the main floor inside the bathroom walls. The lines do not come out of the ceiling above the walls and they do not elbow out of the side of the house either. I will mention that these are not drywalled and painted walls - they are interior non-insulated walls with wood planks with enough spacing between the boards that they are by no means anywhere near air tight.

I have already looked at the possibility that I am mistaking a propane leak for a sewer smell. I have had two contractors test for propane leaks - and, with the design of the furnace which re-burns the exhaust before it leaves the house, I can't see how the smell coming from the exhaust line could possibly be propane.

I understand that log homes are unique and maybe you have to do things different because it is not feasible to drill a hole through the logs - and with the cathderal ceilings and no true attic, there is no place to route the vent lines to the roof > but is it correct to stub them off inside of a first floor wall?

I am stumped and need help.





































































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Very detailed post of problem and must be frustrating. There are number of things that can cause this and I assume you made sure all trap have water in them and toilet wax seals are good. The best way to solve this now is to smoke your house! Some plumbers have a machine that blows smoke into your entire house drainage system after capping off the vent and line heading to septic tank. You won't need to run the furnace to find the problem, just look for the smoke.

Edit: Check your local tool rental, you can rent the smoke machine also.

"There are no traps in the toilet drain lines " don't worry about this, the trap in built into the toilet. I have a log home too and its always hard to tell what they heck they were doing in different stages of construction. It sounds to me that the rough in plumber did something a bit too creative and useda whole house AAV (air admittance vent) or just vented into the wall cavity. You have no vent exiting the roof so he did one of the two and it doesn't amtter which, you must start opening walls until you can fin where those internal vents terminate. Once you find the end of the line come back and tell us what you found. Before you open the first wall gooutside and inspect the exterior wall surfaces just below the eaves to see if the plumber didn't vent through the side wall.

The toilet plumbing vents must be on the exterior of the home. Lets hope no one left a vent open inside the wall rather than running the vent all the way to the exterior. When the furnace kicks on it is creating a draft and letting odor come in from either the open pipe in the wall, or a leak in the sewer vent. Good luck with this, I have a 1920's house and have had similar issues with rigged plumbing.

JWH did a good job describing what happens in a log home. Once the logs are set and the shell closed in with interior walls and headers in place then the electrciian and HVAC are called. They have to get real inventive some times. Mine was vented through the wall just under the eaves, so I installed a 90 and went into the eave and up through the roof via a boot jack and flashing. My builder was over inventive.

TO: ballengerb1

I did as you said and looked outside under the eaves and found no vents. I then opened one of the interior walls and YES, I found that the plumber has terminated the vent lines inside the interior walls. There is a vented fitting attached to the top of the vent line. This same situation apparently exists in the interior wall of the other bathroom since there is no evidence of it exiting the home.

From everything I described in my initial post do you believe that the vent lines terminating inside the walls is the cause of my problem? If so, what do you suggest?

Continuing the vent up through the roof is not an option because of the log home design (directly above the vents would be the center of the floor in the two lofts and there is no confined space to run an elbow to run it through the side of the house).

In your reply, please advise if I could possibly cut these vent lines under the crawlspace, attach an elbow, run it through the wall (they would exit about 18" above ground level), then add another elbow and run the line up the side of the house? In this regards - is there any particular height that a vent line must run? Does it have to extend to the roof, or is just getting the line outside of the house all I need?

I very much appreciate your help.

I think you found the problem of the sewer gas source. That fitting you mentioned on the end of the vent pipe is likely a AAV that isn't working properly. The air admittance valve should only let air to enter (admit) and not let sewer gas out. It may be stuck open and I don't recommend repairing them, just replace it. The AAV worked for years and a new one should solve your issue. Do not cut in the crawl and try to vent there , its too far downstream in your plumbing system.

I am experiencing the same issue in my home. The issue only seems to be in the colder months when we heat the house. So my question is why would it only happen when the furnace is running in the colder months and not when we use the central A/C in the summer? Both use the same ducts, same return. My duct work is in a crawlspace as well (although not sealed with mastic and tape but I plan to do so), but the crawlspace is dry, odor free and all walls and floor are covered with 6 mil plastic. All plumbing is in the crawlspace as well. There are two vents on the roof but one is for our radon mitigation system so I assume the other is for plumbing and if I remember correctly the odor problem existed before the radon system was installed. We only have one bathroom and no traps can be dry because the bathroom sink, kitchen sink, shower and toilet are all used daily and even the washing machine is used multiple times a week. We are connected to city sewer and water and not on a septic.

Just out of curiosity, JWH188, did replacing the valve that ballengerb1 mentioned solve your issue?

Maybe I should have also mentioned that water heater and furnace are electric; only gas appliance is stove. The water heater and furnace are both on the main level and in a small mechanical room which also has the opening to the crawlspace and attic area. The odor seems to be the strongest in this room when you can smell it throughout the whole house.

You got tons of good advices from our Experts above... but I still don't see the correlation between smell and running furnace. Where is your central heater intake ? Is it forced air unit ? If the intake is inside your house, open the register and look inside. Look for dead animals, fungus, mold etc. I would suggest that you repaint it...

If the AAV vent is malfunctioning, there should be smell 24/7. That PVC pipe terminated on the outside: does it have a screen or some kind of cover on it ?

Sewer gas can be mistaken for other chemical odor when exposed to higher-than-room-temperature heat - like various wood treatments, lacquers, stains, varnishes, etc. Or could it be that you have dead animal, or perhaps fungus, inside the furnace itself or the distribution ducts ?

Question: do you live in the cabin full time ?

Couple of years back we have installed free standing shower on slab. Customer complained about sewer gas inside the shower. He claimed that every time he takes shower - he can smell this sewer-like odor apparently coming from the drain. He questioned presence of P-trap. No matter what we told him - he insisted that we dismantle the shower and show him the trap which "certainly" is the cause of smell. We did so. Trap was there. The problem turned out to be the smell of the new materials the shower components were constructed of. When the hot water hit the floor and walls, it smelled like sewer inside. The shower was made in China and they used recycled plastic for pan and walls. It took about 6 months for the smell to go away.