Searching for basement smell source

[MerlinsBeard]

I have a smell in the basement that has appeared recently and I'm trying to determine the source. The basement is unfinished with a sump pump and stubs for future bathroom in the slab. The house is about 13 years old and as far as I can tell I do not see any standing water anywhere on the floor or wetness on the walls. I put a hygrometer down in the basement and it's been about 45% humidity for about a week.

There was one interesting situation that happened before the smell started. For about a two or three day period, the air from the air conditioner was noticeably colder than normal. When I went into the basement, I noticed that there was condensation on the outside of the ductwork in the basement near the furnace, maybe 15 feet or so. There were no droplets, but there was definitely condensation where if I wiped my finger it would leave a streak. We turned up the thermostat temperature to compensate and the moisture appears to have abated at least on the ductwork surface. Unfortunately I did not have a hygrometer when I noticed this issue.

I suspect that we may have mold or mildew but don't know how to confirm it. I don't think it smells like sewer gas, and there's no obvious damage around the bathroom PVC stubs. It doesn't smell stronger near the PVC stubs or the sump pump that I can tell. You walk down into the basement and you can notice the smell. I can try to look around with a mirror in the ductwork or perhaps open a panel on the exchanger, though I don't have any experience in this area.

The smell is not constant, and is pretty isolated to the basement so far. If I need help, who is the right service to call? Call the HVAC, or someone more specialized? I can start with the HVAC and go from there since we did have a build up of moisture in the basement.

I have had a natural gas leak in the basement before and it does not smell like that.

Anyone with similar experience?

 

[jkuro]

I would start by putting In a dehumidifier.

GE 50-Pint Dehumidifier with Built-in Pump for Basement, Garage or Wet Rooms up to 4500 sq. ft. in Grey, ENERGY STAR APHL50LB - The Home Depot

www.homedepot.com

 

[Solpainter]

If you have floor drains hooked to a sewer system be sure they have water in them as you may be having sewer gas coming in.

 

[larry4406]

Sweating duct work and perhaps colder than normal air for a period of time tells me that your AC coil likely froze over. This happens when filters are not replaced periodically and air flow across the coil is reduced. It can also happen when the freon charge is improper.

Check your filters.

Ensure the basement has a cold air return. Many unfinished basements don't which I think is wrong and contributes to musty smells in the basement. Ensure the basement has supply ducts so it is tempered and has turnover of air via the basement return. Ensure the plumbing drain rough-ins are properly sealed.

Agree with running a dehumidifier plumbed to a floor drain in the basement. I have mine set to continuous run. I added a cold air return at my unfinished basement.

 

[Paco Pena]

Check for dead critters as well.

Paco

 

[NUTTSGT]

Like above, that's where I would start.

Floor drain and any other drain, make sure they have water in the P-trap.

Check your furnace filter, especially if you have pets...we probably have 10-12 calls a year due to furnace filter issues.

Dead mouse ?

What does it actually smell like or similar to ?

 

[zendriver]

Sewer gas?

We had some coming up through where the washing machine drain entered the system.

 

[545_days]

A dead mouse will do that too.

 

[Wrench97]

Where does the condensate line from the A/C unit drain?
If the issue was inside the duct work you would be blowing the odor throughout the house through the vents.

 

[oldmachinenut]

Jimmy Hoffa under the slab?

 

[PCustoms]

Propane leak?

https://www.garagejournal.com/forum/threads/just-reflecting-on-the-fragility-of-life.537664/

 

[RegeSullivan]

Was the AC actually "noticeably colder" or was that assumed because of the condensation on your duct work? If you don't really know the AC was colder than normal you might want to look for reasons the humidity was higher than normal when you found the condensation. Maybe an intermittent plumbing problem or a foundation drain not working as well as it used to. Concrete will wick water up and evaporate quickly without showing and sign of water on the surface.

What ever the source I hope you find it quickly.

 

[MerlinsBeard]

Thanks for the ideas... unfortunately I've not had a repeat of the smell in the basement for about five days. I will try to investigate and report back as I notice anything.

 

[MovingAlong]

Thanks for the ideas... unfortunately I've not had a repeat of the smell in the basement for about five days. I will try to investigate and report back as I notice anything.

If the smell only occurs on a cycle or periodically, start taking notes on what other systems are operating on a similar pattern.

Was it a hot day, a cold day, a rainy day? Lot's of people using the house? Nobody using the house? etc...

 

[MerlinsBeard]

When I was running into the smell, the smell seemed the most pronounced in the morning when the outside air was very humid in the morning (fog on the windows and cars) and the day was on the warmer side (temps 80F and up). It hasn't been that humid lately, so I suspect that the smell will be back eventually.

The smell lasted off and on for about 10 days in total, where you'd have 2-3 days and a break, then it would repeat with less strength. So far this is day 6 with no basement smell.

I've been monitoring with a hygrometer and the humidity has been in the 45-50% range every day that I've been tracking it.

The smell came when we were using the house, so no long vacations when the smell appeared.

 

[akellum]

You mentioned that you didn’t think it was sewer, but I had a similar situation in our house. Unfinished basement, roughed in for a bathroom, with sewage ejector for the basement plumbing. I would occasionally get a slight sewer odor every few months.

My issue was that the ejector pit was installed, but not the pump. The basement bathroom plumbing vents were connected as part of the rough-in. It took a while to figure out, but in some wind conditions sewer gas was being pushed down the vent, to the (dry) underslab drains and into the unsealed ejector pit. Finishing the pump install and sealing the pit stopped the odors. It might be worth making sure the plumbing is well sealed.

 

[jkuro]

If the water in the trap is evaporating, fill the trap back up with water, then put a small layer of cooking oil on top. This should keep the water from evaporating and sewer gas from getting in.

 

[dogdog]

Maybe hire a plumber with a pro snake cam? If you are saying that smells only when you are using the house. Could be you busted a drain line some where.

 

[nadogail]

Trap Primers often help with unexplained odors.

 

[gahrajmahal]

For floor drains, RV antifreeze ( used in their plumbing systems) will not evaporate and it smells good too.

 

[MerlinsBeard]

You mentioned that you didn’t think it was sewer, but I had a similar situation in our house. Unfinished basement, roughed in for a bathroom, with sewage ejector for the basement plumbing. I would occasionally get a slight sewer odor every few months.

My issue was that the ejector pit was installed, but not the pump. The basement bathroom plumbing vents were connected as part of the rough-in. It took a while to figure out, but in some wind conditions sewer gas was being pushed down the vent, to the (dry) underslab drains and into the unsealed ejector pit. Finishing the pump install and sealing the pit stopped the odors. It might be worth making sure the plumbing is well sealed.

I think this is currently the likeliest culprit. It's hard to pin down, but when the smell is lighter (doesn't permeate the whole basement), the vague smell does seem to be stronger from the sump pump area, which has the pump but the ejector pit is unsealed.

 

[uratool]

Had an intermittent smell in the basement I couldn't locate, bought a cheap ($30?) natural gas detector off amazon, immediately found the source was the crock seal for the ejector pump out to the septic. Turns out if the wind was from the right direction the gas would leak into the house.

The real issue was a partially clogged air intake for the heat recovery ventilation system that was creating negative pressure in the house...cleaned the intake screen and rebalanced the system and the smell was gone.

The gas detectors are so cheap now that it might be worth a shot?

 

[Fav Onefour]

I think this is currently the likeliest culprit. It's hard to pin down, but when the smell is lighter (doesn't permeate the whole basement), the vague smell does seem to be stronger from the sump pump area, which has the pump but the ejector pit is unsealed.

What do you mean by ejector pit unsealed?

BTW, did you put in a dehumidifier? It seems hard to believe the humidity is 45-50% and causing condensation on ductwork with good flow. That would lead me to question if the humidity is really that low or if there are airflow issues in the HVAC system. Did you have the windows open at night during the period of high humidity?

High humidity can cause a stink that builds up over time. It would be nice to verify that is not happening. I have quite a few hydrometers scattered through various buildings. Basement areas run higher humidity unless they are managed. It usually takes quite a bit of time to dry out a humid structure. You might dry down the air fairly quickly, but the building materials hold onto the moisture much longer.

 

[MOS3522]

We need more info on the smell. Sewage? Dead animal? Musty/moldy? Taco Bell aftermath?

 

[mjweimer]

Out of lurk mode...

If the ejector pit is unsealed because there is no pump but there are drains roughed in...do you also have an open plumbing vent roughed in to the area of the pit? If so, you could be getting a whiff of the venting system from the other active drain/vents tied in to the system during certain weather conditions or when there is negative pressure in the basement.

 

[mreisner]

For floor drains, RV antifreeze ( used in their plumbing systems) will not evaporate and it smells good too.

RV antifreeze can and does evaporate, it is just alcohol and water. It doesn't evaporate as fast as water but it does still. I found that out the hard way in a camper toilet.