Weird house smell

[jmc]

Hello,

Anyone care to guess what causes my intermittent sewer smell that is blown about the house thru the heat/cool ducts? It started about 2 years ago and it's sometimes there in both the heating and cooling modes. We have a septic system, an upstairs geothermal system, and a downstairs geothermal system. The smell is only from the upstairs unit.

John

 

[sandman2234]

That can be a load of questions to get a good answer for this one. Drain stopped up and causing the pan to overflow onto the ductworks, causing mold to generate and smell? Plumber ran the air vent up and thru the duct? Return air next to a seldom used bathroom and the kids aren't flushing it?
If you have any seldom used drains, especially near a return air, they might be dry, allowing backflow of air. We had that in a bathroom at a place I worked and we liked to have never figured it out. My smeller isn't that good and it was my job to fix it. Had several friends over to help, and we finally figured it out.
David from jax

 

[jinman]

Hello,

Anyone care to guess what causes my intermittent sewer smell that is blown about the house thru the heat/cool ducts? It started about 2 years ago and it's sometimes there in both the heating and cooling modes. We have a septic system, an upstairs geothermal system, and a downstairs geothermal system. The smell is only from the upstairs unit.

John

John, since you say, "...in both the heating and cooling modes," I am curious if this is a heat pump system? If so, you may be suffering from "dirty sock syndrome" that is common when the coils never get hot enough to kill bacteria. You may have to clean your system and/or install UV lights to kill bacteria and mold. With systems that use heating coils and other types of heat that goes above 130 degrees, the bacteria, mold, and mildew are not a problem. The "cool" heat of heat pumps does not get hot enough and smells are the first indication.

If you don't have a heat pump, I'd look at your air conditioning condensation drain. It probably goes right into the sewer and may not have a trap installed. It should have an S-shaped trap similar to any sink drain. If that trap is dried out or not there, sewer vapors are being pulled up into your system. If the trap is there an it is just dry, you may be able to cure the problem by pouring in a little water or dilute bleach. In the winter when you use only heat, there is no condensation and you may find it's easier just to plug it until spring when you return to air conditioning. Don't forget to take out the plug before turning on the A/C.

 

[gordon21]

Sandman has probably hit the answer for you. Toilet drains and P traps under other fixtures can dry out. Once that happens, sewer gas can pass through the P trap. All it takes to fix is to fill the trap. Since you say it is intermittant, that means you have NO problem part of the time. That rules out a bad vent system or broken vent pipe. That would cause a problem 100% of the time.

The gas once it makes it into the house will be sucked up and distributed by the HVAC system. In this case you are probably shooting the messenger by blaming the HVAC system. It is merely conveying the problem to you.

Gently pour 1 quart of water down every sink drain to make sure the P trap is full. Make sure all toilets have at least 4" of water in the bottom of the bowl. Fill the washer P trap and shower drains too.

 

[AlanB]

In the old house we bought, when I swappped out the air handler in the basement, there were lots of dead mice on the top of it. They would crawl down the vents, then go on top of the air handler (I bet for warmth) and could not get back up the coned inwardly sloping sides and die.

Talking to someone that had been in the house previous they mentioned how it had always been heavily scented with candles etc.

I bet they were covering the smell.

 

[NewToy]

I concur with the dry trap or broken vent diagnosis. While we were building our place we had the plumbing all done and would use the restroom as needed. The odor was coming from all the traps that were never/seldom used. It was easy to find the offensive trap, just like popping the lid off the septic.

John

 

[Champy]

I'll echo Jinman's comments about the condensation and S drain/trap.

I have this drain but it was plugged at the blower unit of my heat pump system. Stunk like stagnant swamp water and started flowing back into the air handling units. Cleaned out the trap and drains - everything is fine now with no smells. Some times of the year there was little condensation / humidity so no smell....other times whew!

 

[sandman2234]

AlanB,
Those mice were probably looking for water, rather than warmth.
David from jax

 

[jmc]

Hello,

Followup- After reading all your posts on Wednesday, I poured water in the basement floor drains and sump pump. The smell was gone later that day thru today.

That sump pump down there may be the culprit. We put it in when building the house in case we wanted to add a toilet later. it pumps into the pipe that runs to the septic and there's no trap between the pump and the crawlspace- the furthest I can trace the pipe. So if there's no trap in the crawlspace, or in the line from the crawlspace to the septic tank, should there be?

Thanks, everyone, for the help.

John

 

[jinman]

If you put water in the drain and the smell went away, it would seem that you replenished a trap somewhere in the line. Just rinsing out the line would not stop vapors from coming back up the pipe. However, if there is a hidden trap you are not aware of or a low place in the piping that is acting like a trap when full of water, then you may have found the problem. The fact that it's a sump says that water collects until you turn the pump on, and that may have sealed off the gas.