Bad odor is coming from the outside in

Question:

A pumper I know has a problem with septic odors appearing inside houses. Lots of houses in a small area. Some of the houses are old, some new. The problem seems to happen in the spring and fall, on a warm day following a cold night. He says it happens in his own house, and the odor is so strong that it smells like his service truck is parked in his living room. My thought is that it’s due to lower atmospheric pressure inside the house drawing odors into the house from outside. The problem goes away by noon every time. Any thoughts?

Answers:

If it’s a new home, check to make sure the vents are clear on the roof. Ask the homeowner if the sinks/toilet drain slow; if they do, the vents may be clogged.

Have the homeowner perform a manometer test. This will test the traps and verify it can hold pressure. If it is inside the home, this is the most likely culprit. They will have to cap the vents and the main line to the septic tank.

There are a host of other issues that can contribute to this as well. In one case, a homeowner’s vent was too short and when a building went up next to it, the wind swirled in a different manner and it took the vented gas right into the home. They extended the pipe and the problem was solved.

If there are lots of houses in a small area, it may be the neighbor.

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It is possible that the odors are originating from outside. It could be getting drawn into his heating system if the home has forced hot air heating. If the odor is originating from outside he should be able to smell it outside the home near where it is entering the house. Is the odor only in one room or on one level? Another possibility is either a restricted plumbing vent or a cracked vent pipe, but generally they will cause a problem year-round.

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I have seen this once before. We were able to determine that it was caused by unsupported horizontal vent piping in the attic, which created a trap and wouldn’t let the gasses out to the vertical vent. The problem was worse in the morning because the building was shut tight all night allowing the fumes to accumulate. After a while with doors opening and closing, the odor would dissipate. Once we supported the vent so that it could not trap water, the odor problems went away.

This reminded me of something else. Everyday I see rooftop combo units with the condensate drain running directly into the plumbing vent. This is fine in the summer time (not really fine, but causes minimal problems), but when the trap dries out in the winter, you are actually sucking sewer gas in through the condensate drain.

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Is there a dry P-trap in the home? An unused basement shower is a common culprit. Or is the washing machine discharge drained through an un-trapped connection, also a common problem?

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The odor mystery is usually found to be inside the trap in the basement, and sometime when the water drains out it leaves a muck in there that really reeks.

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Thanks for all the great input. The odor problem affects many houses, all on the same days. There is nothing in particular that the houses/families have in common. My customer believes the problem to be caused by atmospheric conditions and the weather. The only apparent commonality is the odors occur on warm days following cold nights in spring and fall. I’ve always thought odors are plumbing problems, which you all have mostly concurred with. Trap issues, etc. I’m passing all your ideas along.