I smell what I identified as sewer gas in my home after it rains.  I’ve tried the smell test but I cannot locate the problem although it is stronger upstairs.  I’ve also noticed it is worse in the summer when it rains and my house is closed up because of air conditioning.  Now I have flu-like symptoms that have come and gone for several weeks.  Is there a possible connection?  If I call a plumber, what should I ask him to do?-  Sherree – Ft. Myers, FL 

            I would be surprised if the flu-like symptoms were associated with the sewer-gas smell.  However, it is possible if along with the sewer odor spores of sewage fungi were coming into your house.  I suspect that the odor is coming from vents in your sewage system.  The vents are supposed to carry sewer gases to a stack on your roof.  You should have one stack that serves your laundry-utility area and a second that serves one to two bathrooms. 

            One of those vents is likely to be leaking.  Though it may be water tight, it may not be airtight. 

            Sewer gas problems increase in intensity as pressure changes occur in the system and in your house.  If you are on a combined sewer system storm water flow causes sewer lines to fill up reducing the volume available for sewer gases.  These sewer gases to a degree become compressed; that is, they are under pressure.  As they become pressurized, they follow the path of least resistance.  This means they move toward buildings.  They will come up through dry traps and/or sewer vent systems. 

            When your air-conditioning system is operating, the house is closed up.  As such, you are more likely to smell sewer odors when they are present.  Closure conditions also change the pressure conditions in your house.  Houses tend to be strongly negative under closure conditions because of inside/outside temperature differences and the loss of supply air from leaky duct systems. 

            To locate the sewer gas source, use your “sniffer”.  It can detect some components of sewer gas (e.g. hydrogen sulfide) down to a few parts per billion.  In doing so you will have to periodically have your “sniffer” recharged.  Because of olfactory fatigue, our ability to detect odors decreases within minutes after exposure.  To recharge, go outside for a few minutes and then return.  You will notice the odor to being much stronger.  Repeat until you have pinpointed where the odor is coming from.

            Follow the sewer bathroom lines.  In your house they run vertically; under your house horizontally. 

           Since I wrote, I looked for the vent stack in my attic.  It was there but there was no pipe coming out of the roof!  The vent pipe simply ends at the top of my attic and is open.  The smell is very obvious when I get close to it.  My air handler is in the same space as the vent pipe and my bedroom is next to the door that leads into the attic.  I have called a plumber who will either vent the stack to the roof or put a cap on it that allows air in but does not allow fumes out.-Sherree