How to Know If You Smell Sewer Gas—or Something Worse

You and your family just returned home from vacation. You're tired, but happy to be home. As you turn the doorknob and go inside, you smell an unpleasant, sulfuric odour. Is it your sewer drain, or some other problem? You feel unsure.


A gassy smell isn't something you should ignore, but until you have better information, you may make a critical judgment error. Educate yourself first so you will know what to do after smelling gas.


Natural and Propane Gas
To rule out a dangerous gas leak, you need to understand how gas works. On its own, natural gas has no odour. However, your gas provider accounts for this by adding an extra chemical: mercaptan. If the air smells slightly musky or skunky, that's the mercaptan, a mild sulfur compound.


Since natural gas is lightweight, it rises in the air. By contrast, propane gas (the type you'd use for your patio barbeque) is heavy, so it sinks. When you understand the properties of gas, you'll be able to predict its behaviour more easily.


Sometimes you won't know the source of the smell. The gas odour may be strong in the hallway or next to one of your closets. It's tricky to find the source when you smell gas in general areas that are farther from pipes.


If you have an empty spray bottle, fill it with a soapy solution (two-thirds water to one third mild dish soap). Spray the soap lightly on visible pipes.


If the pipe is leaking gas, it will create air bubbles in the soapy solution.


Find the Gas Shut-offs

If you fear a natural or propane gas leak in/near your home, you'll be a step ahead if you can shut off the main gas valve. First, leave the house. Next, locate your gas meter; it's usually easy to spot either at the front of your home or near the side.


The gas shut-off is generally below the meter box itself. Look for a service pipe exiting the meter and running into the ground. The valve should be on that pipe. Before you do anything, call your gas provider. If instructed to do so, you can use a pipe wrench to shut it off.


Warning: this should only be done in an emergency. Otherwise, wait for authorized service personnel to arrive.


Sewer Gas
Like natural gas, sewer gas has a sulfuric odour. However, sewer gas generally smells more like rotten eggs and less like a skunk.


The problem comes from a backup of sulfides, ammonia, methane, and other inorganic compounds. In low doses (and in most homes), sewer gas is harmless enough—even though it's unpleasant. It's only dangerous in high doses (i.e., in a deep sewage tunnel).


Ask Your Plumber
Although they're relatively safe, sewer smells are never pleasant. Call our plumbers at EZ Plumbing to report the problem; then, mention where you smell the strongest odours. Chances are that our plumber will know the cause even without seeing it in person.


Our plumber can help you rule out a natural gas leak by asking a few questions. If it's really a sewer problem, it won't be hard to fix. Once your plumber arrives, he or she will get right down to business.


Likely Suspects
Most sewer problems originate in a couple of locations:

  • P-traps – These u-shaped pipes connect under the sinks in your home. If they dry out in the lowest, middle section, sewer smells are no longer "trapped" in water. That makes them obvious to everyone indoors.
  • Unconnected pipes – Do you have an interrupted plumbing remodel somewhere in your home? If so, you may have a disconnected pipe somewhere. Double-check.
  • Damaged line – If your drain line is broken somewhere between the sewer and the P-trap, gas can seep out along the path. Your plumber can inspect pipes and find the damage.
  • Damaged vent – Your plumbing vents equalize pressures in your plumbing system. When they're plugged or broken, sewer gas can escape.
  • Cracked seal – Your plumber can check to see if wax seals are cracked or crumbling. If so, they're a standard replacement.
  • Foundation cracks – In some cases, sewer gas can get inside your home even if nothing's wrong with the internal pipes. Have your plumber check your foundation if the sewer smell doesn't go away through other fixes.


Remember, although it takes a large concentration of sewer gas to cause health or structural problems, that doesn't mean you can afford to ignore the problem (not that you will want to; the odour is plenty of motivation to call your plumber).


While you're at it, schedule a plumbing inspection every year so you always know the state of your pipes and sewer drains. Meanwhile, unless you have experience with sewer problems, don't try to fix the problem yourself.


Sewer smells don't have to wreck your day. Open the windows (if the season permits), call us at EZ Plumbing, and let us take care of the rest.

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