Why Does My House Smell Like Sewer Gas?

First, make sure it is sewer odor and not gas

Natural gas is odorized with an additive that many people describe as rotten eggs or sulfur, which overlaps with how sewer gas is often described. If you suspect natural gas, do not try to identify it yourself. Leave the building, avoid switches and open flames, and contact your gas utility or emergency services from a safe location.

Once gas is ruled out, the plumbing possibilities are straightforward to work through.

Check infrequently used drains

Every fixture has a trap that holds water, and that water seal is what keeps drainage odor out of the room. A guest bathroom, a basement or garage floor drain, a spare tub or a rarely used laundry standpipe can evaporate dry, leaving an open path.

Running water at each of those for a minute or two is the simplest test available. If the odor fades over the next day, a dry trap was likely the cause, and the fix is periodic use.

Notice whether plumbing symptoms accompany the smell

Slow drains, bubbling toilets or any recent backup shift the likely cause from a dry trap toward a drainage or venting condition. Odor that arrives at the same time as those symptoms should be treated as part of one problem, not two.

Look around fixture bases and connections

An odor concentrated around a toilet, especially with any rocking movement or discoloration at the floor line, may involve the fixture connection and seal. Under sinks, check that trap connections are snug and dry and that any appliance or condensate line entering the drain is properly connected.

Odor concentrated at one wall or ceiling area with no fixture nearby can point toward concealed drainage or vent piping, which needs to be inspected rather than guessed at.

Other odor sources that are not the sewer

Not every drain odor is sewer gas. Biofilm buildup inside a sink overflow, a garbage disposal that has not been cleaned, a shower drain with accumulated hair and residue, or a water heater condition can all produce unpleasant smells that are localized and improve with cleaning.

When to watch it and when to call

Watch it

The odor came from a clearly unused drain and faded after you ran water there.

Schedule an inspection

The odor persists after filling every trap, appears with no obvious fixture nearby, or comes with slow drains or gurgling.

Leave and call immediately

You suspect natural gas, or the odor is strong enough to cause headaches, nausea or dizziness.

Bottom Line

Start with location and usage. Filling dry traps resolves a good share of indoor sewer odors, and a smell that persists afterward usually involves a fixture connection, venting or a drainage condition. If the odor might be natural gas instead, leave the building and call from outside.

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