What Causes Sewer Smell in Your House
Sewer smells in your home are most commonly caused by dried-out P-traps in unused drains, a blocked roof vent, a broken toilet wax ring, or a cracked sewer pipe. Pouring water down rarely used drains is the easiest first step to fix it.
Dried Out P-Traps
The U-shaped pipe under every drain (the P-trap) holds a small amount of water to block gases. If a sink or shower goes unused for weeks, that water evaporates.
- Guest bathrooms and basement floor drains are the most common culprits.
- Run water in all sinks and showers for 30 seconds every few weeks.
- Pour a tablespoon of mineral oil into floor drains; it floats on the water and prevents evaporation.
Broken Toilet Wax Ring
The wax ring seals the base of your toilet to the sewer pipe in the floor. If it breaks or degrades, sewer gas will seep out from underneath the toilet.
- If the toilet rocks or wiggles when you sit on it, the seal is broken.
- Look for water pooling around the base of the toilet.
- The toilet must be removed and a new wax ring installed to fix the smell.
Blocked Vent Pipes
Plumbing vents run through your roof to let sewer gases escape outside. If they become blocked, the gases are forced back down into your home.
- Leaves, debris, snow, or even bird nests can block the vent opening.
- Listen for gurgling drains, which is a symptom of a blocked vent.
- Clearing the vent usually requires climbing on the roof or calling a professional.
Cracked Sewer Lines
If the smell is persistent and accompanied by slow drains or gurgling, you may have a cracked or broken main sewer pipe beneath your foundation or in the yard.
- Sewer gas contains methane and hydrogen sulfide, which are toxic and flammable.
- Never ignore a strong, persistent sewage smell.
- A plumber will need to perform a smoke test or camera inspection to locate the hidden break.
When to Call a Professional
Call a plumber immediately if the smell is strong and persistent, if drains are gurgling, or if pouring water in unused traps doesn't solve the problem.
What a Plumber Will Do
A plumber conducts a smoke test to visually locate hidden cracks or faulty seals emitting gas, and uses a camera to check the main line for breaks.
Frequently Asked Questions
Is sewer gas dangerous to breathe?
Yes. In high concentrations, hydrogen sulfide in sewer gas is highly toxic, and methane can be an explosion hazard. Prolonged exposure causes headaches and nausea.
Why does my hot water smell like rotten eggs?
If only the hot water smells, the issue is not a sewer leak. It is a chemical reaction between sulfur bacteria and the magnesium anode rod in your water heater.
What is a plumbing smoke test?
A plumber pumps harmless, non-toxic smoke into your drainage system. Wherever the smoke escapes into the house reveals exactly where the pipe or seal is broken.
Can weather affect sewer smells?
Yes, changes in barometric pressure or heavy winds can sometimes push sewer gas down the roof vents and into the home temporarily.