Drains & sewer
Why Does My Basement Floor Drain Smell?
Updated · Kestrel editorial · 2 min read
Why traps dry out
Floor drains in Colorado basements are rarely used, and dry winter air evaporates the water seal. Once the trap is dry, sewer gas can rise through it.
Simple fix
Pour a gallon of water into the drain, then a small amount of mineral oil to slow evaporation. Some homeowners install a trap primer or a one-way drain insert.
When it's more than a dry trap
Look for:
- A missing or loose cleanout cap near the drain
- Water backing up into the drain after laundry or showers
- Gurgling sounds from the drain
- Wet or stained floor around the drain
When to call
Call if the smell persists after refilling the trap or the drain backs up, since that points to a blockage or a broken line.
Northern Colorado specifics
Dry winter air and forced-air heat evaporate trap water faster than in humid climates, so floor drains in finished basements in Fort Collins, Loveland and Greeley often dry out within a few weeks. Many newer homes have a trap primer that refills the trap automatically; if yours has one and the smell persists, the primer may have failed.
Other sources of basement sewer smell
If the drain isn't the source, check:
- A sump pit without a sealed lid
- An unused basement shower or laundry sink with a dry trap
- A loose toilet wax ring in a basement bathroom
- An ejector pit lid that isn't sealed
Call a professional if
- Water draining slowly
- Standing water in the tub
- Gurgling sounds
- Bad smell from the drain
Why Does My Basement Floor Drain Smell?: follow-up questions
Is sewer gas dangerous?
In small amounts it's mainly unpleasant, but persistent odors should be fixed.
How often should I add water to a floor drain?
Every few weeks in dry months.
Can a floor drain back up?
Yes, if the main line is blocked; it's often the first place water appears.
Can I pour bleach down the drain to stop the smell?
Bleach may briefly mask odor but won't fix a dry trap or a broken line, and it shouldn't be mixed with other cleaners. Plain water refills the trap, which is what stops sewer gas.
Should the drain be capped permanently?
Floor drains are there to handle water heater, washer and plumbing leaks, so they shouldn't be sealed shut. A one-way insert lets water in while blocking gas.
Every home differs; editorial standards.