Quick Answer:
Cold weather can make drain smells seem stronger because vents, drafts and slower drainage change how sewer gases move and how well trap water seals. Start by confirming the sink empties normally (no standing water), note whether the smell is worse on windy days versus very cold still days, and run water longer than usual to fully refresh the trap. These simple checks will tell you whether it’s a ventilation issue, slow flow, or surface buildup.
Why This Happens
There are a few common winter mechanics that make odors more noticeable:
- Venting and drafts: Wind over roof vents or changes in air pressure can draw sewer gas past a trap if the trap water has been reduced.
- Slower drainage: Very cold pipes and slower flow from less frequent use let organic material sit longer, releasing more odor.
- Dry or partially empty traps: Less use of a fixture (common in winter) or evaporation can let the water seal drop and let gas through.
- Surface biofilm: Cold weather doesn’t eliminate the biofilm that produces smells; in some cases changes in use or detergents can make it more noticeable, similar to **Kitchen drain smells like garbage** or **Bio-buildup after switching detergent**.
Step-by-Step What to Do
1. Confirm normal drainage
Run the sink and watch it drain. There should be no standing water left in the basin. Standing water means a partial clog or slow drainage; that requires further clearing or professional help.
2. Test wind versus cold
Notice when the smell is strongest:
- If it’s worse on windy days, that suggests a venting or draft effect.
- If it’s worse on very cold, calm days, slow drainage or thicker waste may be holding more odor-producing material in the trap or pipe.
3. Refresh the trap water
Run cold and hot water together for 20–30 seconds, or run the tap for longer than you usually would, to fully exchange the trap water. Repeat at each fixture that smells. This replenishes the water seal and often eliminates lingering odors.
4. Clear partial clogs if needed
If water is slow, remove visible debris from the drain or use a plunger or a drain snake on accessible drains. Avoid aggressive chemical use; a focused mechanical clear is safer and often more effective in winter.
5. Keep fixtures used regularly
Flush rarely used fixtures (floor drains, guest sinks) weekly with water to maintain the trap seal. For very infrequently used fixtures, pour a cup of water down the drain occasionally to prevent drying.
What Not to Do
- Don’t cap or block any venting component to ‘stop drafts’—that can worsen trap siphoning and create bigger venting problems.
- If winter odors come with slow drains or gurgling, don’t ignore it — a plumber is appropriate for diagnosis and safe repair.
- Avoid pouring mixed chemicals into drains to “fix” the smell; mixing products can create dangerous fumes or damage pipes.
When to Call a Professional
- Persistent sewer-like odor after you’ve refreshed trap water and checked drainage.
- Slow drains, repeated clogs, or gurgling sounds from multiple fixtures.
- Smell that seems to come from multiple drains or from drains plus vents on the roof — possible venting or sewer line issue.
- Any time you suspect frozen vents or an inaccessible problem on the roof — leave roof work to a pro for safety.
Safety Notes
- Sewer gas in small amounts is usually just unpleasant; in enclosed spaces and high concentrations it can be hazardous. Open windows and ventilate when investigating strong odors.
- Don’t climb on a roof alone or try to alter roof vents yourself. Work at height is dangerous and best left to professionals.
- Avoid mixing chemical cleaners. If you use a commercial cleaner, follow label instructions and ventilate the area.
Common Homeowner Questions
- Why does the smell come back after I pour water down the drain?
If the source is slow-moving biofilm or a partially clogged pipe, water alone may only temporarily mask the smell. You may need to clear the pipe or have a plumber inspect the venting. - Will pouring bleach solve it?
Bleach can kill surface odors briefly but won’t fix venting problems or deep biofilm. Use it cautiously and don’t mix with other cleaners. - Can I cap the vent to stop the smell?
No. Capping vents can cause trap siphoning and worse sewer-gas problems. Call a plumber instead if you think venting is the issue.
For more related articles, see the Odors Originating from Bathroom Sink Drain hub.
For more related articles, see the Food Waste Odors & Bio-Buildup hub.