Why Is There a Sewer Smell Coming From My Drains When It Gets Cold Outside?

People living in Fort Worth and Arlington homes may occasionally get a whiff of something unpleasant during strong cold fronts. The smell usually appears suddenly, lingers for a few hours or a day, then disappears just as quickly.

Cold weather does not create sewer gases, but it can bring the right mix of atmospheric conditions to reveal issues in plumbing vent systems or P-traps that normally stay hidden.

How P-Traps Work and Why They Are the First Place Odors Escape

Every sink, tub, shower and floor drain has a P-trap, a curved section of pipe that holds a small amount of water. This water forms a seal that blocks sewer gases from entering the home. If the trap dries out, is siphoned or is unusually shallow, odors can move directly into the room.

P-traps can dry out if a drain goes for months without being used, which sometimes happens in unused guest bathrooms or similarly out-of-the-way fixtures. Indoor air also tends to be drier in December and January, which speeds evaporation in unused traps.

Once the water level in the trap drops low enough, sewer odors can pass through the drain during pressure changes.

Why Cold Fronts Create Pressure Changes That Pull Odor Into the Home

When a strong North Texas cold front arrives, the barometric pressure drops quickly. This shift affects the airflow inside your plumbing system. Lower pressure inside drain lines makes any weak or partially dry trap more prone to allowing odor through. Homes that have bathroom exhaust fans, dryers or fireplaces running may also develop slight negative pressure indoors. That pressure difference can draw air up through vulnerable drains, creating a noticeable odor even though the sewer system itself is functioning normally.

Wind Direction Shifts Can Push Odors Back Toward the Roofline

Your home’s plumbing vent stack releases sewer gases safely above the roof. During certain wind conditions, especially when a cold front pushes strong gusts across the roof, the air around that vent can be pushed downward.

If the attic has air leaks or if there are gaps around the vent penetration, the odor can be pulled into the home and appear near a bathroom or hallway. Homeowners often assume a drain is the source even though the smell is actually coming from the roof vent.

This effect usually clears once wind direction stabilizes or the front has passed.

Temperature Drops Increase the Chance of Trap Loss and Odor Migration

Cold fronts also change how air moves inside your home. Warm indoor air rises and escapes through attic or wall gaps, creating a slight upward pull known as stack effect. If a nearby P-trap has partially evaporated, that upward pull can draw sewer gases inside. Heating systems running more often during cold weather can reduce indoor humidity, causing unused traps to dry out even faster.

The first thing you should do if you notice a sewer smell in a bathroom or near a drain is to run water in it. In many cases, the odor disappears quickly after the trap is refilled.

When the Problem Is a Venting Issue and Not a Cold-Front Side Effect

Cold weather can expose underlying vent problems that really should be corrected by a licensed plumber. Vent-related odor issues often include:

• A roof vent partially blocked by leaves, debris or nests
• A vent pipe broken or separated in the attic
• A drain that frequently gurgles or loses its trap seal
• A fixture that smells year-round, not just during cold fronts
• Plumbing modifications that were not vented correctly

These problems allow sewer gases to move through the system more easily, and cold fronts simply make the symptoms more noticeable.

Rare but Possible: Frost Caps on Older Metal Vents

In freezing, humid conditions, frost can form on older metal vent stacks and temporarily restrict airflow. This is uncommon in the Fort Worth area, but it can occur during prolonged cold spells. If the vent is partially blocked, pressure imbalances in the drain system may allow odor to travel through traps or through gaps in the attic.

When Unexplained Foul Odors Justify the Attention of a Plumber in Arlington

If you’ve run water down a drain but the smell doesn’t go away, or if the smell recurs after every cold front, lingers in a specific room or comes with gurgling sounds or slow drainage, you should call a plumber to inspect the vent stack and drain system.

Tom’s Mechanical can quickly evaluate your issues and help restore normal operation to keep sewer odors out of your home. Call us at 817-277-4493 to request service.