How Summer A/C Use Can Lead to Sewer Gas Odors

...And What Your P-Trap Has to Do With It

If you’ve ever walked into your basement or bathroom during a hot summer day and thought, “What is that smell?” you’re not alone. Sewer gas odors in the summer are a surprisingly common issue, and while they may not be the first thing that comes to mind when you think of warm-weather plumbing problems, they can quickly become unpleasant.

In many cases, your air conditioner is the hidden culprit. Running your A/C nonstop can dry out your plumbing traps --or, "P-traps" --allowing sewer gas to creep into your home.

What’s a P-Trap, Anyway?

A P-trap is the curved pipe you’ll find under sinks, tubs, showers, and floor drains. Its job is simple: It holds a small amount of water that acts as a protective seal, blocking smelly sewer gases from coming up through the drain and into your home.

But in the summer, especially when your A/C is running a lot, that water can dry up faster, especially in drains you don’t use often. Once the water is gone, nothing is stopping those odors from sneaking in.

More Than Just a Bad Smell: How Dry Drains Can Let Harmful Sewer Gas Into Your Home

Your A/C doesn’t directly affect your plumbing, but it can dry out the air inside your home. When indoor air is dry, water in unused drains can evaporate more quickly than usual.

This is most common in places like:

• Basement floor drains
• Guest bathrooms
• Unused tubs or showers
• Laundry sinks

Once the water in the P-trap evaporates, the protective seal is broken, and sewer gases can rise up through the pipes and enter your living space. Sewer gases can smell really bad and may be harmful if they build up in your home. Breathing them in for too long can cause headaches, dizziness, irritation in your eyes and throat. In closed-off areas, the gases can also lower oxygen levels or even become a fire hazard.

To prevent this:

• Run water through unused drains (sinks, tubs, floor drains) every couple of weeks.
• Let the water run for 10–15 seconds to refill the P-trap and block odors.
• For floor drains, pour a small amount of mineral oil after the water to slow down evaporation and keep the trap sealed longer.

When to Call in The Pros

If sewer gas smells persist even after refilling the traps, there could be a bigger issue at play, such as:

• A cracked or broken trap or pipe
• Improperly vented plumbing
• A clog or sewer line backup

If you notice sewer gas odors or suspect dry drains in your home, don’t wait for it to get worse. Contact Atlas Butler for a full plumbing inspection, or ask about how our team can help maintain your HVAC and plumbing systems together for year-round comfort and safety.

Call us anytime at 1-800-FURNACE or visit atlasbutler.com to schedule your plumbing inspection.