Odor only at night

Quick Answer:

If you only notice a sewer-like smell when you come inside at night, it’s often caused by dry or partial traps, pressure changes from HVAC or fans, or a venting issue. Start by noting when the smell appears and top up nearby traps before bed. If the odor keeps returning each night or you see signs of a blocked vent, call a professional.

Why This Happens

Common reasons for a smell that shows up only at night include:

Traps that have lost water during the day and allow sewer gas through when the house is still or less ventilated.
Negative pressure from running exhaust fans, furnaces, or other HVAC equipment that pulls air from drains if traps are weak.
Intermittent vent blockage—an animal or debris partially blocking the roof vent can allow gas to build up and escape in odd ways.
Changes in household activity: reduced window opening and lower ventilation at night can make faint odors noticeable.

If the issue seems intermittent, also consider reading about Smell comes and goes to compare symptoms and timing.

Step-by-Step What to Do

1. Note times and HVAC activity

Keep a simple log for a few nights: what time you re-enter the house, whether the furnace or AC is running, and whether any exhaust fans were on. Patterns (same time each night or tied to HVAC cycles) point toward pressure or ventilation causes.

2. Top up nearby traps before bed

Run water in the sink, bathroom tub, and any floor drains near where you smell it for 20–30 seconds before you go to bed. This restores the water seal in traps so sewer gas can’t pass through.

3. Check exhaust fans and the furnace for negative pressure

Turn off bathroom fans and any high-powered exhausts, then enter the area to see if the smell changes. If the odor appears when these are running, they may be creating negative pressure that pulls air from drains. A brief test can help identify which appliance is involved.

4. Open a window briefly as a pressure test

At night, open a window near the affected room for a few minutes. If the odor dissipates quickly, that suggests a pressure-related backdraft rather than a continuous source inside pipes. Close the window and note whether the smell returns.

5. Inspect the roof vent from the ground

Do a visual check of the vent(s) on your roof from the yard or with binoculars. Look for obvious obstructions like leaves, a bird nest, or visible damage. Do not climb onto the roof yourself; if you cannot clearly see the vent, have a pro inspect it safely.

What Not to Do

Do not assume it’s harmless just because it happens at night. Recurrent sewer odors can indicate a real plumbing or venting problem.
Do not mask the smell with air fresheners, incense, or scented candles. These hide clues and make diagnosing the source harder.
Do not climb onto the roof yourself to clear vents unless you are trained and equipped to work safely at height.
Do not delay calling for help when odors recur nightly despite topping up traps or if you suspect the vent is blocked.

If the situation followed a municipal shutdown or pipe repair, review experiences like those described in Smell after city outage for additional troubleshooting steps.

When to Call a Professional

If the odor returns every night after you’ve topped up traps and checked fans or windows.
If you see signs of a blocked roof vent and cannot safely inspect or clear it yourself.
If the smell is strong, makes household members feel sick, or you detect other signs of a sewer leak (wet spots, slow drains, or gurgling noises).

A licensed plumber can perform a smoke test or camera inspection of vents and stacks to find blockages or leaks safely.

Safety Notes

Sewer gas can contain harmful components; persistent or strong odors deserve prompt attention.
Avoid DIY roof work if you’re not trained—fall risk is real. Use binoculars or hire a pro for roof checks.
When testing with windows or fans, do so briefly and cautiously; sudden drafts can stir up debris or allergens.
If anyone in the home experiences headaches, dizziness, nausea, or other symptoms when the smell appears, leave the area and call for professional help.

Common Homeowner Questions

Could this be sewer gas?
Yes—especially if the odor is musty or like rotten eggs; start with topping up traps and checking vents.
Will running water fix it?
Sometimes. Filling traps often stops sewer gas from entering living space if dry traps are the cause.
Can my HVAC cause the smell?
Yes. Negative pressure from furnaces or exhaust fans can pull gas from drains if traps or vents aren’t working properly.