Commercial Sewer Odor Diagnosis, Step by Step

A sewer odor in a restaurant, office or apartment building has several common causes, and they are not equally likely or equally involved to find. The sequence below runs from the quickest and most common to the most involved. Skipping to the camera first is how a building ends up with a video of a healthy pipe and the same smell.

Sewer gas smells like rotten eggs, and so can a natural gas leak or a drain full of food waste. A natural gas smell is an emergency: leave and call your gas utility. If it is sewer, note when and where it shows up. A smell that appears after a weekend or in a rarely used restroom points to a dry trap. A smell near the kitchen suggests grease. A smell that follows the air handler is a different problem. See how to find the source of a sewer smell step by step and what a property manager should log.

This is the most common cause in commercial buildings, and the cheapest test. Pour water into every floor drain, floor sink and seldom-used fixture and see if the smell stops. Code requires a 2 to 4 inch seal, and says a seal that can evaporate has to be protected. A floor drain with no primer can dry out. Check whether each drain has a primer, which kind, and whether it works. A hand sink drain connected to a floor drain in the same room counts as protection under the code, but only while it is in use. See why floor drains dry out so fast in Arizona and trap primers for commercial floor drains.

A toilet with a failed wax ring or loose flange leaks gas at the floor. A grease interceptor that is full or has a poorly sealed lid is an odor source of its own. In a restaurant, look at the lid and its last cleaning date before blaming the lateral. See toilet wax ring sewer smell and grease trap smell: when is it full. HQ does not pump interceptors. A licensed hauler does, and we repair and inspect the tank afterward.

If the traps are wet and the fixtures are sound, the gas is coming through a crack, an open joint or a vent. That is the job for a smoke test. Every drain is filled first, as EPA directs, then smoke goes into the system and we watch the roof, the interior and the exterior. Smoke at a roof vent is normal. Smoke anywhere else is the path. HQ uses liquid-smoke equipment that forces air into the vent system. See commercial sewer smoke testing, plumbing vent smoke testing and restaurant sewer odor smoke testing.

If smoke finds nothing and the smell remains, the leak may be buried where smoke has no path to the surface. EPA notes the surface exit is not always the underground leak, and a crack in soil or under a slab can hide. A camera looks inside the pipe for cracks, offsets and bellies. If grease or scale hides the pipe wall, the line is cleaned first so the camera can see. See commercial sewer camera inspection and sewer smell from a cracked line under the slab.

Your nose is a good first alarm and a poor instrument. OSHA's data show the smell of hydrogen sulfide fades at 100 to 150 ppm, which is far above the workplace ceiling limit. A strong smell with dizziness, headaches or eye irritation is a reason to ventilate and leave, not to keep investigating. See when to evacuate over a sewer smell and do sewer gas detectors work.

If the drains are backing up, you have a stoppage and the first step is clearing it. If the odor is only at one fixture and goes away with water, you have your answer in step 2. If it rides the air handler, the source may be outside the plumbing. Plumbing is our work, not HVAC.

Call with the building, where the smell is and when. HQ offers 24/7 emergency service, free estimates and an upfront price before work starts. See smoke testing, sewer camera inspection and commercial drain cleaning.