Septic Problems - Septic Smell in House

Septic Smell, Odor or Gas Inside Your House

WARNING: Gases from the septic system can be explosive.

Septic smell, odor or gas inside the house is a health and safety risk.  Septic smell (odor) can also be confused with the odorants used in natural gas or propane.  If you smell odors in your house, pay attention to where you smell them and open windows or doors to vent the gas out of the house.  If your home has propane or natural gas fixtures (heaters, stove, oven, etc.), call your gas company immediately.  Your gas company should provide rapid response to make sure you do not have a gas leak. 

You have confirmed there is no propane/natural gas leak and the odors persist.  In this case, your plumbing drains may have a venting problem.  In a properly plumbed building, the sewer drains are connected to a vent pipe through the roof.  Sometimes more than one vent is required.  The roof vents allow the septic gas (odor & smell) to escape so there is no build-up of potentially dangerous gas in your house or septic system.

Causes of Septic Smell In the House

There are various problems which may cause septic smell, odor or gas inside your house.  Some common problems we have seen include:

  • There is no vent pipe through the roof.  Typically, this means that the highest point in the drain plumbing is a pipe that dead-ends inside the attic or inside a wall.  In this case, a licensed plumber is required to modify your plumbing so that septic system venting is consistent with code.
  • There is a vent through the roof, but the flow of septic gas (smell & odor) is obstructed.   Sometimes the obstruction can be easily removed; such as an insect nest near the top of the roof vent.  Other times the obstruction may be more difficult to locate.  For example, the interior vent piping may have a horizontal run (inside a wall) before going up vertically through the roof.  The horizontal drain piping can develop a low point that fills with water (from condensation).  The water can effectively block the venting. This situation can be very difficult to diagnose because a pipeline snake does not find a solid obstruction.  A plumber may be able to use a pipeline camera to identify the location of this problem.   This problem is fixed by providing a slope to the horizontal run so that any condensation drains to the septic system.
  • Improper plumbing modifications.  Home re-modeling can often result in relocating plumbing fixtures (toilets, sinks showers, tubs, etc.).  If the drain connections from the former fixtures are not properly sealed, the former drain connections provide a route for septic smell, odor & gas to escape into the house. 
  • Septic smell emanating from a sink or tub drain is a common problem with seasonal residences.   All of your interior plumbing fixtures (sinks, tubs, and toilets) should have a trap, a goose-neck in the drain piping.  Normally, this trap has water in it.  The trap water blocks the septic gas from venting into the house through the drain.  If a fixture like a sink is not used for a long period of time, the trap water may evaporate.  A dry trap allows the septic gas to move through the trap and into the house.  This is probably the easiest problem to fix.  Pour some water into the drain.  This will re-establish water in the trap and prevent the septic gas (smell & odor) from entering the house.

You may also want to read our section on Advanced Septic Venting and Odor Control.