The following failures in the plumbing system may allow sewer gases to flow back into a building:
- dried-out piping and plumbing fixtures. In most cases, intruding sewer gases are caused by a loss of the water barrier where traps have gone dry. Especially in dry weather, infrequent use of a toilet, shower or floor drain can allow for rapid evaporation and entry of sewer gases into the living space. Particularly common culprits are floor drains placed in locations where they are likely to dry out, such as near water heaters or furnaces, as well as seldom-used drains, such as those in janitor’s closets, workshop areas and mechanical rooms. Homeowners can maintain the water barriers by using the fixtures more often or by pouring water down the drains. Automatic drain-trap primers may also be installed so that a small amount of water is periodically delivered;
- cracks in the plumbing drain line or vent pipes. A water leak typically accompanies a crack in the drain line, but vent pipe cracks are more difficult to diagnose, and they can vent a large quantity of sewer gases into the home. Plumbers can locate these cracks by using a special machine that generates artificial smoke and pumps it into the plumbing drain system. The smoke pressurizes the system and exits through any cracks or loose fittings;
- diffusion from a leach field septic system;
- through cracks in a building’s foundation; and
- plumbing vents installed too close to air intakes or windows in homes equipped with HVAC air handlers that admit outside air for ventilation. Wind and air flow around the building can allow for sewer gas to enter the building even where plumbing vents and air intakes are appropriately placed. Homeowners can add vent pipe filters or alter the height of vents to alleviate the problem.