In a typical gravity septic system the roof vent is the high vent that draws air through the 6" of system sand and 4-12" of topsoil cover on the leach field.
Gravity systems with more than 18" of cover, under paved surfaces or with Multi-LevelTM configuration require only the addition of a low vent, since the roof vent will still function as the high vent.
Pump system pressure lines separate the leach field from the roof vent and require installation of a high vent at the distribution box and a low vent. This type of venting is referred to as differential venting. The use of high and low vents replicates the vertical "chimney" effect to pull air through the leaching system, ensuring adequate oxygen to the biomat around the Enviro-Septic® pipe. The low "inlet" vent must always be installed at the end of the leach field. If installed inside the distribution box freezing may occur. All vent systems must have only one low "inlet" at the end of each line, section or basic serial bed and one high "exhaust" at the roof vent or at the distribution box. No other vent or opening may be placed between the high and low vents. The high vent must be at least ten feet above the low vent.
The low vents may be covered with a bird bath, fiberglass rocks/granite hitching posts, etc., or remotely located. High vents could be incorporated into a flag pole or a remote location near trees or a building.
A remote vent location must ensure that condensation does not collect in the connecting pipe and block air passage. The connecting line invert must be above the top of the highest Enviro-Septic® line and, if applicable, above the top of the distribution box. The connecting pipe must slope back towards the system or all low points must be above seasonal high water and drilled to drain into a gravel cavity. (see diagram below)
Venting Requirements
General rule
Low and high vents are required of all systems to ensure that air is drawn completely through the entire Enviro-Septic® system. However, if the system is a gravity system where air flow is not restricted, no low vent is needed unless it is a State requirement or the system is under more than 18" of cover. Please reference your State manual for specifics. No additional vents may be located between the high vent and low vent. The opening of the high vent must be at least 10 feet above the opening of the low vent. High vents must provide at least the same flow capacity as low vents. Connections within the system must also have similar flow capacities.
Purpose:
Venting design, installation, and maintenance must ensure that every linear foot of Enviro-Septic® pipe in all serial beds, sections, or lines receives oxygen to accommodate natural biologic activity.
Low vent locations
Low vents are installed through an offset adapter at the end of each
serial system or bed
section of a combination system
line of a distribution box system
High vent locations
High vents are installed in a variety of locations based on the system design.
The roof vent will function as the high vent if there are no pumps, restrictions, or other vents between the low vent and the roof vent.
If a restriction is placed between the low vent and the roof vent, a high vent is required through an unused distribution box outlet.
In pumped systems a high vent is required through an unused distribution box outlet.
High vent on D-Box
This diagram shows a high vent installed in a D-Box. This configuration is required in pumped systems or when other restrictions or vents are installed between the low vent and the roof vent.
