Air admittance valves are mechanical valves operated by the pressure of wastewater in a plumbing drain, waste and vent system. They are typically made of plastic and can be installed using regular, chemical plastic welding techniques, without the need for additional tools.
Air admittance valves must be installed in accordance with local building codes and manufacturers' recommendations. They should be installed vertically, rather than horizontally, in an inside location that is easily accessible.
Air admittance valves should not be installed outside a building because of the risk of freezing and if they are installed in a ventilated loft or attic space they should be insulated. They should be fitted above the overflow level of appliances.
When closed, air admittance valves prevent the escape of hydrogen sulphide, ammonia, methane and other components of sewer gas. Take care not to contaminate the sealing surfaces of the valve during installation; contamination may make the valve less airtight when closed.
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