AIR ADMITTANCE VALVE
                        What does the code say?
1. Must be  installed per code and manufacturer's installation instructions. 
2.Permitted for individual vents, branch vents, circuit vents and stack vents.
3. Shall be located 4-inches above the horizontal branch drain or fixture drain being served.
4. Must be 6-inches above attic insulation 
5. Access shall be provided 
6. Shall be sized accordingly
7. Within each plumbing system, a minimum of one stack vent or vent stack shall extend outdoors to the open air.

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One-way valve design to allow air to enter the plumbing drainage system when negative pressures develop in the piping system. The device shall close by gravity and seal the vent terminal at zero differential pressure (no flow conditions) and under positive internal pressures. The purpose of an air admittance valve is to provide a method of allowing air to enter the plumbing drainage system without the use of a vent extended to open air and to prevent sewer gases from escaping into a building.

1. All individual, branch and circuit vents shall connect to a vent stack, stack vent, air admittance valve or extend to the open air.

2.  Where permitted. Individual, branch and circuit vents shall be permitted to terminate with a connection to an air admittance valve. The air admittance valve shall only vent fixtures that are on the same floor level and connect to a horizontal branch drain. 

3.  The horizontal branch drain shall connect to the drainage stack or building drain a maximum of four branch intervals from the top of the stack.

4.  The horizontal branch shall be provided with a relief vent that shall connect to a vent stack, or stack vent, or extend outdoors to the open air. The relief vent shall connect to the horizontal branch drain between the stack air building drain and the most downstream fixture drain connected to the horizontal branch drain. The relief vent shall be permitted to serve as the vent for other fixtures. Sizing of relief vent shall comply with the adopted code.

5.  The air admittance valve shall be located a minimum of 4 inches 9102 mm) above the horizontal branch drain or fixture drain being vented. The air admittance valve shall be located within the maximum developed length permitted for the vent. The air admittance valve shall be installed a minimum of 6 inches (152 mm) above insulation materials.

6.  Access shall be provided to all air admittance valves. The valve shall be located within a ventilated space that allows air to enter the valve.

7.  The air admittance valve shall be rated in accordance with the standard for the size of the vent to which the valve is connected.

8.  Within each plumbing system, a minimum of one stack vent or vent stack shall extend outdoors to the open air.

9. Prohibited Installations

Air admittance valves shall not be installed in non neutralized special waste systems as descried in Chapter 8. Valves shall not be located in spaces utilized as supply or return air plenums.

NOTE: Please refer to the current edition of the applicable building code for your area. 

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How We Used to do IT:
                                              LOOP VENTING ( still acceptable)


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