Habitation Investigation

What are air admittance valves?

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The drain-waste-vent system (DWV) often employs a mechanical vent, also known as an air-admittance valve or AAV. Although they may function as intended, AAV’s are a mechanical component, and as such, they are subject to failure over time. When an AAV fails, it can lead to issues such as inadequate venting, sewer gas odor, or even wastewater backup. Therefore, it is important to regularly check if an AAV is not functioning properly. Air admittance valves are more commonly seen on newer homes, new construction and in an older home that has had some improvements made.

It is also essential to follow manufacturer instructions when installing AAV’s to ensure they are correctly placed and working effectively.

Failure of these mechanical vents may allow sewer gases to escape into the attic or living space, which would result in potentially hazardous and unhealthy conditions. If, at any time, you notice an odor consistent with rotton egg smell, waste or sewage, you should immediately contact a qualified plumber to evaluate the AAV’s.

How an air admittance valve works.

An air admittance valve (AAV) is a simple mechanical device designed to allow air to flow into a drainage system to prevent wastewater from being siphoned out of traps or allowing sewer gases to escape into a building’s interior. The AAV is typically installed beneath plumbing fixtures or appliances, such as sinks, toilets, and dishwashers.

When wastewater flows out of a plumbing fixture, it creates a vacuum within the drainage system. This vacuum can cause traps to become empty, allowing sewer gases to flow back into the building. Additionally, siphoning can occur when a large volume of wastewater drains out of a fixture, which pulls water from nearby traps, causing them to empty and allowing gases to enter the building. An AAV automatically opens to allow air into the drainage system, which prevents siphoning and ensures that traps remain full of water, blocking the entry of harmful sewer gases.

The AAV works by using the pressure of the wastewater flowing through a pipe to pull open a valve that allows air to enter the drainage system. The valve opens when negative pressure (vacuum) is exerted on the valve; this changes the position of a floating ball or diaphragm, allowing air to flow into the system. The valve then closes when the wastewater flow stops or when the pressure within the drainage system returns to equilibrium.

Overall, an AAV is a simple and effective solution for preventing wastewater siphoning and harmful gases from entering a building’s interior. It is a low-maintenance device that does not require power, and it helps ensure that plumbing systems function safely and effectively.

For information on how to protect your plumbing during the winter, here is an article on winterizing your outdoor faucets.

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