The Types of Air Admittance Valves and Their Uses

Air admittance valves allow air into a drainage system to prevent negative pressure from disrupting wastewater flow.

They replace the need for traditional vent pipes that extend through the roof, making them a space-saving and cost-effective solution for modern plumbing.

Different types of air admittance valves are designed for specific applications. This guide will explain the main types, their uses, and how to choose the right one for your plumbing system.

How Air Admittance Valves Work

FloPlast’s air admittance valves have an A1 rating, meaning they can be installed below the flood level of connected appliances, provided they comply with BS EN 12380: 2002.

So, when water flows through a drainage pipe (such as 110mm drainage pipes), it creates negative pressure that can siphon water from traps, allowing sewer gases to enter a building.

An air admittance valve opens to let air into the system, balancing the pressure and preventing siphoning.

Once the pressure stabilises, the valve closes to stop odours from escaping.

These valves are often used when traditional vent pipes are impractical due to space limitations or structural constraints.

If you’re looking for more detailed information, check out our guide on how to use an air admittance valve.

Types of Air Admittance Valves and Their Uses

Not all air admittance valves are the same, and each type is designed for specific conditions.

Here are the most common ones and where they are typically used:

1. Standard Air Admittance Valve

Best for: Sinks, basins, bathtubs, and small residential drainage systems

The most commonly used type in homes.
Installed on branch pipes to vent individual fixtures or small groups of fixtures.
Ideal for bathrooms, kitchens, and laundry rooms where traditional venting is difficult.

2. External Air Admittance Valve

Best for: External AAVs are generally designed for indoor use, but Building Control may approve them for outbuildings or detached garages in some cases. Always check local regulations before installing an air admittance valve externally.

Made from durable, weather-resistant materials.
Suitable for detached structures that require proper drainage venting.

3. Mini Air Admittance Valve

Best for: Dishwashers, washing machines, and small appliances

Compact and designed for tight spaces.
Used for appliances that require venting but don’t need a full-size valve.
Helps maintain proper drainage flow in small-scale plumbing setups.

Choosing the Right Air Admittance Valve

FloPlast’s air admittance valves comply with BS EN 12380: 2002 and carry the British Standards Kitemark (KM512474), ensuring they meet industry standards for performance and reliability.

The right choice depends on the size of the drainage system and the installation conditions.

For single sinks or bathroom fixtures: A standard valve is usually sufficient.
For detached garages, sheds, or outbuildings: An external valve is the best option.
For small appliances: A mini valve provides a compact solution.

Always check local plumbing codes before installation, as regulations can vary.

Advantages and Limitations of Air Admittance Valves

Advantages:

Reduces the need for traditional vent pipes – Simplifies installation and lowers material costs.
Prevents roof penetration – Avoids the need to cut through the roof, reducing the risk of leaks.
Saves materials – Requires fewer pipes, fittings, and installation components.
Reduces labour costs – Fewer pipes and connections mean quicker, easier installation.
Space-saving – Ideal for renovations and areas where traditional venting isn’t possible.
Flexible installation – Can be placed inside walls, under sinks, or in other concealed areas.

Limitations:

Not always approved by building codes – Some areas have restrictions on their use.
Mechanical parts can fail over time – Unlike traditional vent pipes, these valves have moving components that can wear out.
Limited lifespan – They may need to be replaced after several years.

Conclusion

Air admittance valves offer a practical solution for venting drainage systems when traditional vent pipes aren’t feasible.

Whether you need a standard valve for a sink, an external option for outdoor use, or a mini valve for appliances, choosing the right type ensures proper drainage and prevents plumbing issues.

Before installation, always check local regulations to ensure compliance. When used correctly, these valves improve plumbing efficiency and reduce installation costs.