Types of Plumbing Vents: What You Should Know

Understanding the types of plumbing vents is key to keeping your plumbing system running smoothly. Vents are essential to your home's drainage system because they let air into the pipes. This keeps the pressure from building up and keeps sewer gases from getting inside. As the owner of All Needs Plumbing, I’ve seen firsthand how proper venting saves homeowners from costly repairs and stinky surprises. Let me walk you through the main types of plumbing vents you’ll encounter and why they matter.

Why Plumbing Vents Matter

Plumbing vents balance air pressure in your drainage pipes. Without them, water can’t flow freely, and traps under your sinks or toilets might lose their water seal, letting sewer gases into your home. I once had a client whose toilet bubbled and smelled foul because their vent was blocked. Fixing the vent cleared the problem instantly. That’s why vents are not just pipes sticking out of your roof—they’re vital for your health and comfort.

Pro-Tip: When you’re renovating or adding new fixtures, it’s tempting just to connect everything to the existing plumbing. But your current venting system might not be designed to handle extra fixtures. Overloading vents can cause poor drainage and sewer gas issues. 

A licensed plumber will examine your system to ensure the vents are the right size and in the right place for the new setup. This step is crucial because it ensures your plumbing remains efficient and compliant with Australian standards. Don’t skip this check—it’s a small investment that prevents headaches later.

Main Types of Plumbing Vents

True Vent (Stack Vent)

This is the classic plumbing vent you see poking through the roof. A vertical pipe connected to your drain system vents sewer gases safely outside. True vents are the backbone of most plumbing systems and keep air flowing to prevent pressure issues.

Air Admittance Valve (AAV)

Also called Studor vents, these mechanical valves let air into the system but block sewer gases from escaping. They’re handy when roof venting isn’t possible, like in interior bathrooms or kitchen islands. AAVs are compact and easy to install, but have moving parts that may need replacement over time.

Wet Vent

Wet vents serve two purposes: they carry wastewater and provide ventilation. For example, a bathroom sink and toilet can share a damp vent, saving space and materials. This setup is common in Australian homes but must be installed carefully to meet plumbing codes.

Loop Vent

Loop vents form a loop under fixtures like island sinks where traditional venting isn’t practical. They connect back to the main vent system, preventing sewer gases from escaping. Loop vents are a clever solution for tricky layouts.

Common Vent

Common vents, such as back-to-back sinks, serve two fixtures on opposite sides of a wall. They connect both fixtures to a single vent pipe, reducing the number of roof penetrations and simplifying your plumbing.

Circuit Vent

Circuit vents are used mainly in larger buildings. They connect multiple fixtures in a loop, maintaining proper air pressure across all drains. They are more common in apartments or commercial settings.

Pro-Tip: If you notice your toilet gurgling or your drains are slow, it’s often a sign that your plumbing vents aren’t working correctly. Gurgling sounds happen because air is struggling to enter the drain pipes, causing negative pressure that pulls air through the water traps. This can also lead to slow drainage as the water flow is disrupted. 

If you don't pay attention to these signs, they could lead to bigger problems like sewer gas leaks or clogged pipes. The best move is to call a professional plumber when you notice these symptoms. Getting help early can save money and keep your home from smelling bad.

FAQs About Types of Plumbing Vents

Can a shower and toilet share a vent?

Yes, a shower and toilet can share a vent through a wet vent setup. This means the vent pipe also carries wastewater from one fixture while providing air flow for the other. It’s a space-saving and cost-effective solution often used in bathrooms. 

However, the installation must follow plumbing codes to ensure the vent size and slope are correct. Improper wet venting can cause slow drainage or sewer gas leaks, so it’s essential to have a licensed plumber handle this.

Should each toilet have its vent?

Ideally, each toilet should have its dedicated vent to guarantee proper air circulation and drainage. Toilets produce a large volume of wastewater, and insufficient venting can cause slow flushing or trap siphoning. 

However, if designed correctly, some plumbing codes allow shared vents, such as a standard vent serving two back-to-back toilets. The key is proper sizing and layout—something only a professional can verify. If you’re unsure, having a plumber inspect your system is best.

How many drains can share a vent?

The vent pipe's diameter, the drain pipes' size, and local plumbing codes all affect how many drains can share a vent. For example, a 50mm vent pipe might serve several fixtures in a small bathroom, but larger systems need bigger vents or multiple vent pipes. 

Overcrowding a vent can cause poor air flow, leading to slow drainage and sewer gas problems. A licensed plumber will calculate the correct venting for your home’s layout to keep everything working smoothly.

How do I know if my toilet is appropriately vented?

You can often tell if your toilet is vented properly by observing how it flushes. A properly vented toilet flushes quickly and quietly without gurgling noises or water backing up. The vent might be blocked or undersized if you notice bubbling in nearby drains or a slow flush. 

Another sign is unpleasant sewer odours in the bathroom. If any of these happen, it's time to call a professional plumber to inspect and fix your venting system.

What happens if a toilet is not vented properly?

When a toilet isn’t appropriately vented, several plumbing issues can arise:

Slow drainage

Water can't flow smoothly without air entering the pipes, causing backups.

Trap siphoning

The water seal in the toilet trap can come loose, letting sewer gases into your home.

Unpleasant odours

Sewer gases escaping into your bathroom create health hazards and discomfort.

Damage to pipes

Negative pressure can stress the plumbing, potentially causing leaks or pipe damage over time.

These problems affect your home’s hygiene and comfort, so prompt professional repair is essential.

Additional Benefits of Proper Plumbing Venting

Proper venting improves water flow, reduces clogs and backups, and prevents harmful sewer gases from entering your home. It also extends the lifespan of your plumbing system by reducing stress on pipes and fixtures. Knowing your plumbing is safe, efficient, and up to code gives you peace of mind.

If you want to learn more or suspect your plumbing vents aren’t up to scratch, we’re ready to help. All Needs Plumbing offers a $0 callout fee, so you only pay if we fix the problem. Our team provides 24/7 same-day service because plumbing issues don’t wait for business hours. We offer seniors a 15% discount and $150 off hot water system installations.

Don’t risk DIY fixes for your plumbing vents—let our licensed experts handle them safely and efficiently. Contact us today, and we’ll make sure your plumbing vents keep your home fresh and flowing.

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