What Are Plumbing Vents And Why Do You Need Them?

Plumbing vents, often known as vent stacks or plumbing air vents, are key components of a plumbing system. Interestingly, these vents don’t involve water. Rather, plumbing systems include drainage and ventilation parts. A plumbing air vent is typically a vertical pipe extending through your roof. This setup allows air to enter and helps vent out odours and gases, keeping your drainage system running smoothly.

What Is The Purpose Of A Venting System?

Plumbing vents have two primary purposes:

1. The plumbing vent helps regulate the air pressure within the plumbing system. It holds the airflow in your plumbing system, ensuring waste and water flow through the drain pipes that drain out of your house. It prevents a vacuum that causes slow or no drainage. Each plumbing fixture in your home requires air to move the water through the drainage pipes. Clean drain pipes can only do their job when the vent pipe works.
2. A plumbing vent system removes sewer gases, allowing them to escape and providing an entry point for fresh and clean air into the sewer system.

It’s not unusual for gases to seep from the sewers into your house. These gases, like methane, hydrogen sulphide, and others, often smell unpleasant and can be quite hazardous.

Plumbing vents help fresh air circulate while whisking away unpleasant odours and sewer gases from your plumbing. This keeps your home smelling fresh by dealing with what flows through your pipes and sewer lines. Therefore, a clogged plumbing vent is not something to take lightly.

P-Traps

Every drain in your home’s plumbing system makes use of traps.

P-traps are a modern invention that holds a small amount of water and prevents sewer gases from infiltrating your home. They can also trap debris and prevent clogs. They can also hold valuables like wedding rings, necklaces, or other small prized belongings.

Traps and vents must work together. Under AS/NZS 3500.2 (the national sanitary plumbing and drainage standard, which specifies vent termination heights, air admittance valve (AAV) placement, and minimum vent sizing to protect water trap seals), an adequately vented drainage system prevents negative pressure from siphoning water from traps. This ensures water seals remain intact and stops noxious sewer gases from infiltrating living spaces.

Vent Pipe System Specifications

Many plumbing codes define where a vent should connect to a fixture. Typical examples are more than 150 mm above the fixture flood rim level.

The vent stack should lead from the main bathroom to the outside and extend at least 300 mm to 600 mm above the roof surface, with clear separation from windows and outdoor areas.

The diameter of this vent pipe should not be smaller than DN 50 to DN 65 if serving multiple fixtures, while a DN 100 main stack vent is typically required to serve an entire residential household.

The vent stack is the central vent; other attached vents, like a tree trunk and branches coming off it, can be smaller.

The smaller vents can be installed horizontally to reach the fixtures they serve. However, many are sloped, which helps airflow work better in the system. Plumbing codes usually define how sloped these must be.

Types of Plumbing Vents

Here are the different types of vent pipes and where you can find them:

1. True vent: A vertical pipe attached to your drain line is the most common vent type. Because no water runs through it, it vents from the roof.
2. Common vent. Used between two fixtures installed on opposite sides of a wall, like back-to-back sinks. They’re linked to the stack with a sanitary cross.
3. Auxiliary vent: Attached to the drain line or behind the plumbing fixture, it runs up and over to the roof’s central vent.

Special Venting Systems

You may need a particular type of vent for your specific system. Here are a few examples:

1. Circuit Vents - Places with many fixtures, such as apartments and buildings, may need a circuit vent system. They can minimise the number of exit points required for the many vent stacks of regular vent systems. Each horizontal vent in a circuit system can be connected to up to eight fixtures. You can combine many circuit vents, which works well in large buildings.
2. Chicago Loop - These are for some fixtures with specific configurations and are incompatible with standard vents. For example, some kitchen islands feature a drain line that cannot run horizontally above floor level. Using a Chicago loop can be the answer. A Chicago loop sees a vent pipe connected under the sink to create a circle above the sink’s floor rim, leading right down into the kitchen’s floor. Then, the pipe can extend horizontally to connect with the main vent pipe.
3. Studor Valves/Air Admittance Valve, Rather than using a standard vent for your sink drain, you can use a stud or valve. Check your local regulations about these valves, as they cannot be used everywhere. When water drains down through your sink drains to the pipe, the valves open, allowing air in and releasing pressure building up in the pipes. The downside is that they can get stuck closed and wear out quickly.

What Are the Signs Your Plumbing Vent Pipe Is Blocked?

A blocked vent can cause negative pressure in the plumbing system, disturbing water flow. Watch for these tell-tale signs:

• Water is draining very slowly when you have a blocked vent.
• Clearing the drain is ineffective.
• It smells potent, like sewage, coming up through the drain. If this happens, your P-trap has likely emptied due to negative pressure.
• Gurgling sounds are coming from your drains and pipes, with water coming from another drain. The sound happens when air gets sucked out of your P-trap.
• Stagnant water is sitting in your bathtub, sink or other drains.

Keep Your Plumbing Vents Unblocked

How you clear your vents hinges on the cause of the blockage. The ideal way to identify the obstruction is by using a CCTV drain camera. Our skilled technicians, such as those at Fixed Today, perform this service.

We offer top-notch plumbing services, deploying advanced cameras into your drains. This gives us live visuals of your drain system, enabling us to tailor solutions to your plumbing issues.

It will also confirm something wrong with your vents or if the issue is related to something else.

Working on roof vents, main drainage stacks, and concealed venting systems involves significant height hazards and strict technical requirements under AS/NZS 3500.2. Attempting DIY fixes can inadvertently damage roof flashing, break vent seals, or exacerbate siphonage.

For safe, dependable assistance, turn to the licensed drainage specialists at Fixed Today. Sydney homeowners have trusted and returned to our team across decades (proudly serving the community since 2011) for comprehensive drainage diagnostics. Operating under NSW Fair Trading Contractor Licence 305428C with Qualified Supervisor oversight, we use CCTV cameras and pressure testing to quickly identify whether a venting defect, birds’ nest obstruction, or underground blockage is affecting your fixtures.

When you contact us, our team asks a few quick questions about your roof design, storey height, and gurgling symptoms so our truck arrives equipped with roof safety harnesses, inspection cameras, and matching vent cowl fittings. On site, our plumbers clearly explain the root cause and provide a transparent task breakdown with upfront pricing before starting. Contact Fixed Today to restore proper airflow and drainage to your home.