Information About Plumbing Vents

Plumbing Vents

Plumbing vents play a significant role in an indoor plumbing system. However, many people outside the plumbing industry do not know about plumbing vents. It is important to have basic understanding of plumbing vents to ensure adequate plumbing maintenance.


A building’s plumbing system is made up of three parts:

– The venting system

– Drainage system

– Waste system

The drainage system consists of pipes that carry wastes from the sink and shower drains. The waste systems consist of pipes carrying wastes from the sink and shower drains. This prevents wastes from the toilet from backing up into sinks and bathtubs in case of a blockage.

Plumbing vents consist of pipes that drain wastes outside the building. In most cases, plumbing vents drain through the roof. Plumbing vents have two functions:

1. To divert sewage gases out of the building.

2. Equalise pressure in plumbing pipes when water flows out of a drain.

Without plumbing vents, gasses and bacteria will build up in septic tanks. The vents prevent the bacteria and gasses from the septic tank from being released into the house. Plumbing vents let sewer gases out of buildings. This prevents wastewater from going back into drains and toilets.

Toilet flange firestop and piping firestops. T...
(Photo credit: Wikipedia)


A London-based cabinetmaker known as Joseph Bramah is credited with inventing the water closet in 1778. The greatest flaw with the design of the first flush toilet is that the plumbing did not have a vent. This made gasses to build up in the first water closets with fatal results in some cases. Four years later, a solution to this problem was found.

In 1782, John Gallait invented the stink pipe. Nearly all improvements in toilet designs are based on John Galliat’s stink pipe.


The easiest way to understand the significance of plumbing vents in a building is to imagine draining a bottle of soda. If you hold the bottle at a -degree angle, the soda will not drain properly. This happens due to build-up of negative pressure inside the bottle. The negative pressure builds up because there is nothing to replace the soda flowing out. Punching a hole at the top of the bottle allows air to be drawn into the bottle equalising the pressure hence making the soda flow freely out of the bottle. Plumbing vents can be equated to the hole at the top of the bottle.

Plumbing systems that don’t have any of introducing air into the systems end up having negative pressure inside the system, which prevents water from draining out of the pipes freely. In addition, vents allow gasses from decomposing materials to escape out of the building so that it does not build up and cause foul smell to permeate throughout the building.

Improper installation of plumbing vents can cause many problems. Odours from the sewage system in a house or building are signs of a leaking vent. Slow drainage and funny sounds from the drainage may indicate a blocked plumbing vent.

Professional plumbers can easily diagnose the problem. However, doing your own investigation will not hurt. Leaks around plumbing traps, moisture under sinks may be signs of problems with the plumbing system. Check laundry sinks, toilets in the bathroom, toilets in empty apartments and clogged traps. Find out if an odour is coming out of these areas.


Most vent pipes exit through the roof or attic. Countries have different specifications for the size of the pipe to be used as plumbing vents. The specifications can be found in the local health codes under sanitation. In most countries, new plumbing fixtures including tubs, toilets and sinks are required to meet code specifications. These requirements are important to protect the health of building owners, residents and the community.

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Scott Matthews works as a plumber for Belfast Plumbing Services. He likes to blog about all plumbing to help the public learn to do the smaller jobs themselves.

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