Automatic Venting Great Device or Not?

Common Plumbing Code Violation Drain Venting

Air Admittance Valves (AAV) and Mechanical Vents

Why do we need Venting on drain lines and What is it?

 Without venting, our drains would hardly work, and they would make gulping noises due to negative air pressure in the lines.  When water moves down our drains the empty space that was filled with air now needs to be replenished with more air.  Our drain system can be related to a full bottle of water being emptied.  If we take the cap off of the bottle and turn it upside down to empty the bottle, we will notice 2 reactions occurring.  

1.      The bottle creates a vacuum which sucks air into the bottle to help drain the water more quickly.  We will feel the bottle jump and make a gulping noise while the water is draining.

 We will notice the bottle being pulled together at the top where the air is replacing the water.

v  The reason the bottle starts to gulp air inside is because we are creating negative pressure.  By tipping the bottle completely upside down we close off its only entrance for air or water to pass through.  The bottle is trying to replace the area that was once occupied with water for an exchange of air.  The reason the bottle actually jumps and gulps has to do with the amount of water that is trying to be released.  We can refer to the water pressure caused by the gravity as head pressure.   The amount of head pressure blocking the outlet of the bottle will determine how much velocity and force it takes to make the bottle jump.

v  The bottle is being squeezed together at the top while draining because of negative air pressure in the bottle.  Negative air pressure is created when a closed room or container is being deprived of the air inside of it.  Referring back to our plastic bottle example, the plastic is ductile so it makes the bottle suck together where it is lacking air.   

Click here to check out what happens when you improperly vent a tanker car, this is an extremely interesting example of what kind of force negative pressure can have.

These are major concerns with the venting of your drain pipes.  Another concern is the added pressure when drains tend to back up.  Vents also allow for another place for drain pressure to escape.  Sometimes when a home’s drain line backs up, it will push the water or sewage through the main vent stack.  This may cause the water to come out of the stack opening on the roof.  This would be referred to as positive air pressure.

Venting allows for the air in the line that is being filled with water to be replaced immediately with more air.  This will sustain a neutral air pressure which will allow your drains to work properly.  Properly working drains always keeps a sufficient amount of water in the traps.  Drain traps are extremely important without them sewer gas would be present in our home.  The sewer gas is terrible for anyone’s health and should not be breathed in.  Without proper venting the water that is supposed to be in the trap may be siphoned into the line in order to change the negative air pressure back to neutral.  An absence in water leaves the line wide open to your homes main sewer line, this is where the sewer gas will enter your home.

Air Admittance Valves (AAV) or Mechanical Vents

AAV’s or Mechanical vents work on a spring loaded valve that will let air in.  When positive pressure comes up through the line it closes up tightly, not letting any water or air escape.  These devices are basically check valves that only allows air to be sucked into the system.

Most of the time we see these devices underneath the sink in the vanity or buried in the wall.  The technology has developed significantly over the years.  With new technology and extensive testing, a more reliable product has been developed. 

Mechanical Vent was the original term for these devices.  I feel the term has been changed to AAV so that people will use them.  Changing the name has confused many when trying to decipher the plumbing codes.  A Mechanical vent is the same as an Air Admittance Valve in all code books. 

Why someone might use a AAV?

Sometimes you may run into a situation were the main vent stack or any branch vents are no were close to where you want to put a sink, toilet, or shower.  This makes it possible to vent your drains in the hardest spots.  You also may have existing piping or HVAC Ducts in the ways of here you need to run your vent pipe.   AAV’s gives you a cost effective solution to adding or moving your drains. 

Some plumbers and home owners find this to be an amazing product to complete their task.  But the best plumbers will complete your job the right way the first time, so you will never have any unexpected issues later down the line.

Are AAV Compliant to Code?

The simple answer to this is “No”.  In the state of Illinois, the code strictly permits against the use of a mechanical vent or AAV.  As far as code goes for Residential and Commercial work you will want to check with your Local Municipal Inspectors. In some cases, the village may allow the use of this device.  You must know that every city is slightly different with their codes but in most cases throughout the United States they are not allowed and should not be allowed.  Let’s take a look at what venting systems are used by the best Plumbing Companies.

Difference between a dry and wet vent

A Dry vent is a simple one drain system where the vent will not serve as another’s drain.

 

A wet vent will tie into another fixtures drain, thus the term wet drain.  A wet vent may share a common vent stack but will tie in at different heights. 

v  A simple example of a wet vent would be a bathroom were the main vent stack is offset to one side of the room.  The toilets drain will run directly to the main stack were it goes out to the sewer and is vent from the stack that goes to the room.  Now the sink will run a vent branch up to the stack and the drain will tie into the toilets drain pipe before the toilet vents in the stack.

Types Plumbing Venting

Common Vent/Drain System

A common venting system is where drain lines tie into the main stack at different places on the main stack.  These drains use the stack as the vent and drain pipe.  They may be back to back drains on one floor or multiple drains on different floors.

Branch Venting

Is extremely common in homes it is were drains share a branch vent pipe which ties into the main stack.

Loop Venting 

The vent goes up and loops back down and ties back into the drain line for the fixture.  Commonly only used for sinks.  This system is normally allowed for single sink systems like in a kitchen island where it is impossible to tie into a vertical stack.  Some Municipalities allow one loop vent per house.  Before the loop vent ties back into the drain it can either branch off to be properly vented or not.

Circuit Venting

Circuit venting is used for multiple fixtures using a common drain.  We encounter these types of drains in public bathrooms or large kitchen.  All Fixtures drain into a vertical drain pipe which runs to a vertical stack to drain.  The venting will run from the vertical stack in the ceiling and tie into the top of the drain pipe at the furthest fixture from the vertical stack.  A Relief vent may be installed in the middle of the horizontal branch to help drainage.

In conclusion, understanding the intricacies of plumbing venting and the options available, like Air Admittance Valves (AAVs), is crucial for maintaining a functional and code-compliant plumbing system. While AAVs can offer a convenient solution in challenging situations, they come with limitations and potential code violations that every homeowner and plumber must consider. Proper venting ensures that your drains operate efficiently, preventing the harmful effects of negative pressure, such as siphoned traps and the entry of dangerous sewer gases into your home.

The best approach is always to consult with a licensed professional who can assess your specific situation and provide solutions that meet local plumbing codes. Remember, cutting corners might offer short-term relief, but ensuring your plumbing is correctly vented and up to code will protect your home and health in the long run.

Taking responsibility for the integrity of your home's plumbing system not only safeguards your investment but also ensures the safety and well-being of everyone under your roof. Trust in expert advice, adhere to local codes, and prioritize proper installation to avoid costly and dangerous mistakes down the road.

R.C. Szabo Plumbing & Sewer
Plumbers in Midlothian, IL 60445

Call us at: 708 601-2347
Visit our website: rcszaboplumbing.com

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